Transcript for:
Understanding Central Nervous System Functions

okay so in today's lecture we are going to continue our discussion of the central nervous system and this is part two of the cns chapter um [Music] we have talked about the two major organs of the central nervous system namely the brain and the spinal cord talked about the different brain regions what we need to discuss here in this lecture is kind of wrap that up but mostly focus on higher order functions of the brain where we will discuss the limbic system and then the reticular formation and then about memory we'll touch on language brain waves eegs things like that and then move on to our discussion of the spinal cord so let's kind of get started and talk about two major functional brain regions or brain systems or networks um the two networks of neurons i want to talk about here is the limbic system in the reticular formation when you think about the major cells within the brain or the spinal cord where you expect to see majority neurons and all of these other supporting cells like the neuroglial cells um astrocytes epidermal cells um schwann cells oligodendrocytes and so on and so forth the the star players though of the entire brain and the spinal cord the nervous system as a whole would be neurons okay but a neuron does not work by itself it doesn't work in isolation it's always you think about this as a network of neurons you think about it as hundreds thousands tens of thousands and sometimes millions of neurons all kind of working together within a particular functional system to get complex functions related to the brain accomplished and so what i want to describe is two such networks one network is called the limbic system which is really kind of related to um what we call the emotional brain okay if you remember the different regions of the brain uh you had different lobes there were five different lobes the the frontal the parietal the temporal the occipital and then the insula that was kind of hidden deep inside um the frontal well all all the major lobes have uh what we called association regions and there was one very specific region called the prefrontal cortex in the frontal lobe and this was really important for higher order functions like um like you know recognition you know reasoning logical thinking problem solving all of that that's what we call the cognitive brain because that's that's more the rational brain what i want to talk about is a slightly different aspect of the brain or in terms of brain functions now the limbic system is more your emotional counterpart okay and so i'll show you which regions make up the limbic system and then this is super important number two here which is the reticular formation which is part of something called the ras the reticular activation system so i'm going to start with the limbic brain first and then move on to reticular formation okay here's a side view a lateral view of the brain and if you can kind of orient yourself this should be the front of the brain and here's the back of the brain okay so you're kind of seeing the cerebellum is is not shown you should have been out here on the bottom you don't see the brain stem or the spinal cord or anything like that you're looking at all of this gray region this should be your cerebral cortex this is the gray matter that you see on the outside of this of the cerebrum the the brain all the white matter is kind of hidden on the inside so when you're looking at the cerebral cortex okay so the front part of this brain here this is uh if you remember this is the frontal lobe and then you had your parietal lobe and of course you're seeing one half one cerebral hemisphere so think about the other half on the other side which also has a parietal lobe here at the back you see the occipital lobe and then right there at the transverse i mean at the lateral fissure you're going to see um lateral celsius you're going to see the the temporal lobe the insula if you peel this apart you're going to see the insula the fifth lobe kind of hidden deeper inside so now that you've kind of oriented yourself with the different brain regions the prefrontal cortex is makes up like the majority of this region here that's the cogniti that's the cognitive brain that's the the rational brain okay the limbic system is shown in these structures here uh kind of almost all of these structures here in red all of this and then this is kind of hidden in the core of the brain like deeper inside that makes up the the emotional brain and it really consists of structures within the cerebrum okay and you see several listed here for you in red the cingulate gyrus that's a important one the amygdaloid body i'll explain to you what these two do here in just a little bit hippocampus super super important this is part of the emotional brain but the hippocampus also plays a huge role in memory okay in association with the with the lat um the temporal lobe um so those are some of your cerebral structures that make up the limbic brain so if you ever see these structures okay on your exam you see singular gyrus so you see the amygdaloid body the hippocampus you should know that this makes up the limbic system on the diencephalon side of things so if you remember the cerebral cortex then leads kind of into the diencephalon where you had the epithelius and the hypothalamus so the hypothalamus in itself is part of the limbic brain very important the hypothalamus does a lot of different things um this is uh very closely associated with this um with a very important um gland called the the pituitary gland and the hypothalamus controls pretty much all of the autonomic nervous system which is the involuntary control of say the cardiac muscle all of your smooth muscle controls all of your glands all of that plays a role in sleep wake cycles controlling hunger thirst hypothalamus does a whole lot of different things but it is also associated with emotions uh feeling of being happy versus fearful and any of that is all related to the hypothalamus hypothalamus does not work by itself it works along with all of these guys here the the amygdaloid body and the cingulate gyrus and so on and so forth the mammillary body um is also kind of it those are paired structures that you see in the human and you kind of see it towards the towards the bottom end of the hypothalamus this also plays a role in the limbic brain so what does the limbic brain do okay let's let's talk about that now that you know which structures make up the limbic brain let's talk about a few few of these structures okay uh the amygdaloid body and the singulai gyrus i want to explain these two so when you are um in a conversation with somebody or you are interacting with your friend or anybody right being able to recognize facial expressions especially those that cause anxiety those that um raise a red flag like anything that's related to danger or any of the fear response all of this is recognized by the amygdaloid body let me back up okay i want to show you where the immediate body and the cingulate gyrus is so the singular gyrus is here towards that the very far end and remember this is all very deeply located within the within the brain the core of the brain the amygdaloid body is this this structure right there now you're not going to need to identify any of it i just want to show it to you in perspective so the amygdaloid body is important for recognition of fearful expressions so what does a singular gyrus do well once you recognize those face those facial expressions then your ability to express those your own emotions we are gestural um measures like say okay say you were um in a confrontation with someone right so you can see that this person standing in front of you you're seeing that they're angry they are you know flailing around and all of that you know and so what what happens is the amygdala body is able to recognize those fearful expressions or those those facial those emotional responses and then what the singular gyrus in you is going to then respond to that dangerous situation uh certain things that you might do is probably frown or you may take a few steps backwards or you might want to exit the scene all of that would be the singular gyrus being able to kind of show those emotions or mostly facial expressions okay so the emotional brain has to work hand in hand with um the prefrontal cortex which is where you see the cognitive brain okay let me back up the prefrontal cortex is pretty much all of this region right here this is the cognitive brain it has to work um and communicate with all of these structures here which is part of the limbic brain okay so it's always a very tight relationship between how we feel and how we express our emotions which is related to the limbic brain and our actual thought process of being able to reason out what's going on in a particular situation which is a cognitive brain okay and a lot of this is kind of tied in together via the hypothalamus the example i want to give you here is um oftentimes i'm sure many of us have been through a situation like this is oftentimes you are in a situation where you know um again let's talk about that example of a confrontation with your friend for example and so so the emotional brain the metalloid body the singular gyrus all of this is responding and your limbic system is is processing all of these emotions that's going on and at the same time it's it's relaying all those emotions and all of that information to the prefrontal cortex where the cognitive brain is and your cognitive brain is probably deciding okay well you know what this is a this is a situation that's escalating it probably best to to not um you know react right now probably it would be best to maybe walk away till everybody calms down that's probably your cognitive brain uh that's responding to those emotional situations but at the same time you often see this your emotional brain can override your cognitive brain and um against your better judgment you may actually emotionally react to where you might actually you know i don't know get confrontational even more or escalate the situation which is against your better judgment that the cognitive brain is asking you to do so oftentimes you see you understand this is a communication between these two the limbic system and the prefrontal cortex and one's the the rational side of things kind of explaining okay what's right what's wrong what's the best situation right now that's a cognitive brain the emotional brain is just that it's your emotions taken over but it's a pretty interesting interplay between these two regions of the brain in terms of accomplishing of a higher brain function which is namely cognition okay and and being able to react to a particular situation so that's one aspect of um that's a fun that's one example of a functional system the second example of a network of neurons that i want to talk about here is the reticular formation okay so first where is this located and two what does it do okay so the reticular formation is really important for consciousness so i'm going to talk about um coma and things like that here in just a little bit so the reticular formation is what helps to filter different sensory inputs as it is received um through the spinal cord and sends it up to uh the different regions of the brain where you're processing all of that information so the ability of your brain to stay awake or aroused during the daytime is because the reticular formation is awake and activated okay so where exactly is this it is located as three broad regions or columns uh associated with the brain stem so let's look at this uh schematic right here to again you're looking at the mid-sagittal view of the brain here all of this is the cerebral cortex that's going to be the front this is the posterior end so you're seeing the occipital lobe here at the side here's the cerebellum here on the bottom all of this is the cortex region the gray matter region you see the corpus callosum which is your white matter tract right there on the inside and you're starting to see the ventricles all of that okay so what i want to point out is this um all of this region is going to be okay that's the thalamus region which is part of the diencephalon and you're seeing the pineal gland over there which is part of the epithalamus of the diencephalon and then all of this region here should be your hypothalamus super important region with the pituitary gland associated with the hypothalamus so all of this is the diencephalon region all of this particular region right then right after the diencephalon you should see the brain stem where you start to see the midbrain region and all of this is the pons and here's the medulla oblongata leading downwards into the spinal cord so that is it in essence the the organization of the brain and the spinal cord your two cns structures so where's the reticular formation all of this part shown here in purple um again like i said these are broad columns of basically these are called tracks tract tracks that helps to carry information to and from the brain so it is associated with the entire brain stem and if you if you recall brain stem consists of three regions okay you've got the the midbrain the pons and the medulla oblongata so all along the length of the brain stem you're gonna see this these columns kind of shown here in purple this is the reticular formation okay so what does it do well it's uh it's a very important highway if you will helping connect information from the spinal cord down here which obviously through its spinal nerves is able to tie in all the peripheral nervous system and carrying all of that information kind of shown here in blue all of this is sensory information that i'm carrying towards the center of the brain this is the thalamus region and then from here you're gonna radiate it you see all the purple arrows uh you're gonna take all of that sensory information to different regions of the of the cortex the cerebral cortex where you would make sense of it now depends on what type of information we're talking about this sensory information could be visceral information from anything related to from the skin for example related to touch or pain or temperature sensors pressure sensors things like that so all of that sensory information obviously uh blue arrows this is sensory inputs they need to go into the brain region specifically in the parietal lobe where you have your somatosensory cortex that makes sense of these perceptions of pain or touch or temperature or whatever right you also have sensory information from what else special senses as you can see here eyes so visual information is processed this is through the optic nerve and carry it down through the thalamus but then sensory information related to vision is processed way back here in the occipital lobe so that's where that information should be carried but what's happening here is your wrasse or your reticular formation is like your major highway that helps to direct all of this sensory information then you have your years that's going to have all of the auditory impulses being carried in and that's going to carry it to the temporal lobe where you process that information so your reticular formation helps to direct all of these sensory inputs to the different regions of the cerebral cortex where you're making sense of those inputs okay that's one thing the second thing as you can see here with that red arrow this is descending information this is a motor output out of the brain okay so if um if this is somatic output for example uh coming from the primary motor cortex in the in the frontal lobe all of that information telling the muscles to contract in a particular region of the body all of that has to be sent sen sent out through the thalamus through the reticular formation and out through the spinal cord where then spinal nerves will take that information to different skeletal muscles to bring about contraction and obviously movement related to that particular group of or that particular region okay so that in essence is the function of the reticular formation make sure you know where it is located it is it is tied in with the brain stem region and then here's some examples of what exactly it is capable of doing in terms of functions so again the ras the reticular formation in a source which is part of the reticular activating system is what's important to keep the cerebral cortex alert and in a state of consciousness okay so let me back up when you uh take a nap when you go to sleep in the nighttime grass shuts down basically it basically takes a break too it goes to sleep when it is not functioning then all of these sensory inputs and motor outputs are not passing through the rest this is why when you are asleep you are not processing sensory information you are not sending too many motor outputs to where you are moving moving around too much so i mean a few things that obviously is still passed through um you still have to control breathing movements and and things like that while you're asleep but in general your entire body kind of shuts down temporarily to a state of unconsciousness which of course you can be aroused from when you're awake right so remember the reticular formation is important for controlling the cerebral cortex and to keep uh the cortex in a state of consciousness or alertness okay this is pretty cool remember all those sensory inputs have to go through the ras so that it can be compartmentalized in different regions of the brain cortex um to make sense of it right whatever that sensory information is 99 of all your sensories tip inputs your stimuli do not pass uh they get filtered out by the wrath this prevents sensory overload so you can probably relate to this when you are going through your day you you encounter so many different people you do so many different things you pass by so many different people and so many different events and circumstances you don't remember all of that you don't process a lot of that um even if you were like if you were like in a classroom for example and you were kind of looking around you probably remember who was in your class or who was seated next to you but you may not remember exactly what they were wearing or were they what was their hair braided and and things like that i mean all of this sensory information that you are you are your eyes are receiving a lot of that sensory information your ears are hearing a lot of that auditory information but you don't remember it because you're not really processing every single detail of every little thing every stimulus that occurs throughout your day simply because the reticular formation and does a very fine job of filtering out all the noise all the background stimuli in your life okay only helping you process and remember and make sense of things that are relevant to your life and most important okay so that's something that's controlled by the rest of course like i said a while ago it can be inhibited when you're sleeping uh so sleep centers and of course it is inhibited if you consume too much alcohol and this is why you know you can kind of get drowsy you can kind of lose control over your cognitive functions of course drugs do that as well okay okay so if the ras and the reticular formation especially like the brainstem region the medulla oblongata if it uh sustains any excessive trauma it can really damage the brain stem region it can damage the wrath causing you to go into a coma which is permanent unconsciousness okay all right um other things that the ras is controlling because it is right there on the brainstem and the medulla oblongata has all of these different centers it does help with a respiratory sense helps to maintain your rate of breathing helps to increase your your depth of breathing so either slowing it down or increasing it depending on what kind of stimulus your body is receiving it also controls cardiovascular functions so cardiac center helping to regulate heart rate and how fast your um your ventricles are contracting how what's a force of contraction uh how much blood is being pumped out so therefore cardiac output so all of that's controlled by the cardiac center where on the medulla oblongata which is part of the reticular formation vasomotor centers this is related to um the vasculature the blood vessel so being able to control blood pressure okay so um when your blood pressure drops uh uh your blood vessels need to respond a particular way when your blood pressure increases it does right the opposite so let's start with what happens if you have elevated blood pressure then it brings about an opening of the lumen of the blood vessel this is vasodilation so vasodilation basically allows more blood to flow through less resistance therefore brings down your overall blood pressure right the opposite if you had low blood pressure then it brings about the laser motor center here um brings about vasoconstriction where it narrows down the lumen of the blood vessel making it harder for blood to flow through increasing the resistance and therefore increasing your overall systemic blood pressure so all of this is controlled by the vasomotor center on the medulla oblongata which is all part of the class okay so the ras helps to to maintain a sense of consciousness and being alert but also has all of these other autonomic centers related to involuntary control of the of the cardiovascular system the respiratory system okay um let's talk about language next this is another um complex function related to the cns uh the the brain specifically i wanna remind you of these two regions um that are typically seen in the brain normally on one cerebral hemisphere normally it's on the left side um there are two main regions the brokers area and the wernicke's area the brokers area actually i think i have a schematic right here okay um this is this is from part one of your slides your cns slides i just wanted to bring this in here so you remember where we're talking about so here's my central celsius which divides out the frontal lobe and the parietal lobe behind it so all of this purple region this is where you saw the association regions we just talked about the prefrontal cortex this is important for the limbic brain okay but i'm sorry prefrontal cortex this is important for the cognitive brain but right next to it you should see here by these uh dotted lines this region here this is the broker's area this is part of the frontal frontal lobe this is important for speech production so being able to control muscles that bring about your ability to produce sounds to produce words uh sentences and so on and so forth so production of sounds speech production is carried out by the brokers area right here then associated with this you have another region here towards the back this is all part of the association cortex this is mostly in the temporal lobe a little bit in the parietal lobe as well um you have another region here called the vernicke's area so all the speech that is produced by the brokers area now needs interpretation so making sense of those words and what exactly is the meaning of those sentences all of that is carried out by the wernicke's area so both these areas together work together let me back up to bring about language okay so make sure you know the importance of these two different regions now while i'm talking about language um we need to mention dominance cerebral dominance so you've got two hemispheres cerebral hemispheres you've got the left and the right in most people the left side the left cerebral hemisphere is considered more dominant um this is really where you're processing language you're processing math um more complex uh complex math things like that so that's your more um that's your more uh i guess your cognitive side of your brain if you will but but more in relation to carrying out complex functions uh like math processing and things like that and language the its counterpart on the right cerebral hemisphere uh controls language but a different kind of language this is more body language this is expressions this is more your emotional side this is um this is more related to the right hemis hemisphere would be more related to artistic side uh so not so much the math side okay so they kind of even though anatomically speaking you have the same regions the functionality of the left and the right cerebral hemispheres varies depending upon which right which region controls language and math versus which side controls more of your um your artistic side your body language and things like that whichever side controls language and math this is considered the more dominant side of your brain the dominant brain or the dominant hemisphere and in about 90 to 95 percent of individuals the dominant side the dominant hemisphere is the left side okay um typically if you are left left brain dominant you tend to be right-handed when writing and vice versa okay of course there are people that are ambidextrous there are people that have compartmentalization that's slightly different to where it is shared by both the left and the right brain but that's a minority of uh in terms of percentages okay okay so the next um higher order function of the brain that i want to talk about is memory okay so first what are the regions of the brain that are important for memory the hippocampus this remember this we talked about this in association with the limbic brain as well just a while ago uh so the hippocampus plays a huge role along with the temporal lobes in memory and storage of information and retention of information there's two different types of storage of information on memory short term versus long term uh so short term again as the word suggests that's just a temporary holding place for certain information so for depending on how frequently you use that information that information can fade from your short term memory depending again on how how often you connect with that information moving any information from short-term memory into long-term memory would result would basically involve something called memory consolidation as well and generally speaking the more you work with some information or the more you have need to um think about specific facts or pieces of information uh the more repetition you have related to that piece of information that's when you move that information from short-term to long-term memory okay um memory consolidation like i said is part of this process so this is where you are consolidating or you are integrating new pieces of information with previous memories or previously stored information if you can fit or if you can find an association between new information and previously stored old information or previous memories if you can find that link or that connection this is consolidation this is what helps you to retain that information in long-term memory okay um so just remember the two types of of memory and where which regions of the brain are important for this uh function so let's talk about one important homeostatic imbalance related to memory loss so if the hippocampus and or the temporal lobe gets damaged depending on the degree of damage you could have different degrees of memory loss okay so bilateral destruction of both the lobes both the temporal lobes on both sides can cause widespread amnesia so amnesia is memory loss there's two types of amnesia anterograde and retrograde so anterograde is basically all of your old memories everything uh from way back you remember all of that but you do not this is this is where the person lives in the here and the now meaning you cannot remember what happened earlier this morning because you're not able to consolidate that information with previously stored memories so you're not able to make that connection so it's almost like you have recollection of everything in the past or you go back 50 years 60 years seven years you can remember all of that but you cannot remember short-term events that happened uh the pre yesterday or this morning often happens with the elderly so this is anterograde amnesia retrograde amnesia this is right the opposite this is where you lose all your memories from the past it often happens when you're in um when you when you've experienced uh severe trauma to the brain like you were in an accident or something like that and you completely lose uh recollection and any association of who you are and who your family members are or related to the past so going forward you can form new memories and you can transfer them obviously into long-term memory but you do not remember anything from the past that would be retrograde amnesia so those are the two homeostatic imbalance situations related to memory loss okay also continuing um to talk about higher order brain functions let's talk about what's an eeg this is an electroencephalogram what are the four different types of brain waves that you see alpha beta theta and delta waves and i'm going to describe these for you and explain to you their frequencies and when you would see each of these different brainwave patterns once you know what's normal for a person like what to expect in terms of brain wave function you can use an eeg to diagnose brain lesions any tumors in the brain uh infections abscesses um um any kind of condition related to epilepsy things like that so let's describe what's normal the normal is four different types of brain waves alpha beta theta and delta which is kind of described over here and i'm going to use the next schematic to put this into perspective but this is a good word slide for you to to get some information out of it and remember in terms of frequency starting with the highest frequency waves these are alpha waves you don't specifically need to remember um kind of like the numbers um well actually the beta waves are even more high frequency but the alpha and beta are considered higher frequency then you go into more of your low frequency waves your your theta and your delta waves so your high frequency waves alpha and beta are typically when you are very alert okay um your delta waves this is when you're sleeping so these are lower frequency waves so i'll explain what that means to you you'll probably it'll make sense when i'm showing you these graphs here so your alpha waves let's have a beta beta these are your highest frequency waves meaning all of these little peaks are coming together very quickly that's why they are high frequency waves in any given period of time you have many peaks closer together so that's why it's a high frequency wave this is what you see beta waves is what if if we hook any of you up right now and myself included if we hook ourselves up to an eeg right now we should hopefully hopefully right hopefully be able to see these beta waves right now because hopefully we are awake and alert and processing all of this information that's being discussed in this lecture okay now as you start to kind of doze off which hopefully none of you are you would transition from the beta waves into the alpha wave so this is where you are um you're awake you're still processing information but you're in a more relaxed state of mind this is typically what you do like if you were reading a book right before you fall asleep and you're kind of dozing off and not enough that would be your alpha waves okay theta waves are normally or mostly seen in children not normally seen in adults so we kind of lose this particular kind of waves as we get older okay so you go from awake beta waves to slightly drowsy alpha waves to completely deep in sleep that would be your delta waves okay now notice your compare your beta to your delta beta waves a lot of these peaks coming very very very closer together that's why it's high frequency look at the delta waves much more spread apart that's why they are low frequency waves okay so you would need to know when you expect to see these waves uh these different types of brain waves um in an individual so beta is for alert completely completely awake alpha is more relaxed and delta is deep sleep theta not seen in adults mostly only in children okay so when you are transitioning from being awake to a to deep sleep okay you're actually transitioning between all of these waves not theta so going from beta alpha and theta and delta um and i'm going to explain that to you in just a little bit let's quickly talk about consciousness because this is related to being awake and being able to um perceive different stimuli and sensation that your body is receiving so remember for your for your body to be in a state of consciousness think back to a few more slides when we started this discussion the wrath the reactive the reticular activating system has to be alert has to be awake in order to bring about this state of consciousness okay um so during a state of consciousness obviously you're able to control voluntary movements you're able to perceive different stimuli you're making sense of it you're making um decisions related to judgment logic memory all of that okay when you lose consciousness this is really where um your ras gets impacted okay this can be different types of impairment okay so if it's a brief impairment brief loss of consciousness most of us have probably experienced this when you you faint this is syn copy okay this is brief meaning somebody can arouse you out of this state of unconsciousness back to a state of alertness now coma this is where you go into an extended period of where you lose consciousness this could be naturally caused coma or could be a medically induced coma in in a hospital setting so that would be basically loss of consciousness where um you're not really able to arouse the person unlike as in the case of syncope okay now if coma extends over a longer period of time to where you cannot reverse it irreversible coma would be where you flatline your eeg goes into a flat line no activity this is brain death okay so that's consciousness so going back to your your um your different waves the alpha the beta and the delta waves let's talk about two different types of um sleep patterns okay related to your sleep wake cycle so you go in there's two different types of uh sleep patterns you have your rem sleep this is your rapid eye movement and then you have your end rem sleep which is your non-rapid eye movement typically when you go from a state of alertness to uh deep sleep you actually transition between different stages of rem and end rem sleep so you've got uh rapid eye movement and then you have nram stages one two three and four and uh the next uh slide should put this into perspective you typically pass through your rem uh rem kind of sleep and then your first two stages of n rem uh typically within about 30 to 45 minutes of your your sleep cycle and then it takes you a little longer to go into the deepest stages of sleep your deepest sleep is during end rhyme stages three and four okay typically if you've reached stage four that is your deepest stage of sleep typically takes about an hour and a half to get to that mram stage when you first um fall asleep during the night you stay in this nram stages three and four the deepest sleep stages for a longer amount of time um during um during your with the first part of your of the night okay as you get into the early hours of the morning you arouse from that deep stage and you will see yourself kind of fluctuating going from enron three and four to end one and two and sometimes if you're dreaming and things like that again you have your rem sleep as well that kind of kicks in you'll see yourself transitioning as you go into the early hours of the morning um as it gets closer to the time when you have to arouse and wake up uh when that rast system is is probably needing to get aroused this is where you're gonna see like you know three four five o'clock in the morning or whatever this is where you will see where you're not in the deeper stages of sleep as much you are more in your in your engram stage one or two or more in your rem sleep okay um for your deepest or your most restful amount of sleep you want to be in the deepest end drum stages three and four okay so let's kind of look at these different patterns here awake now what type of brain waves would you expect to see here if you were completely awake and completely alert this should be better waves okay better brain waves and then as you transition into um that drowsy state you would replace your beta waves with some alpha waves this is that relaxed state this is kind of where you start to see a lot of those alpha waves in your rem sleep rapid eye movement again um most of your muscles are inhibited uh except of course you want the diaphragm to still do its job because that's going to regulate breathing movements and then of course your the eye movements this is why it's called rapid eye movement your ocular muscles are are active okay most of the dreaming occurs in your rem sleep okay this is kind of what happens a lot in the early hours of the morning where you're not so much in the deepest stages of sleep you are more in your rem sleep where you are dreaming a little bit more again this is all characterized by your alpha waves okay then you move from rem into endurance sleep and you've got your stages one two three and four so in stage one this is where you're seeing most of your alpha waves so your beta waves get replaced by the alpha wave so arousal is still quite possible at this point so ram or nram stage 1 you can easily be aroused then you move into this nram stage two and this is where you're seeing where you have a combination of some alpha waves and you're starting to see some delta waves as well and also what you see here these spindles what we call sleep spindles you have these quick bursts of very high amplitude waves so this is very characteristic of stage two okay getting more and more difficult to arouse you at this point because you're slipping off into a deeper sleep state okay then when you go into these two states right here and stages three and four this is your deepest um sleep states this is where you're gonna start to see all of your delta waves okay your vital signs will start to decline at this stage meaning you're going to start to slow down respiration slow down cut heart rate and and your your pulse and all of that is going to start to slow down because you are in a more relaxed deeper sleep okay here and then in ending nram stage four this is again mostly all delta waves at this point this is typically where night terrors and sleepwalking may occur okay so you are not quite uh aware of what's going on at this point you are actually in a very deep uh sleep state at this point okay so like i was explaining on the previous slide going from awake to ram and nram stages one and two and everything this could take about 30 to 45 minutes depending on depending on whether you have sleeping problems and of course if you are extremely exhausted and tired you obviously go from that awake state to that nrem stage four pretty quickly if you're very exhausted so it really kind of just depends on your um energy levels but typically in a person that gets a decent amount of sleep uh five to six hours or so you go from awake to that stage 1 and stage 2 in about 45 minutes then it takes another 45 minutes or so to really get into these stages three and four so it takes about 90 minutes on average to go from a wake to that deepest stage four and rem sleep okay and then you're gonna cycle out of your stages three and four into your lighter sleep stages constantly throughout the night and like i said as it gets closer to wake up time okay that's when you kind of float around in these stages and you do not hit the the deep um deep sleep stages which is stages three and four like i also said on the previous slide for the most restful amount of sleep um to get to actually get um to replenish your energy stores you want to be in these two stages three and four you want to be there for a longer amount of time um and you want less of all of this because that's not deep sleep okay okay so now that we've talked about the different stages of of sleep uh rapid eye movement and then all four stages of non-rapid eye movement and rem sleep um we've already discussed um sleep wake cycles being that's controlled really by a very specific region in the brain within the down satellite called the hypothalamus this helps to regulate your um the times of day when you're awake versus your ability to kind of get drowsy and kind of fall asleep during the night time or unless it's flipped for you depending on what type of schedules you work but whatever is your natural biological circadian rhythm this is all controlled by the hypothalamus normally it's on a 24 hour kind of a cycle i'm gonna go with what's normal or what's what's normally seen in most individuals which is you're awake during the daytime and uh and then you get drowsy towards the night time so that is really kind of controlled by the hypothalamus um in a specific region um and these are two different basal nuclei regions within which is like kind of gray matter pockets within the hypothalamus called the suprachiasmatic clock or the suprachiasmatic nuclei and the preoptic nuclei this is really important the suprachiasmatic region because that's really where what we associate with the natural circadian rhythm or the biological clock okay now remember the hypothalamus has to work alongside uh the reticular uh activation system the ras pathway they both have to kind of communicate with each other to be able to control the state of consciousness or alertness okay so when the hypothalamus kind of is kind of controlling like with the sleep inducing center is able to control that state of drowsiness it's going to shut down the wrath in stages to where you go from an alert state to a drowsy state to a completely restful deep sleep state right and likewise right the opposite needs to happen as you are getting back into a state of wakefulness so this is when the hypothalamus releases certain chemicals or wake up chemicals called orexins and this is what stimulates the the reticular formation the ras to get aroused to kind of get come back to life and then that's able to then um communicate with the thalamus and is able to send sensory information back up into the thalamus and then you go from being partially asleep to fully awake okay so all of this is controlled by the hypothalamus and the reticular activation system okay okay that kind of wraps up our discussion of the of sleep patterns and sleep cycles and what's controlling all of this so let's move on to talk about some protection that is seen in the brain the brain is a very delicate organ it is encased obviously in an outer bony structure which is obviously the skull composed of the cranial bones and all of the facial bones um but between the skull and the actual brain okay which is extremely delicate you want a lot of protection okay to of course reduce friction to act as a cushion uh to afford more uh protection against trauma things like that there are three important brain meninges or membranes that helps to protect uh this delicate organ and we're going to talk about three layers uh the pier the pier matter the arachnoid and then the dura matter okay there are compartments there i'm sorry there are spaces in between these layers and i have a subsequent slide coming up where i'll show you all of these spaces some you're going to need to know the organization of the meninges and the different spaces in one particular space called the subarachnoid space you're going to see cerebrospinal fluid now thinking back to um our discussion of the brain um and a little later on when we move into the spinal cord as well there are fluid-filled regions or fluid-filled cavities within the brain are called ventricles there are four such regions two lateral ventricles one on each cerebral hemisphere so there's two lateral ventricles that are then connected together by the interventricular foramen and that connects with the third ventricle that you typically see in the diencephalon region and then the third communicates with the fourth ventricle sorry uh through the cerebral aqueduct the fourth continues downwards uh as the central canal which kind of goes through the spinal cord all of these brain regions these ventricles are filled with csf cerebrospinal fluid so this is kind of like gonna have it's gonna offer some kind of cushion but it's on the inside of the brain and flowing through it's a channel that flows right through the center of the spinal cord likewise the cerebral spine fluid is also seen wrapping around the exterior of the brain and the exterior of the spinal cord in a specific space called the subarachnoid space and i'm going to show you a schematic to put all of this into perspective but for right now um just kind of remember csf and this is really important the bbb blood brain barrier and i'll explain the importance of it what uh which features make up the blood burn barrier and how to prevent unnecessary toxicity in the brain okay let's start with the meninges three important layers uh there's several different word slides coming up i just want to put all of this into perspective using a schematic so hopefully i'll get to that slide here pretty soon here's the three layers uh the outermost layer is called the dura mater extremely tough uh the thickest layer right underneath it you're gonna see the arachnoid matter which is has more of a spider web kind of uh a kind of a structure where a lot of stringy kind of structures and i explained that to you and then the innermost layer right on top of the cerebral cortex clinging to it is a very very thin delicate membrane called the pier matter okay whenever you see inflammation in any of these three meninges this is meningitis okay uh csf is seen in a specific region between the pia and the arachnoid in a space called the subarachnoid space so that's where you typically see csf you're going to see blood vessels obviously which is going to supply nutrients to the entire internal regions of the brain and the spinal cord um helps to produce and helps to deliver glucose and amino acids and other ions that are important also helps to get rid of any excess waste which is typically what the vascular system does this schematic should put all of those three layers into perspective so here all this you this darker region has to be the outer cerebral cortex you're looking at the left and the right cerebral hemispheres for example uh the inner part the lighter part that's the white matter right so that's the brain this is all of the brain so right on top of the brain this extremely thin layer you can see this right here this is the pia the pure matter okay then i have this layer right on top of it which has all of these cobweb kind of stringy structures right there all of that that's the arachnoid matter okay and then on top of the arachnoid matter is where you see the dura mater which really has several layers to it i'm just going to call it the dura mater right now but that's the most robust the thickest layer uh right outside of the right on like the outermost layer of the brain and the dura is seen right underneath you all should recognize that that is basically the cranial bone if you're looking at a cross section of the of the skull cranial bone if you remember is kind of uh like a sandwich model i described this in the previous unit you got compact bone on on both ends and you see that you see the trabeculae the spongy bone here on the inside so all of that is obviously the bone and here's the connective tissue layers of the uh the periosteum that surrounds the bone so this kind of put this into perspective so that's the skull that's the bone right there here's the brain right so how do you protect the brain from that really hard skull well you've got three meninges in between which acts as protection okay so i'm gonna i've drawn it out here for you so the brain the cerebral cortex is all of this my squiggly lines right there so that's my cerebral cortex what's sitting right on top of the cerebral cortex that first layer is the pier pia mata what's the second layer the arachnoid and what's the outermost third layer the most robust layer dura okay and there are spaces between each of these layers okay so on top of the dura mater uh you see the epidural space epi meaning about talk right so about the dura mater that's the epidural space so then obviously the subural space should be below below the dura mater right obviously then you would see the subdural space in between the dura and the arachnoid matter okay and then between the arachnoid and the pier you have this last space here this is the sub arachnoid space meaning below the arachnoid matter right where do you see csf in this space right here the subarachnoid space that's where you see csf okay now keep this in mind i will i will bring this up in a later slide so this is the the arrangement of the three manages and the spaces in relation to the cerebral cortex okay all right here's an explanation showing you what these three layers are responsible for again dura most robust thickest layer mostly for protection arachnoid has these like i said these these extensions these um these stringy kind of structures the spiral web-like structures um most important thing about the arachnoid matter is that okay right underneath it where in the sub arachnoid space you have your csf you have all of your largest blood vessels all related to the subarachnoid space we will talk about the arachnoid valina in a subsequent slide so bear with me pia this is the innermost most delicate um connective tissue membrane that is sitting right on top of this river cortex tightly clinging to the outer structure of the cerebral cortex make sure you all know these three meninges okay when we talk about the spinal cord which is the other organ of the cs um the cns cerebral i mean sorry the central nervous system you're going to see the same three layers surrounding the spinal cord in the same order the the pia the arachnoid and the dura on the outside okay so it's the same three layers that protect both the brain and the spinal cord okay what do you see in the subarachnoid space uh you see csf you also see csf like i said uh within these ventricles these fluid-filled cavities within the brain and then that extends downwards into the central canal which is the fluid-filled cavity or the channel flowing right through the spinal cord okay so what's the importance of the csf um buoyancy uh this is what's going to allow the brain to to appear lighter okay if you did not have any csf inside of the brain then the weight of the brain as it rests on the base of the skull um especially on the occipital bone like towards the base of the skull where you see the foramen magnum and everything that the weight of the brain resting on the skull would cause damage to those uh to the posterior end i mean to those lower regions of the brain especially the occipital lobe so therefore that's a problem and to get rid of it or to reduce that uh you've got fluid filled cavities within the brain which allows you to reduce the weight of the brain by about 97 which really dramatically helps to protect the brain okay cushioning obviously any fluid filled um compartment offers friction resistance is able to absorb shock um so shock absorbance acts as a as a cushion okay and of course csf uh carries a lot of nutrients as well so it helps to nourish it nourish the brain okay the csf is formed from those blood vessels those blood capillaries leading into the brain and spinal cord um all that blood contains the the watery compartment of blood is called plasma so derived from that plasma that's how you get your csf okay the cool thing about csf is that you're going to see a constant turnaround of csf it has to be constantly recirculated between all the ventricles uh the central canal and then of course in the subarachnoid space which is what you see here so let me put this into perspective uh looking at the lateral view of the brain up there okay so you all should be able to recognize that occipital lobe here at the back parietal there uh frontal here up front um then here's all of your diencephalon region well this part right here all of this the thalamus the epithalamus and here's your hypothalamus over here associated with the pituitary like i mentioned a while ago and here's all of the brain stem region so the midbrain sorry the midbrain the pons and here's your medulla oblongata that's the cerebellum over there medulla oblongata continuing downwards all of this as the spinal cord right okay first things first um the brain is housed obviously in the skull which you should see that's the bony structure surrounding the the brain and of course the spinal cord is surrounded by the vertebral column and all of the vertebrae the cervical the thoracic the lumbar and all of that um so let's talk about where you see csf inside of the brain and then we'll talk about the spinal cord next so inside the brain you're going to see csf in the two lateral ventricles and since you're seeing the lateral view of the brain you're only seeing one hemisphere uh well this is actually kind of well not mid-sagittal but from this kind of like from the side um you're seeing only one hemisphere right here so the other hemisphere has been peeled off if you will it's right down the longitudinal fissure so that's going to be one lateral ventricle on one lateral um sorry on one cerebral hemisphere and then um right beneath it you see the third ventricle which is part of the thalamus region connecting that lateral ventricle to the third ventricle this opening right here this is my inter interventricular foramen and then all of that csf gets circulated from up there to the third ventricle and what does that these specialized neuroglial cells if you think back to your fundamentals of the nervous system where we talked about uh a specialized neuroglial cell called epinemal cells where they have these hair-like structures called cilia and what it does it helps to move the fluid across the surface of these cells and helps to move the fluid or recirculate the fluid between all of these ventricles so any fluid-filled cavity in the brain is going to see you're going to see these um epidermal cells lining these cavities so once you get into the third ventricle then it's going to flow through this narrow channel right there in the midbrain called the cerebral aqueduct and from there that csf is going to make its way into this last ventricle here which is your fourth ventricle and notice the location of it it is kind of right there in between the cerebellum in front of the cerebellum and kind of associated with the pawns of the brain stem region so it's right there in between those two regions all the csf is going to flow continuously because you've got passageways that are connecting all of this so this is all of the csf inside of the brain now i also want to continue downwards here the fourth ventricular will continue downwards as the central canal that opening right through the center of the spinal cord that's also where you see csf which allows csf to flow through the spinal cord okay so that's inside the brain and inside the spinal cord but right here at the fourth ventricle there are two openings a lateral and a median aperture and you don't really need to know the the names of it but there are openings right there that allows the csf to flow from that fourth ventricle to the space here on the outside now okay the the pure matter should be basically right on top of this cerebral cortex so you obviously don't kind of see it it's is it labeled it's probably not labeled okay so it's it's right here clinging to the cerebral cortex so the arachnoid matter should be your middle layer and that's what you see here in in this this purple this purple layer right there okay so the fluid from the fourth ventricle will exit through those two openings and then enter into this space here this blue space as you can see here this blue space is the space between the pier and the arachnoid matter let me back up where are we what's the space between the pier and the arachnoid matter called sub arachnoid space right okay so let me show you here so that's where you see all of that csf flowing all around the brain in the subarachnoid space and likewise all around uh this the spinal cord as well also in the subarachnoid space okay then uh like i was saying uh csf is is um formed continuously within the brain and the spinal cord and it is formed from these structures here these are a collection of blood vessels blood capillaries called the chloride plexus so the plasma within the chloride plexus is responsible for generating new csf well if you keep making new csf but there was no way to get rid of the old csf to reclaim it back into the the overall circulatory system then fluid is going to start building up here in the inside of the brain inside the spinal cord and in the subarachnoid space which is obviously a problem causes the the pressure inside the brain to increase which is not good so there's going to be a constant circulation of this csf as you're forming new newer csf so it's going to circulate through all of these passages enters the subarachnoid space where then drains out through these arachnoid villi so this this region here uh where you see that will be the dura mater so it then gets absorbed into these sinuses up here and there's different sinuses but basically they are their venous drainage okay and then from here all of this excess fluid excess csf gets absorbed back into the venous circulation where it becomes part of the plasma okay so as new csf is formed you got to get the older csf out of there so that you have a constant turnaround of the of the csf okay so i think i've covered most of these um structures associated with the um with the csf formation i already talked to you all about the epidemic cells this is going to help kind of circulate the csf and helps to cleanse the csf by removing removing vase as well notice every eight hours you would replace your entire volume of csf okay and that's why you want to constantly keep the csf in constant motion and the reason how how is that accomplished through the epidermal cells and all those how they're all connected together and then they get drained out through the arachnoid villi to the normal venous drainage okay so i think i talked about the chloride plexus that's how you generate the csf i talked about the importance of the epidermal cells all these are important concepts okay okay so i talked to you a while ago about you cannot have stagnation or um accumulation of csf inside of the brain because that's going to cause elevated pressure inside the brain this often times happens this condition is called hydrocephalus this happens because there's an obstruction preventing csf to circulate freely and preventing drainage let me back up to this to this schematic right here so normally the blockage is right here that's not always the case but most often this is this is where you see uh that blockage in that narrow channel there called the cerebral aqueduct so what happens is new fluid new csf is being formed here in the upper ventricles and it's not able to get past that obstruction right there which means it's not going to get to the fourth ventricle which means it cannot entire enter the arachnoid space subarachnoid space and therefore cannot get drained out so then you're going to see a backup of fluid in this inner innermost core within the brain resulting in hydrocephalus this is obviously a condition that is not desirable it can cause severe brain brain damage uh in in children well in newborns actually in babies uh actually this is countered better because um if you think about the the cranial bones they're not completely fused at that point the sutures have not they've not completely ossified this allows for as the brain grows it allows for um uh what you call it a little expansion of those uh plates of bone uh in the in the cranium which allows you to accommodate for some hydrocephalus but in an adult brain this is problematic because you have a very rigid skull where all the bones have been um kind of joined together those joints are if you remember called um sutures so they completely ossified um therefore um the only way to get rid of that excess buildup buildup of csf would be to drain it using a shunt okay okay and the last protective measure related to the brain is the blood-brain barrier okay you want to maintain very very carefully uh the internal environment within the brain you want very few chemicals to get through you want very few things to get through to to actually um get past the blood capillaries and enter into the the neuronal cells so the blood brain barrier is a very tight barrier consisting of tight junctions kind of have to think back to i believe chapter 3 when we talked about the overall structure of the cell we discussed three different cell junctions open gap junctions don't want those guys here gap junctions allows for too many things to pass through freely which is a problem we don't want gap junctions uh we talked about desmosome junctions in chapter three as well those were like yours like your rivet junctions that's great for regions where there's more mechanical stress and and friction not so much a problem within the brain so we don't we don't really need the desmosome junctions either what you need are those tight junctions tight junctions don't allow hardly any molecules to pass through this is the barrier consisting of tight junctions between your blood capillaries and if you remember capillaries are the smallest blood vessels they only have a single layer to their entire wall surrounding the lumen that allows blood to flow through that wall consists of a single layer of um i think back to lab where we talked about simple squamous epithelium which is a single layer of flattened cells kind of all become very squished together right so you have those simple squamous epithelial cells they are called specialized specifically in a blood vessel they're called endothelium so between those endothelial cells you want tight junctions this will prevent too many things from getting passed from the lumen of the blood vessel from the lumen of the blood capillary getting past it into the brain regions where you expect to see obviously neuronal cells okay so this type barrier is uh is super important it consists of your tight junctions between your endothelial cells which is part of the blood capillary walls and then surrounding that there's a much it's a thickened connective tissue membrane called the basal membrane or the basal lamina which allows for a second layer of protection and the third layer are these very important neuroglial cells called the astrocytes these astrocytes have these um foot like processes that are extended and kind of wraps around the capillaries and what it does is it basically allows for more formation of tight junctions so the three together make up the blood-brain barrier and is important because this is going to prevent too many things from passing through from the from the blood capillaries into the brain now of course certain things do pass through uh so it is a very selective barrier nutrients like glucose and amino acids have to pass through because you want those nutrients to form atp which is obviously important for the functioning of the brain okay you want certain ions to pass through of course water to a certain extent but very very few things actually get get past the blood-brain barrier okay so make sure you know the features of the blood-brain barrier what are some of the things that actually pass through like i said nutrients glucose and amino acids um most other things like waste products uh from the blood is not going to leave okay so larger proteins toxins any kind of microbes uh most of your drugs there are some exceptions um most of these basically do not pass through essential amino acids pass through but not the non-essential varieties so the ones that are mostly important for gluc atp production do pass through though the most important substrate for atp within the brain is really glucose okay um most of your fat soluble uh substances can pass uh here are some examples you know alcohol can pass okay through the blood brain barrier and can directly affect uh your cognitive abilities within the brain nicotine is another one that can pass through and of course in aesthetics some drugs can pass through as well okay this is very important it is a selective barrier but notice it says it is not absolute meaning it is this selective blood-brain barrier is not seen covering or protecting every region of the brain there are some regions of the brain where you will not see a blood-brain barrier it is absent what are some regions um like let me back up probably use use this as uh to put it into perspective the pituitary gland that's the pituitary gland there's two two lobes to it you have an anterior pituitary and a posterior pituitary you do not have a blood-brain barrier in the region associated with the posterior pituitary because there are two important hormones that need to be released from the posterior pituitary you may have heard of oxytocin which is important for labor contractions during delivery but also important for the whole lactation process being able to produce milk from the mammary glands after the pregnancy in a nursing mom um so that's one oxytocin the other important hormone that's produced by that posterior pituitary is vasopressin or vasopressin also called adh antidiuretic hormone this controls fluid levels water levels uh and of course then kind of also controls electrolyte balance in the body those two hormones are released from this region the posterior pituitary and there is no blood brain barrier in that region because those two hormones need to enter into the blood vessels so that it can be distributed systemically to every region of your body of course the oxytocin goes specifically to the uterus in the case of labor contractions or to the mammary glands for lactation but adh you're going to especially see that going into the like the kidney the kidney tibial cells and so on and so forth so you need you don't want a blood-brain barrier there you actually want those hormones to leave um the pituitary so that it can enter the bloodstream also associated with that region the hypothalamus specific regions of hypothalamus do not have a blood-brain barrier because a lot of these hormones are actually released from the adh and the oxytocin is released from the hypothalamus so kind of acts as a temporary holding place for those for those hormones so that's another reason or another region where you will not see the blood-brain barrier then right here the pineal gland that's another region where the blood-brain barrier is absent because the pineal gland releases another hormone uh melatonin which helps to regulate sleep-wake cycles so that needs to also gain access to the blood vessels so therefore no blood-brain barrier there and then specifically here especially here the medulla oblongata um this is one region that's not protected by the blood-brain barrier because it's important for many different functions like uh there's a respiratory center and a cardiovascular center all of that's fine but here's what's what needs to happen there's a there's a vomiting center that's associated with the medulla oblongata and this region needs to be able to screen toxins in the in the blood and that's why you don't have that blood-brain barrier there because when it detects these toxins then if it's something poisonous obviously it has to alert the body it has to alert the digestive system and it should basically bring about the whole the vomiting uh reflex so if for that reason the medulla is not protected um at least specific regions of the medulla are not protected by the blood brain barrier so the blood-brain barrier is seen in almost all the regions protecting the brain but there are specific regions where it's absent okay okay i think i've covered most of this uh let's talk about some homeostatic imbalances related to the brain um i'm going to go over this uh fairly quickly a lot of this is just a very very brief overview of some of the imbalances that we're going to talk about tbi okay so many many people have um loved ones that may have gone through tbi especially if you have military family members or military friends um many this is something that's talked about quite frequently tbi traumatic brain injury um so what's a concussion this is basically a temporary uh loss of function or altered function within the brain region if it's more permanent damage it's called a contusion a lot of tbi can be brought about because of hemorrhaging hemorrhage could occur in the subdural or the subarachnoid spaces so if you remember the subdural space is between the dura and the arachnoid and then the subarachnoid space is between the arachnoid and the pia so if there is hemorrhaging and buildup of fluid obviously in those regions this is obviously going to cause an elevated pressure in the brain this is all associated with tbi but more importantly this is what could result it could force regions of the brain stem especially the medulla to it can it can force it out of the skull and remember the base of the skull has this rather large opening in the occipital bone called the foramen magnum uh they can it can force the brainstem through the foramen magnum and cause damage uh to the brainstem now if you also remember earlier on in this discussion in this lecture we talked about the the ras remember that the reticular activating system where is that located on the brain stem associated with the midbrain the pons and the medullary so what happens if you force the brain stem downwards that's going to crush that region and it's going to damage that region and it damages the wrasse and what's the rest important for consciousness and alertness and that can obviously put you in a coma and of course that can severe damage can obviously put can result in ultimately death okay so this is all related to tbi edema of course is just basically swelling a lot of this could be related to um abnormal circulation of the csf uh causing cerebral edema okay but can also be related to tbi cvas cerebrovascular accidents also commonly called a stroke okay what this means is you most often this is because of an obstructed cerebral blood vessel and therefore certain regions of the brain get deprived of blood what's what's being carried in the blood nutrients like like um glucose and amino acids and oxygen so when you deprive the brain region of that of that blood supply uh because of a blockage in a cerebral artery this can cause what we call ischemia tissue ischemia which is where you don't get enough blood supply to that specific region okay now this can cause obviously death of neurons in that specific region depending on how long the ischemia lasts and how large the blockage is and obviously can cause ultimately a cva or a stroke okay now a stroke would result depending on which region of the brain gets impacted this can cause a loss of sensory function it can cause a loss of motor function just depending on which brain region was impacted so if it was the primary motor cortex within the frontal lobe then that's going to impact a lot of your motor function if it is within the parietal lobe and then that's going to cause a loss of sensory function so if you see paralysis on one side which is um this is hemi hemiplegia um this could be um so that's hemiplegia and then of course you can also see uh not a full-blown cva or a full-blown stroke but something that is more transient and this is uh what we call a tia a transient ischemic attack and lasts from five minutes to 50 minutes uh impairing the oxygen and the nutrient delivery uh to different regions of the brain um if you if your doctor does the right kind of diagnostic test and figures out that there is an obstructed blood vessel within the cerebrum of obstructed cerebral blood vessel um the best approach especially if if you are at risk of a stroke and your your tissue is experiencing a lot of ischemia or deprivation of blood supply the the the only clinical intervention uh to quickly bust open that clot or to to break up that clot that obstruction in the blood vessel this would be using tpa tissue plasminogen activator this is the only treatment that has been approved for stroke the next homeostatic imbalance of the brain that i want to talk about is alzheimer's disease this is an irreversible progressive brain disorder that typically slowly destroys memory ability to to think through uh different situations and of course even to be able to carry out the most simplest tasks ultimately um so a lot of people with this degenerative disorder um ultimately have memory problems they have a short attention span they tend to be very disoriented um language loss irritability moody very confused and ultimately hallucinations as well alzheimer's is currently ranked as the sixth leading cause of death in the united states it is the most common cause of dementia among older adults dementia is basically where you have a loss of cognitive functioning you're not able to to reason things you thinking remembering reasoning all of those are affected and of course you also have behavioral issues as a result resulting from this uh lack of cognition so like being moody and irritable and so on and so forth um typically people that have alzheimer's this is kind of some of the features clinical features that we notice in the brains of people that have had alzheimer's as you typically see these abnormal clumps which we called plaques and they're made up of a certain protein called beta amyloid so they're they're beta amyloid plaques or clumps that typically form in specific brain regions and they have very toxic effects along with these plaques you're also going to see um tangled bundles of fibers which we now call neurofibrillary tangles or tau tangles and what happens is this ultimately affects the neurons in those regions uh causing degeneration and destruction of those neurons as a result you lose functionality associated with those specific neurons and with those specific brain regions as well causing brain to shrink um specifically in the regions of the hippocampus uh the forebrain and the cognitive regions of the cerebral cortex let's say for example the prefrontal cortex if it's related to memory loss then it could be regions of the temporal lobe um so if you if any of these regions are impacted by degeneration of neurons because of these plaques and these tangles that are formed inside of the brain that could result in all of these different clinical characteristics that are associated with alzheimer's disease like um loss of memory and of course um be not language loss and irritability and other other uh emotional kind of emotional and cognitive kind of disability in parkinson's this is associated with degeneration of a specific most more than likely it is associated with one specific region called a substantia this is a specific brain nuclei region within the midbrain region of the brain stem when you have a loss of dopamine producing neurons this can cause uh these neurons to become overactive causing a lot of tremors or shaking that is often characteristic of parkinson's disease there are so many other things that we're trying to learn about parkinson's disease and now there's uh indication that this might be related to mitochondrial dna abnormalities uh so it could actually be a mitochondrial disorder and there's a lot that needs to be studied related to this but in general it what we do know is one of the predominant causes of this disease is loss of neurons within this specific region the substantia okay can be treated with uh several well el dopa that's that's really the most important um treatment strategy for parkinson's of course there's other gene therapy um approaches that are being explored right now stem cell transplants and then so on and so forth as well okay i think that wraps up the brain i'm going to get started with the spinal cord which is the other important uh organ within the central nervous system i want to just quickly explain the orientation of the spinal cord and the spinal nerves um to kind of get us started with this discussion on the spinal cord okay so if you remember the brain the brain the the the distal part the most um the last part of the brain is basically your brain stem region where you have your mid brain the pons and the medulla oblongata the medulla continues downwards as the spinal cord the spinal cord is protected in that bony vertebral column now if you remember the thinking back to your skeletal um system and whatever you've learned in lab related to the vertebrae the classification you had several different regions the cervical vertebrae and then you had the thoracic vertebrae and then the lumbar and then you had a like a fused sacrum region and then the tip of it which is the the coccyx um now the spinal cord is housed inside of all of those vertebrae inside the vertebral column but it doesn't go all the way down to the sacrum and the coccyx it actually ends so it's through the cervical through this thoracic region but it actually ends on the top part of the lumbar vertebrae typically l one lumbar vertebra one maybe l2 l1 l2 that's where the spinal cord ends okay now um what's the main functions of the spinal cord well it is like your major highway connecting all of the peripheral organs like your upper limbs your lower limbs the abdominal region everything all of that is connected through spinal nerves from all of these peripheral organs ultimately into the spinal cord and then all that information is carried uh through the spinal cord into the brain stem and then to the specific regions of the brain so your spinal cord is like uh your your connection if you will between everything peripheral sorry peripherally located to towards your brain okay so it's kind of your connection the other important thing about the spinal cord is major reflex center um so we will talk about different reflexes in the in the pns chapter a little later on uh so we we will discuss like the stretch reflex and things like that later on but a lot of your reflexes are entirely controlled by the spinal cord with no communication or very little control from the higher brain regions okay so coming back to the anatomy i said the spinal cord ends at at the level of the l1 or the l2 vertebra in terms of protection just like the brain like we talked about a while ago it has the same three meninges you have the immediately surrounding the spinal cord you've got the pia and then you have the arachnoid the middle layer and then the atmosphere is the dura okay now the cool thing about the spinal cord is outside of the dura in the epidural space okay you also have a lot of adipose tissue there that acts as additional cushioning and a protective measure to to absorb um blows and like basically trauma okay that's kind of what's shown here the epidural space and i'll show it to you in a schematic as well and i'll talk to you about the lumbar puncture in this next slide i need to show you where exactly that would happen so here's the the the cerebellum that's the brain stem region like the base of the um the brain um and then the rest of this is going to be all of this is going to be the spinal cord that extends right down through and all of these and you can kind of see the cross section of the different vertebrae right there so you've got the cervical vertebrae the thoracic the lumbar and here's the sacrum right there with the tip of it being the coccyx so notice the spinal cord doesn't go all the way through it actually ends right there it forms a cone-shaped tip which is called the conus medullaris at the level of your lumbar one or your lumbar two vertebra okay that's where the conus medullaris ends now what i want you to recognize is at each level of the vertebra like cervical vertebra one cervical vertebra two three four five six seven and then you have your thoracic one two three four all the way to twelve um at every level of the vertebra exiting from the spinal cord you have a pair of spinal nerves so they're matched on both sides so you have a pair of spinal nerves at the level of cervical vertebra one you have a next pair of spinal nerves at the level of c2 and c3 and so on and so forth so we end up with so each of those those yellow structures that you're seeing on either side fasten kind of um in between the vertebrae those are your spinal nerves and there's 31 pairs of spinal nerves okay let's talk a little bit more about this um the tip of the spinal cord like i said was the conus medullaris okay pass this l1 or this l2 region so what happens to spinal nerves l3 l4 l5 and and so on and so forth well all of those will not because remember the spinal cord has ended so so it's all going to freely hang loose like that on the bottom as a collection of spinal nerves and this collection is what we call the corda equina the horse's tail okay and then you're going to see but at the at the level that they need to exit out you're going to see them emerge out at that level of the vertebra okay a few more things i want to talk about remember the layers that protect the spinal cord the inner most layer is called the pia the pier is going to wrap around the spinal cord remember the spinal cord ends right there at l1 or l2 but the pier continues it continues downwards and it attaches right there kind of kind of in there closer to the the sacrum and the coccyx region this is called the phylum terminal i think that's kind of shown here in in the green okay so all the way down there to the coccyx the phylum terminal is where the pier attaches all the way down to the coccyx and so what it helps to do in this case is it prevents the spinal cord from flopping around so it gives it more security to where it is attached firmly to the sacrum region now coming to that lumbar tab what about the other two layers the arachnoid and the and the dura they will continue a little further down probably to the top of the sacrum now the subarachnoid space if you remember this is between the pia and the arachnoid matter and that's what's filled with fluid csf so if you wanted if there was an infection and you wanted to take a sampling of the csf of that fluid you don't want to touch any region where you still have a spinal cord intact because it can cause unnecessary damage if it slips and if you don't do it right but instead after the spinal cord is ended so like safe to say l2 so between the rest the rest of the region so l3 l4 l5 the lower lumbar region that's where you don't have a spinal cord but you still have the subarachnoid space with the sampling of the the csf fluid so you can insert a needle and draw a sample of the csf from those regions and this is why this is called a lumbar puncture or a lumbar tap this occurs in the lower lumbar regions where you still have csf but there's no spinal cord damage that the reason for this is again is if you wanted to screen the csf for any toxins um infection inflammation things like that so that you can come up with the right treatment modality to uh to treat that condition so now that we've talked about spinal nerves what i want to do next is discuss uh the overall gross anatomy of the spinal cord itself showing you where you would expect to see the gray matter versus the white matter where do you expect to see the csf and all of this in relation to how the spinal cord kind of fits within the the vertebral column and i want you to pay attention to the anterior aspect of the spinal cord which is also ventral or the and the posterior aspect the dorsal aspect of the spinal cord so what you can kind of see here is uh one of your vertebrae okay and if you have to think back to what you've discussed with the skeletal system and the features of a vertebrae so you're looking at the body of the vertebrae here up front from the anterior aspect and here's a spinous process related to what you would see on the posterior aspect of that vertebra the transverse processes and the intervertebral foramen is kind of what you're seeing here on the left and the right um so when you're looking at this particular vertebra this cross section of this vertebra on the inside here this is the cross-section of the spinal cord at that level of the vertebra so obviously this is going to the entire spinal cord is going to be situated here in the middle in this opening here which is called the vertebral foramen that's a feature that we covered in lab so when you're looking at the cross-section of the spinal cord i want you to recognize that the grain the white matter orientation is switched um relative to what you expect to see in the brain within the within the cerebrum so in the brain you had gray matter on the outside called the cerebral cortex and on the inside you saw the white matter tracks it is right the opposite in the spinal cord where you see the gray matter this darker region here that's seen on the inside of the interior of the spinal cord and on the outside here you're actually seeing the white matter okay on the very center of the spinal cord there is a channel this channel is uh the central canal and this is where you're gonna see um cerebral spinal fluid um so make sure you can identify the different regions of the spinal cord and i want to kind of point out this is typically how i remember this is if you're looking at the overall shape of the the gray matter kind of looks kind of resembles kind of like a butterfly uh with the with the wings on on the top there so the wings kind of point towards the posterior or the dorsal aspect of the spinal cord and the rest of it is what you should automatically uh refer to as the anterior aspect so look for the look for the elevated regions right there like you like the butterfly wings and that would be the posterior aspect and this is going to be important because we're going to define three different regions within the gray matter um this this portion here on the top is called the dorsal gray horn which means this the opposite region of the of the gray gray matter will be your ventral gray horn so dorsal will be the top of those butterfly wings because it's facing towards the back towards the posterior aspects of the dorsal greyhound and here's the air the ventral greyhound which raises towards the ventral or the anterior aspect of the spinal cord which then leaves us with this little portion here uh that should obviously be the lateral greyhound so dorsal lateral and ventral gray horn likewise the white matter and i'm going to show it to you in a on a slightly different schematic is also organized to match the gray matter you've got the the dorsal the lateral and the ventral funiculus um in terms of protection for the spinal cord um surrounding the the spinal cord you've got the same three layers the same three meninges except these are spinal meninges as opposed to cerebral uh meninges um you still have your innermost layer and this is um if you can kind of follow with me this innermost layer the thinnest layer that sits is in direct contact with um with the spinal cord is the pier matter and then this white layer that you can kind of see there that's basically your arachnoid matter where you have all of those spider web looking projections as you can see um we're very similar to what you expect to see in the brain like we discussed in a previous slide and this outer layer right there that's going to be the dura mater okay if you remember the the spaces that we talked about between the pier and the and the arachnoid so right there between the pier and the arachnoid you expect to see the subarachnoid space and this just like the like the brain that we discussed a while ago is where you also see csf so csf is uh going to be seen in the central canal right down the center of the spinal cord but also surrounding the spinal cord in this region here the sub-arachnoid space um i want to point out something else here um the subdural space will be between the dura and the arachnoid matter but this region here between the bone the vertebra and the the dura mater this region here is called the epidural space and this is is unique it does contain a lot of adipose tissue which are which acts as a protective barrier uh protecting the spinal cord from um any kind of trauma as it um kind of comes in contact with the with the bony vertebra so it acts an additional it offers i'm sorry an additional level of cushioning or protection uh between the bone uh the bony vertebra and the and the spinal cord okay now what i want to point out here is um and again i'll i'll again go over this in in a subsequent slide there are um two roots here um so this root is called the dorsal root okay and this la this enlarged region here is called the dorsal root ganglion the dorsal root uh is part of the spinal nerve bringing in sensory information from the rest of the body from the peripheral organs like the skin and skeletal muscles and joint receptors and anything related to like touch vibrations pressure uh pain temperature um positions of your of the joint uh stretches in in relation to skeletal muscle all all of that sensory information is carried in through that dorsal root right there and it kind of makes contact with the dorsal gray horn area up there okay now uh emerging from the ventral gray horn you have your ventral root which is right down there and this is going to carry motor information out of the spinal cord so dorsal is incoming towards the spinal cord bringing sensory information into the spinal cord whereas the ventral root carries motor information out of the spinal cord towards your say your skeletal muscles and so on and so forth now notice a little further down here the the dorsal root and the ventral root they both merge to form the spinal nerve remember i said the spinal nerves are paired so at this level of the vertebra um let's say let's say this is say cervical vertebra 3 for example so at this level of this of the of the vertebra you're gonna have two spinal nerves right there uh matched on both sides um that you would expect to see at that level of the vertebra and then obviously it's gonna you're gonna see the next pair uh below it and so on and so forth so this is how you um you end up with 31 pairs of spinal nerves and spinal nerves are considered mixed nerves and the reason for this is because like i just mentioned the dorsal root carries sensory information whereas the ventral root carries motor information so since it carries both sensory and motor information this is called a mixed nerve okay i think i've talked about everything that i needed to discuss here so let's go forward um like i was pointing out on that previous slide um cross section of this of the spinal cord uh resembles a butterfly or the letter h yeah that's another way to think about it let me back up yep that kind of looks like the letter h right there um i prefer i guess the butterfly resemblance because i can point to those top regions as the butterfly wings and i know that the butterfly wings always always points towards the the posterior or the dorsal aspect of the spinal cord and the vertebra okay but you can also think about it as a letter h um and remember we talked about uh the gray matter consists of three different um gray horns the dorsal greyhound this is always going to receive sensory input and i'll i'll show you this is actually broken down into two different regions it can receive sensory inputs from the somatic regions like anything related to the skeletal muscle and anything else from other visceral sensory inputs um like the skin and and so on and so forth would all of those sensory inputs would be received in the dorsal greyhound region remember we said the ventral greyhound this is mostly motor output so this is motor output most specifically somatic motor output so this is information that's been carried out of the spinal cord towards the skeletal muscles to direct um contraction and relaxation of those skeletal muscles so that would be somatic motor outputs so what was the importance of the lateral greyhound then you're only going to see a lateral greyhorn in the thoracic and in the upper lumbar regions um because this the outputs coming out of the lateral gray horn is related to the autonomic nervous system which controls involuntary targets like uh cardiac muscle uh smooth muscle and then secretions from from glands okay so let me back up to repeat this one more time the dorsal greyhound is going to receive sensory inputs from with the help of that through that um dorsal root is going to carry sensory inputs from both the somatic and the visceral regions um those the ventral root right there that's going i'm sorry the ventral gray horn that's going to carry motor output specifically to this skeletal muscle somatic motor output whereas the neurons are originating from the um lateral gray horn region that's going to be important for carrying motor outputs again but except it's not somatic motor outputs it doesn't have anything to do with the voluntary divisions it controls automat autonomic um outputs like um involuntary targets like cardiac and smooth muscle okay so make sure you all know this this is super important uh three different gray horns and uh what's the the relevance or the functions of those different regions so what's receiving uh sensory inputs and the the other two regions sending out motor outputs but to which specific regions ventral always for somatic and lateral for the autonomic um motor outputs um i already discussed this on that previous slide where we talked about the two different roots there are two roots right you have the dorsal root that's carrying sensory information towards the spinal cord and the ventral root which is leaving the spinal cord carrying output motor information out of the spinal cord and the two roots together combine to form your spinal nerve okay the dorsal root ganglion this is where this is related to your dorsal root this is where all the cell bodies of your sensory neurons so like the soma the cell bodies of your sensory uh neurons is normally mostly unipolar neurons um all those cell bodies accumulate in this dorsal root ganglion region okay so here is a different view of the cross-section of the spinal cord uh what's missing here is the the bony vertebra surrounding the spinal cord this is just a close-up of the spinal cord and so what you're seeing here is um i guess three levels of the spinal cord if you will so you could imagine that maybe that is cervical vertebra three and so this region here would be cervical vertebra four cervical vertebra five so on and so forth so every obviously it's a continuous spinal cord but you're gonna refer to the spinal cord and the nerves the spinal nerves emerging from each region of the spinal cord based on the vertebra that it is associated with okay so i'm just going to kind of simplify it here and kind of give you some reference so let's say those are the c3 spinal nerves and here's my cervical uh spinal nerves at the level four and here's my c5 okay that could be an example now remember at every level of the spinal cord you're gonna have um a pair of spinal nerves so on both sides okay okay looking at your uh spinal cord again i want to point out uh centrally located that's the central canal uh that's where you're gonna see csf throwing through that central canal you're seeing the gray matter here you know remember those butterfly wings uh that's gonna be the dorsal greyhound the lateral greyhound on the side and the ventral gray horn here on on the bottom um all of these regions here uh this is going to be your white matter the lighter portion to match your gray horns okay so greyhounds are all listed here uh dorsal on the top lateral on the side and of course ventral towards the bottom there to match these gray horns you're going to have white columns which is which is related to the white matter regions and lighter regions this is also called funiculi or funiculus so again remember this portion here should be facing the dorsal aspect and this portion here faces the the um the ventral aspect so you've got your dorsal funiculus the lateral funiculus right there and this should be your ventral funiculus on both sides of the spinal cord okay so both of those are dorsal funiculi on the left on the right you have your lateral funiculus and then here on the bottom here that's your ventral funiculus okay so you have matched regions between your your gray your gray matter regions and your white columns okay uh coming back to those nerves um this is a spinal nerve so see say your c3 spinal nerve and here's the other matched the pair uh of the other c3 spinal nerve on each side you're going to have all of your sensory information being carried in through the dorsal root so that that's where it kind of fans out into these multiple branches that's your dorsal root making contact with the dorsal gray horn on the top same way there here's a dorsal root making contact with the dorsal gray horn right there um carrying motor information out of the spinal cord you fro especially let's say from the the ventral gray horn you have your ventral root right here so and right there carrying motor information out of the spinal cord the dorsal and the ventral roots on both sides each of those roots will combine together to form the spinal nerve on that side of the spinal cord okay um this enlarged region here this is what we call the the dorsal root ganglion right there okay this is where you see the the cell bodies of all of these incoming unipolar sensory neurons all the cell bodies accumulate in that enlarged region um the other thing i want to point out here are those uh the spinal meninges so if that's the spinal cord then this whitish layer that you're kind of seeing directly in contact with the spinal cord should be the innermost peer matter then you've got your uh your spider web kind of looking middle layer which is your arachnoid matter and the outermost the thickest the most robust layer which is your dura mater so where is the sub-arachnoid space it should be in between the pier and the arachnoid matter and the relevance of that sub-arachnoid space is that you also see csf in those regions okay so here is uh i guess like the final view of the cross section of the spinal cord um again to orient yourself here's the central canal all of the white matter on the outside here's the gray matter on the inside remember that's the dorsal greyhound uh you've got your ventral i'm sorry your lateral greyhound and your ventral greyhound down here and it's kind of designated remember we said um the dorsal greyhound is going to receive information through the dorsal root right there this is sensory information so i've broken this down as ss and vs ss is somatic sensory which is carrying sensory information only from the skeletal uh muscle region and the bs is uh sensory neurons but from other viscera other visceral sensory neurons both of those sensory neurons have to um be all of the the processes of those sensory neurons are carried in through that dorsal root and it's going to make contact with that dorsal gray horn right there so that's going to be somatic sensory and visceral sensory uh your lateral gray horn shown here in yellow lateral gray horn is going to be where you have motor output but this is carrying information to the involuntary targets so this is ans targets that's why these are called autonomic neurons or visceral motor neurons bm okay your um ventral gray horn right there we shown an orange that's going to carry modern information out but this is only targeting uh ss for somatic which stands which is related to the skeletal muscle again so remember your dorsal greyhound this is only for sensory inputs sensory neurons from both somatic and visceral um your lateral gray horn is is only for motor outputs but specifically visceral motor meaning carrying information to the autonomic nervous system targets and your ventral gray horn is for carrying information motor outputs specifically to the somatic region so like this is your skeletal voluntary motor neurons okay so i think um i think i've covered uh the different grey horns and the importance of those greyhounds make sure you know the dorsal root versus the ventral root and again remember both those roots emerge to form your spinal nerves on both sides okay okay so now that we've talked about the the gray matter so we kind of focus quite a bit on all of this right we talked about the main regions here and which one's sensory versus which ones are a motor now i'm going to turn my attention to all of this on the outside the the lighter region on the outside which is your white matter that's your um your your white columns or your or your funicula your funiculus so white matter um this is uh remember gray matter always this is mostly um non-myelinated um dendrites and cell bodies and and smaller or shorter um axons that are non-myelinated in the case of white matter this is mostly myelinated regions so mostly axon processes especially um long distance neurons and the the longer neurons with the longer axon processes so what i want to point out here is uh communication between the cns uh consisting of the brain and the spinal cord i've abbreviated spinal cord as sc right there so what's the communication between the brain and the spinal cord which is your which are your cns organs and the communication between those organs and the pns which is your peripheral nervous system everything else in your body every other organ and every other region of your body would be your peripheral nervous system all of these communications are carried out through a set of nerves um cranial nerves if they are associated with the brain and spinal nerves if they are associated with the spinal cord okay so when you think about what the white matter does this is basically it it it allows for communication between one it could be different regions of the brain and or it could be between the brain through the spinal cord but connecting it with the peripheral pns the piano the peripheral nervous system so i'm want to define three different um examples of white matter and we always call this a white matter tract uh if you recall a tract is basically a collection of axon processes okay um so let's start with uh let's start with transverse actually so transverse is if you remember the brain has a a left and a right cerebral hemisphere so communication between the left and the right cerebral hemispheres as you can kind of see by my orange arrow right there that would be a transverse tract uh specifically called commiseral fibers okay if i'm talking about communication between the brain and the spinal cord to your peripheral nervous system this would be going from the cns downwards or out of the cns towards the peripheral nervous system this is called a descending tract okay so descending because i'm carrying output information from the brain and the spinal cord into whichever target organ or effector related with the pns now right the opposite if i'm carrying sensory information from a peripheral receptor like say on the skin or the skeletal muscle or the joints carrying that sensory information upwards towards the brain and the spinal cord that would be ascending tract okay so remember brain and spinal cords outwards to towards the peripheral nervous system is a descending drag and carrying information from the pns towards the brain of the spinal cord is an ascending tract okay and transverse commensural fibers are communication white matter tracks between only within the brain but between the left and the right side of the cerebral hemispheres okay i already discussed this uh the white matter is organized as three different white columns of funiculi you have your dorsal your lateral and your ventral funiculi and kind of to match your grave your gray horns okay so what i want to do is point this out here using this schematic so your gray matter um again that's going to be the dorsal aspect and here's your ventral aspect um the gray matter shown here in this darker region central canal right there right there in the center the white matter is shown here on the outside the lighter region okay so i want to show you the different um columns okay so of course your your white matter your this is going to be your your dorsal um funiculi you have your lateral funicula here on the on the sides and then this would be your ventral funicula so what i want to point out is let me back up uh kind of show you examples of ascending and descending tracts transverse is really just communication within the brain from one side to the neck to the other side i might want i really want to focus on an ascending track and a descending track and give you information i'll give you examples of some some of these tracks okay so let me let me get back to my schematic here so i have here on the left uh different examples of ascending tracks and on the right you see examples of descending tracks so remember what is an ascending track a sending track is carrying information sensory information from the peripheral nervous system it's ascending it's moving upwards towards your brain and your spinal cord of course you're looking at the spinal cord here okay so an ascending tract would be from a peripheral target or from a lower region towards the upper brain regions or towards the spinal cord the descending tract is right the opposite is carrying motor information out of the brain the spinal cord but downwards towards the rest of the body okay so let's give some examples of ascending tracts here and these are very important so these regions right here obviously you're going to have matched tracks on both sides of the spinal cord so if i focus on just one half of the spinal cord you would assume that whatever i'm discussing here in terms of an ascending tract or a descending tract you're going to see a matched a paired tract on the other side of the spinal cord okay so i'm going to focus here on this region this is your dorsal finiculi your dorsal white column there are actually two specific tracks here uh towards the median aspect of that spinal cord um this region here is called the fasciculus chrysalis and this outer region here is the fasciculus cuniatus both of them together play a huge role in kind of in working towards the medial lemniscule tract and i'm going to give you that example here in just a little bit remember these are all sensory tracks meaning as information is flowing um through these tracks this is carrying sensory information towards a higher brain region uh sensory information like what like uh touch and pressure vibrations and um relation to in relation to uh what we call a proprioceptor which is giving information related to muscle stretch or information from a joint um giving information related to to not not just stretch but also but like a tension that's developed so uh those are all sensory information that's being carried um uh not not necessarily just the the the gracilis and the cuny artists but those are all examples of information that's carried through an ascending track so specifically here pointing out the two important uh tracks here really related to the medial and missile pathways and i'll go into some details just a little bit so you have your gracilis track right there which is uh towards the middle and towards the lateral aspect you see the puny artist okay and then there are other tracks that are kind of shown over here you have your spinosa cerebellar tracks um kind of shown here um you you won't need to identify any of these tracks on your lecture exam on a lab exam you're going to be required to point out these two the gracilis and the cuny artists but what i want you to know here is how does an ascending tract work how is information transferred from one region to a different region and likewise what is a descending tract and how is information transferred from in a descending tract we're going to define different types of neurons in just a little bit and here on the bottom are examples of kind of the the spinothalmic tract so these three tracks here uh the dorsal white column consisting of the gracilis and the cuneiros that's one important ascending tract the second important tract uh is your spinothalamic tract and the third tract is your spinosa rebella uh tract so i want to point out uh let's look at like this the spinous cerebellar tract or your spinal thalamic tract for example always when you're looking at that tracked information or the name of it the first part is where this tract is originating from okay so this is my source so that tells me it's originating from the spinal cord spinal okay and the second part of this in the name cerebellar tells me that this is where the tract is ultimately going to end up so the destination the two part is is the uh is the sec is the second part of that name so the first part is the source of this track so from it's originating from the spinal cord and the second part of the name gives me information on where that tract ends up or where is the destination so it's going to the cerebellum so it's originating from the spinal cord but it's moving upwards into a brain region called the cerebellum right that's why this is an ascending tract because it's from a lower region the spinal cord but moving upwards into a a higher brain region okay which um so those are the examples of ascending tracks on the right you're looking at examples of um descending tracks and there are several different descending tracks here i am mostly going to focus on what you see highlighted over here this is the the pyramidal track which is also called the corticospinal tract same thing with respect to the designation of that name and how to make sense of it the first part tells me where that track begins from so this is from the cortico cortical as in the cerebral cortex so this actually is beginning from the brain and it's going towards and it's going to the destination is going to be in the spinal cord so from a higher brain region to the spinal cord that's why this is a descending tract okay um again like i said i'm only going to focus on these two right here which is your corticospinal tracts uh there are different uh examples of other descending tracts like your reticular spinal tract your rubra spinal tract the vestibular spinal tract the tectospinal tract so i'm not going to go into those details as much okay i'm going to really focus on the dorsal white column for an example of the ascending track i do want to point out the spinosa regular tract as well to a little bit to a certain extent and when it comes to the descending track i'm going to be focusing on the pyramidal tracks so let's get started with some overall features of any kind of uh white matter track and then go into some details for each of these tracks okay um before i go into our discussion of ascending and descending tracks let's discuss some spinal cord um disorders and then we'll go into the the actual discussion of an ascending tract and a descending tract so there's several different disorders related to spinal cord trauma um so this really depends on whether this is um a damage to the spinal nerve but is it the spinal is it the dorsal root that's damaged or is it the ventral root that's damaged so when there's damage to the the sensory uh information so like the sensory track that's being carried through the dorsal root this is called paresthesias uh so obviously this is going to affect uh sensory motor i'm sorry sensory function or loss of sensory function is what's going to end up being if it's a damage to a motor region so your ventral root then this is obviously going to result in paralysis because this is affecting motor function um transaction so let's talk about this if you see cross-sectioning of the spinal cord so damage of the spinal cord to where you're uh you are cutting or transactioning the the spinal cord this is going to obviously result in a loss of both motor and sensory function because of the information that's being carried in that region of the spinal cord this depends on which region uh is seeing this transaction so let's start with the the this this this term here paraplegia this is where you see a a cross sectioning of the span cord between the lower end of the spinal cord between um thoracic one all the way to l1 so if you see a damage to the spinal cord where you're seeing uh kind of like splicing of the spinal cord uh anywhere between the in the thoracic region to the very bottom of the spinal cord which if you recall ends at about l1 l2 anywhere in this region if you see damage of the spinal cord this is going to only affect the lower limbs and this condition is called paraplegia now if you go higher up on the spinal cord so anything where you see damage to the cervical region this can impact both upper and lower limbs resulting in quadriplegia okay um other spinal cord disorders um worth mentioning polio okay this is where you're seeing destruction of the ventral horn motor neuron so remember the ventral gray horn motor neurons that originate from the ventral gray horn which is obviously going to target the somatic motor region so therefore this is going to cause a loss of function to specific skeletal muscles depending on which motor neurons were impacted uh so this is where the polio virus affects these um these motor neurons and causes damage of these ventral horn motor neurons obviously skeletal muscles will get damaged will undergo atrophy and they'll start up kind of start withering away of course this is going to ultimately affect respiratory muscles causing paralysis and obviously if you cannot carry out respiratory function this is going to result in in death also affects the cardiac function als uh amitropic uh lateral sclerosis this is a this is a very um interesting uh spinal cord disorder and it's it's gaining a lot of um attention there are a lot of celebrities um who [Music] have uh succumbed to uh to als and so there's a lot of interest here related to understanding the pathology of this particular disease you may recognize the picture that you see here on the right this is a stephen hawking he was a very famous english physicist a very great zionist and an extraordinary man whose work and legacy will live on for many many years he was diagnosed with als at about age 20 21 and typically most als patients they have a very short prognosis after after they are diagnosed with it typically death would occur within five years but stephen hawking he beat the odds and he he he was diagnosed with it at about 2021 but he ultimately died at the age of 76 so um his his perseverance and with with his brilliance uh inspired people all across the world and it never slowed him down to where um he he really did accomplish a lot of wonderful things and has been able to crack so many different things related to physics concepts so in the case of als what stephen hawking had and what many many people do have is a is a very slow slowly progressing uh condition of course in most cases this this would progress and leading to death within five years um this scientist stephen hawking had something that was a little more like a slower form of uh deterioration of als which ultimately uh takes uh takes control of the body and makes it uh much harder to to breathe to to carry on normal functions um he lost his voice and it was a slow progressing condition so what what happens here is um we don't quite understand the pathology of this disease we do know it causes uh destruction of your ventral horn motor neurons so again this is going to impact all of your somatic motor functions uh related to a particular descending tract called the the pyramidal track which i'm going to explain here in one of my subsequent slides uh so ultimately because you are affecting motor function and you you're destroying motor neurons from the ventral horn area this is what's ultimately going to affect muscles in different parts of your body resulting in ultimately death um we are trying to understand the pathology of this of this particular disorder we think that there could be genetic mutations um that are causing this disorder but there's a lot more that we need to understand and explore okay um so let's move on to talk about um those those different pathways that i was discussing a while ago i want to focus on some examples of ascending and descending pathways but regardless of what type of neuronal pathway we're talking about there are certain features that are common to any tract or to any pathway related to the white matter i do want to point out these four features here uh decursation so this is typically where um pathways will cross over from one side to the other side at some point and i'll give you an example and i think this will make sense so like for example sensory information um being carried safe from your your left foot okay so say you you you step on a sharp object so pain related information or temperature or whatever so sensory information from a left peripheral organ so say your left foot ultimately is processed um in the somatosensory cortex region of the brain but uh it's going to be processed in the in the opposite region so information from the left foot is processed in the uh right cerebral hemisphere within the within the somatosensory cortex so this is what we called it has to kind of cross over left to right or right to left and this is called decoration and i'll show you examples of where that happens a relay when you're thinking about a pathway a neuronal pathway this always consists of a chain of neurons normally two to three neurons depending on which pathway we are referring to somatotopy um so precise regions um in terms of like spatial relationships within the cns uh very specific regions of the somatosensory cortex will receive information sensory information from um let's say the lower limb versus the upper limb or from the from the face region um so very it so sensory information from very specific regions of your body are mapped spatially on very specific regions of the cerebral cortex okay and this and the same that you would say for your motor regions as well this is what we call somatotopic and symmetry always you have paired tracks you always have a left and a right track so i'm going to actually show you some examples and hopefully this this concept of decoration uh and symmetry will make sense okay so let's let's start with ascending pathways uh so remember this is ascending towards the brain and the spinal cord from the peripheral nervous system so this always consists of typically consists of a chain of three different neurons you have your first your second and your third order neurons this is really important for you to understand and i have this drawn out in a subsequent slide as well so i'm just going to quickly explain it here on this slide and then use a schematic to to kind of pull all of those uh features together okay so your first order neuron this is going to begin from some kind of receptor within the within the peripheral nervous system so let's say a cutaneous receptor so like a sensory receptor on the skin or it could be a proprioceptor this is information uh this is a receptor on um say the skeletal muscle or like in the joint cavity so these are carrying sensory inputs from these receptors in the peripheral nervous system and this this first neuron is is what we call a first order neuron it's going to take this information to typically depending on the tract typically the spinal cord or the medulla oblongata which is a part of the brain stem this is where that first order neuron will synapse okay it's going to form a chemical synapse uh with a second order neuron so the second so the first and the second order neurons are going to meet up right here at at the spinal cord or the medullary and leaving say the medulla leaving out of the medulla you have your second order neuron which would then go all the way up to a higher brain region typically the thalamus or the cerebellum so if if it synapses at this at the thalamus this is where the second order will meet the third order neuron and in the thalamus region and then that third order neuron leaving the thalamus will then ultimately extend all the way into the cerebral cortex and since this is carrying sensory information this is going to go to a very specific region in the parietal lobe on the post central gyrus called the somatosensory cortex region this is on the parietal lobe okay um if if we are talking about a second order neuron uh that takes information into the cerebellum normally this is your final destination so there typically is no third order neuron if you're referring to the cerebellum this is going to make sense when i show you a schematic and show you where you see the first second and the third order neuron okay here are some three different examples of your ascending pathways which i also discussed on a previous slide um there's three main sensory pathways carrying information you have your dorsal column medial laminiscal pathway which is what i'm going to talk about yes that's quite a mouthful but this is not too complicated i'm going to explain it i'm going to break it down for you so that's your first sensory pathways the dorsal column medial lemniscular pathway um [Music] the second pathway is the spinophthalmic pathway so this is from the spinal cord towards the thalamus region of your brain um most of these pathways here they're carrying information related touch vibrations pain temperature again course touch in this case pressure so on and so forth and your third pathway is this right here the spinous cerebellar pathway which is from the spinal cord to the cerebellum uh this is always carrying information if it's terminating in the cerebellum this is going to carry information from different proprioceptors which are mechanical receptors carrying information related to muscle stretch or muscle tension so your muscle spindle would be an example of a sensory receptor in the muscle in the skeletal muscle in the peripheral nervous system carrying information related to stretch of that skeletal muscle up towards the cerebellum where you're gonna the cerebellum makes sense of uh what the coordinates are and what is your position in relation to um x y z coordinates and like how do you maintain balance and so on and so forth so what i'm going to kind of go into some details is pathway number one which is your medial lemniscle pathway this is important for touch and vibrations and i'm also going to quickly explain the spinosaure bella pathway which is carrying information from say the skeletal muscle via this receptor the muscle spindle carrying it all the way to the cerebellum and this would be in relation to uh muscle stretch to for you to maintain proper balance okay so let's start with the dorsal uh dorsal column medial laminiscal pathway this is for touch and vibrations like i mentioned this consists of two paired tracks you have your gracilis and your uh cuneotis um pathways and i'm going to explain this to you using this schematic okay so i'm going to start with the bottom and work my way towards the top because this is an ascending pathway so the information is it starts from some peripheral organs so i'm kind of showing you cutaneous receptors for touch and your joint stretch receptors there again so these this is this is from the foot from the hand whatever i'm going to work my way from the bottom towards the top but i'm going to stick to this pathway here this darker pathway here this is my docile a medial laminiscal pathway the lighter blue pathway here on the left this is going to be an example of the spinous cerebellar pathway so i'm going to start with this first here on the right okay the laminar scale pathway so what what you're seeing here is some sensory information from say the foot region or from the the upper limb the hand the palm region whatever sensory information related to touch vibrations related to tension in the joint region all of this is carried um through a first order neuron so i also have it kind of shown here on on the right so it begins with the pns receptor like the foot or the other the hand so these are different receptors touch receptors joint stretch receptors begins here and you have a first order neuron carrying this information upwards either towards the spinal cord or the medulla oblongata okay so that's where the first order neuron ends then from the since i'm following through with the right here i'm going to take this all the way to this medulla oblongata this is where the first oral neuron synapses with the second order neuron so exiting the medulla you would see a second order neuron which takes all of that information towards the brain either in the thalamus of the cerebellum if you're taking information into the cerebellum it ends right there so the second order neuron terminates right there at the cerebellum that's the end of that pathway but if i'm talking about like the landscape pathway this is where the second order neuron synapses in the thalamus and it meets up with a third order neuron and that third order neuron was going to take that final information remember this is sensory information related to touch or stretch and so on and so forth so you're going to carry all of that information towards uh the somatosensory cortex region within the cerebral cortex this is on the parietal lobe okay so working my way from the bottom towards the very top here the top should be the the cerebral cortex specifically the somatosensory cortex region within the parietal law so this is a first-order neuron carrying this sensory information from um the foot uh or in this case the the hand carrying this through the spinal cord okay so you can see it shown here as two different tracks the fasciculus gracilis if it's from the lower regions like the foot versus the fasciculus cuny artists if it's from the um the upper regions of the spinal cord like the cervical regions which would be related to your upper limbs and so regardless you have your fasciculus curias or the all your fasciculus gracilis but this is all a first order neuron carrying this information through the spinal cord different regions of the spinal cord cervical up here lumbar down here okay and that first order neuron remember it carries that information where to the medulla in this case so i'm going to carry it all the way up here this is the medulla bengata which is the uh a part of the brain stem okay so this is where you're seeing synapse occurring where that first order neuron synapses and picks up your second order neuron right there so that's what's happening right here i do want to point out here typically in the region of the medulla oblongata is where you see this concept of decussation so if you're following along with me let's say this is the the right side of the body let's say that's the right right foot or the right hand i'm carrying all this information through my first order neuron it's synapsing right there um in the in the medulla oblongata so the right side of the medulla oblongata and notice what's happening here it's crossing over that that pathway kind of crosses over from the right to the left this is what we call decussation now everything is carried through the left side of all of these different brain regions so i'm going to go up remember right right on top of the medulla you should see the pons and the and the midbrain region so i'm not gonna there is no there is no um synapse here so we're talking about a second order neuron right here in the in the medulla you have to carry it all the way up to the thalamus region so no no more synapse it's going to go all the way up here it's going to bypass the cerebellum and and all of that the midbrain right here till it gets into the cerebral cortex and here's your thalamus region towards the middle so this is where it's synapsing so that's my second order neuron in the thalamus synapsing where it picks up my third order neuron that's the last part the third order neuron carries this information specifically to the somatosensory cortex region within the parietal lobe okay so first order is from the peripheral receptor um all the way up into the medulla oblongata this is where it picks up it synapses with a second order neuron and carries all of that information up that's the second order neuron synapsing here in the thalamus picking up my third order neuron okay so this is again we talked about a relay of of neurons you know in this case in an ascending tract you have what i've explained here is a first to a second to a third or a neuron okay uh now remember we said okay so this is say this is information this is sensory touch information related to the right foot remember it is going to cross over here and it's going to be processed on the left cerebral cortex this is what we called a decussation right this is a kind of a contralateral arrangement to where you are processing information in the opposite side of the brain again specifically in the somatosensory cortex okay um this uh this where you pick up your second order neuron this is what we call the medial lemnischel tract but it's kind of associated with your white matter columns your fasciculi related to the cuneiatus and the um the graceless okay which is part of the spinal cord okay all right so what i want to point out here is this light blue tract here on the left okay so this is an example of a spinous cerebellar pathway so begins with the spinal cord and i'm carrying this sensory information uh towards the cerebellum right here okay now this only consists of two neurons so my first order neuron begins here uh at the receptor in the peripheral nervous system on the muscle spin on the skeletal muscle called this muscle spindle and carrying that information through the spinal cord okay so this is where so instead of synapsing at the medulla it's synapsing here at the at the spinal cord so that's my first starter neuron synapsing right there picking up my second or a neuron and that's going to go all the way it's going to bypass the medulla um the the pons and all of that and it's going to go straight up here to the cerebellum where you're processing that information related to that skeletal muscle that that sensory information is being processed by the cerebellum and because it's a cerebellum here this is the second order neuron has already reached its destination so it doesn't pick up a third order neuron so an ascending tract could have either two neurons or three neurons okay so those are two important ascending tracts so that's important for you to know those details okay so let's talk about descending tracks to uh to wrap up our discussion of uh the brain and the spinal cord here um the descending tract this is carrying motor information motor output information from the brain and the spinal cord uh basically towards the effectors that it needs to control within the peripheral nervous system like the skeletal muscles this consists of only two neurons you we're going to talk about upper motor neurons and lower motor neurons specifically the upper motor neurons originate from the primary motor cortex within the frontal lobe those specific neurons are called pyramidal cells that's why um one of your descending tracts also goes by the name pyramidal tract uh that's because it is related to your upper motor neurons within the pyramidal pyramidal cells okay so let me point this out to you and give you an example of your pyramidal pathways um this is an explanation of of the entire pathway this is also the pyramidal tract is also called the corticospinal because it begins in the primary motor cortex within the cerebral i'm sorry within the cerebral cortex and it carries that motor information towards the spinal cord i'll show you where you expect to see the uh would you call it um the upper motor neurons and the lower motor neurons let's just use this schematic to uh put this into perspective so now we're talking about a descending track so i'm talking about uh it originating in the cerebral cortex and moving outwards towards the the peripheral nervous system so let's look at my schematic here um primary motor cortex that's where this tractor originates uh the very first neuron is called an upper motor neuron it's going to take that information all the way to the spinal cord where it then synapses with a lower motor neuron and then the lower motor neuron is carries that information to your final pns effector so this is your lateral and your ventral corticospinal pathways i'm just going to follow through with let's say the right side here and show you what's going on so uh within the primary motor cortex region uh you there are these specific pyramidal cells this is where you have your upper motor neurons right there starting from here and there's no more synapses it's going to go all the way through the brain stem region medulla oblongata which is also brain stem and depending on where i'm carrying this information so normally in the medulla is where decoration occurs so notice how you go from the let's say the right side right here it's going to cross over and move to the left side of the spinal cord and then here you're seeing it in the lumbar spinal cord that's where you're seeing it um meet up or synapse with your lower order neuron and that's carrying information through from via the spinal cord that lower motor neurons carry information to your ultimate pns target namely your skeletal muscle so this is obviously for motor output to help control that skeletal muscle to bring about uh say for example contraction okay uh again i want to point out here this is this is pretty straightforward you just have an upper motor neuron synapsing somewhere on the spinal cord where it picks up a lower modern neuron okay um here on the on the left you're seeing the the paired corticospinal tract again this is carrying information from let's say the left and then it kind of hops over here so that's where it's controlling the right side of the body okay so it's always going to be contra lateral control uh of the body uh between the peripheral target and the brain region so that in essence kind of wraps up our discussion of ascending and descending tracts so what we did in this lecture is talk about higher brain auto brain functions like we talked about the reticular formation and the limbic brain we talked about memory and brain waves consciousness all of that we talked about the blood-brain barrier that's an important concept of meninges which offers protection to the brain and the spinal cord and then we really went into our discussion of the spinal cord where we discussed the overall anatomy of the spinal cord the the the gray horns the the white columns all of that and then we talked about the functions of each of these different regions um and then we talked about spinal nerves 31 pairs of mixed nerves and then finally um we concluded this particular chapter on the cns discussing ascending and descending tracks so that really just wraps up the central nervous system i hope this was useful and i hope this made sense to you thank you