okay good morning everybody welcome back uh we are going to uh use this time to uh move right along in our uh nervous system topic uh where we left off we were um learning about the uh anatomy of the brain and uh the last piece on on this topic um is uh going to relate to structures that come out of the brain but are technically part of the peripheral nervous system uh we see that they are highlighted in this yellow color that goes along with our previous images where the central nervous system was in Gray and then the peripheral nervous system was in uh the yellow color uh so this is the first of the peripheral nerves uh these are called cranial nerves what's special about the cranial nerves is that these are nerves that come directly out of the brain where the rest of the peripheral nerves will come out of the spinal cord we have uh 12 pairs of cranial nerves uh so uh 12 on each side of the brain and uh we see that the cranial nerves are going to have a variety of functions uh both uh sensory motor or a combination of both sensory and motor um the cranial nerves are a significant uh topic because these are something that uh are tested clinically as a way to uh check for signs of uh potential harm to the brain as a result of things like strokes and aneurysms um what we see here is that these nerves are all clustered on this uh inferior uh portion of the brain and uh there are uh blood vessels that travel right along this area here so if there's damage to the blood vessels one of the early things to show uh symptoms of that injury are the cranial nerves so uh checking the cranial nerves clinically is a way to determine whether a person is uh in need of further evaluation so take for example a patient who has very severe headaches and you want to know is this is this headache potentially a sign of something worse like a developing aneurysm uh well you do a quick cranial nerve screen to find out um cranial nerve screening is great because it's something that a skilled health care provider is able to perform in about one minute um so if they have all the equipment ready they can jump right into doing this screening uh first of all cranial nerve one is a sense of smell so you just have a vial of coffee go you know what's that smell like it smells like coffee okay cranial nerve one intact next one is cranial nerve two uh this we check by uh shining the pen light in uh the person's eyes and looking for the pupilary reflex that we'll learn about in an upcoming lab um cranial nerves uh three four and six are all involved in eye movement so this is where we take that same pen light we just say follow the light with your eyes you know and show that the eyes move synchronously with one another uh cranial nerve five is uh the sense of sensation on the face so you just touch the face in these three areas and say do these feel the same on each side um cranial nerve 7 is uh the muscles of facial expression so you have the person close their eyes and keep them close as you try to open them you have them um puff out their cheeks and hold air and without the air puffing out those are testing the orbicularis ocula and orbicularis orus you have the person shrug well raise their eyebrows testing the frontalis muscle showing that the muscles of facial expression are working equally on both sides then we have cranial eight that you just uh uh test the ability to hear with just a little bit of rubbing of the fingers next to the ears cranial nerves nine and 10 are involved in the gag reflex so you have the person open wide say ah you look for the movement of the uula and then you gag them with the little uh tongue depressor um finally uh cranial nerves the cranial nerve 11 is involved in the um skeletal muscles of the uh upper trapezius and sternal clom mastoid you have the person shrug their shoulders push down make sure they can hold the shoulders up have them turn their head against your hand showing that they've got strength on the sternomastoid finally cranial nerve 12 is movement of the tongue so you have the person um stick their tongue to each cheek making sure that they got some strength to the tongue movement stick the tongue out straight and make sure that it doesn't deviate to one side so you can go right through those tests and look for any signs of impairment to the cranial nerves and if you find impairment for example the tongue the person sticks out and it goes you know then that's a person that you would refer for further evaluation uh due to concerns that there might be uh damage to uh the blood supply to the brain okay um you are not responsible for learning these terms the names here so you have the list of the cranial nerves you do want to know that there are 12 on each side but you don't need to know for example that cranial nerve 10 is the Vagas nerve um that being said we do have this for you here so uh so it's good to know that it's the Vegas nerve in order for that joke to make any sense anyway um so with that we are going to move on to our next structure in the uh central nervous system and that is the spinal cord uh the spinal cord uh has these three functions conduction carrying the information uh up to the brain from the body and down uh to the body from the brain Locomotion is a very interesting thing here uh what we see here is that uh the repetitive motions of walking um are controlled by uh the spinal cord okay so when you are walking you do not have to think about walking as long as the the walk that you're doing is uh is predictable so let's say you're walking on a track the ground is the same with each step that walk is all under the control of the spinal cord so then it frees your brain up to do other things you know you can look at your environment you can think about you know what you're going to do uh you can uh perform other actions you know you can look at your cell phone all that stuff you're able to do all this um with your brain while your spinal cord controls putting one foot in front of the other um but then your brain comes in if something needs to be changed so you're about to put that foot down and you see that there's a patch of ice well your brain is going to say okay wait a minute nope don't put the foot there put the foot off to the side so you miss that ice so the brain um overrides the spinal cord but the spinal cord is there to do the majority of the work when it comes to controlling your normal walking gate um reflexes we're going to uh end today's lecture learning more about reflexes and we're going to show why the spinal cord is part of the central nervous system because the spinal cord is what ultimately makes the decision about uh triggering a reflex so telling the body what to do in response to a stimulus so looking at the anatomy of the spinal cord first of all it begins up at the frame and Magnum where it uh has connected to the uh medulla portion of the brain then travels all the way down to the spinal cord level L1 so it does not go down the entire length of the uh of the spinal column because we see the cord itself ends at about L1 and then what travels through the rest of the uh Lumbar and sacral and coxal regions are individual nerves so it's no longer the solid cord the uh spinal cord is anchored at with the uh terminal philm so we go to this image here to show that after the cord ends uh there is this uh material that's going to connect the uh spinal cord at the inferior end uh so then that way the chord is you want to think of it being like a guitar string it's connected to the brain it's connected to the sacral region it is anchored at both ends so it's not flopping around inside of the vertebral column where the cord ends uh is where we then form our next structure called the Cina which uh is Latin for horse's tail and the horse's tail is uh the uh nerves that we see here in the lumbar and sacral and coxal region uh so this looks like a horse's tail where the tail ends and then you have all the long hairs of a horse's tail those long hairs are the individual nerves in this region I will point out the Cina is a term that you'll hear in the future uh as it's uh there's a condition relating to it called cinus syndrome which is uh when a person suffers injury to uh the uh individual nerves in this region as a result of for example a space occupying lesion like uh a severe disc herniation or the development of a tumor where uh these nerves become compressed cardinus syndrome is a surgical emergency so this is the person who uh comes into the doctor's office and says that they have not urinated for a day and a half uh they've not had a bowel movement for um you know several days and it's because these nerves are uh being impinged and they're losing uh control of either their bladder B okay um we see the location of the spinal cord how it's going to run down this vertebral column through the uh vertebral uh framen of each vertebrae uh so it'll come down and travel through the uh that uh Canal that's created as we stack the vertebrae on top of one another and the next thing is uh the uh meninges which are going to be a protective coat that surrounds uh both the brain and spinal cord uh the meninges uh we see are uh these uh fibrous layers wrapped around the spinal cord but then when we look at the brain we see the same fibr layers around the brain we have three layers of the mines all of them have the uh second name mat which is Latin for mother okay so the menis are a protective mother basically they are sheath surrounding the central nervous system the brain and spinal cord they're a protective mother swaddling the uh the the child that is the nervous system so our first layer the dura mat dur think durable this is the outermost layer it's the durable layer it is a tough fibrous material that is the outermost layer we see it is this uh light blue color here it's the outermost layer when we look at uh this image here the the dura is the outermost layer of the meninges inside of the dura we have the arachnoid mat and arachnoid refers to spider so this one uh has spiderweb like uh connective tissue fibers um that open up space for the what we see the simple squamous epithelial cells uh to uh produce the um cerebral spinal fluid that fills the subarachnoid space what we're seeing here the arachnoid monitor is this purple layer and sub arachnoid underneath the arachnoid layer we see this blue fluid that blue fluid is shown here that blue fluid is the cerebros spinal fluid so the cerebros spinal fluid um surrounds the brain and spinal cord and not only surrounds it but even fills in the brain and spinal cord so we see this light blue fluid that surrounds the brain surrounds the spinal cord so the brain and spinal cord are floating in a cerebral spinal fluid bath but then it doesn't just around them it also fills them so we see these Open Spaces that get filled in with the cerebros spinal fluid so the brain has this fluid in particular in these structures called the ventricles we see these Hollow spaces in the brain that are filled in with cerebros spinal fluid what this does uh is it makes the brain more buoyant so by filling uh in the ventricles it helps the brain float in this cranial cavity this is something you guys probably haven't appreciated up to this point you looked at the skull but if you thought about it like could you imagine if the brain was just sitting in your skull just sitting on that bone and then what happens if you jump up and down your brain would go up and then come crashing down on that sharp and hard bone up and down up and down you just Mash your brain against your skull so the brain doesn't come in contact with the skull because it is surrounded by cerebros spinal fluid and filled with cerebros spinal fluid so it's just floating inside of the cranial cavity likewise the spinal cord uh has a hollow space that runs down the center of it that hollow space is um filled with the cerebral spinal fluid making uh the spinal cord once again more buoyant so it's just floating in that um vertebral Canal one final Point while we're talking about cerebros spinal fluid we see that in the lumbar region this is the the place where we sample cerebrospinal fluid and what's called the the spinal tap procedure so if we want to get a sample cerebral spinal fluid to look for signs of for example infection we would not go in the skull or in the uh cervical or thoracic regions because sticking a needle into these areas runs the risk of stabbing the brain or spinal cord but when you get down to the lumbar region there's there's no more cord remember it's now just individual uh nerves and so the Cina uh these individual nerves are are free to move so as we stick a needle into this space if the needle's about to hit one of those nerves well the nerve is just going to move it's going to get pushed out of the way by the needle as opposed to being penetrated by the needle so it's in this lower lumbar region that we perform spinal taps to sample uh cerebral spinal fluid and it's also in region that we perform epidural procedures so uh when a a pregnant woman is uh delivering a baby and needs the epidural for pain relief the injection occurs right here in the lumbar region as uh we we don't have the risk of stabbing the spinal cord okay final thing here when it comes to the menis is the deepest layer the pamat so p uh like Pious uh the loving caring uh uh mother the one that is in physical contact with the brain and spinal cord we have this innermost layer that is actually on the surface of the brain and spinal cord um and that finishes our three layers of the meninges um the meninges are something that we kind of forget about on a daily basis until uh we consider the condition menitis so menitis you add itis to a word and it means inflammation of the prefix so menitis would be inflammation of the meninges menitis is a potentially life-threatening condition depending upon what's causing the menitis um it's a common viral condition which is not really life-threatening uh but if it is bacterial or fungal menitis it is a life-threatening condition as we inflame the tissues surrounding the central nervous system so any questions so far about the spinal cord the ventricles cerebral spinal fluid uh the meninges okay good so we'll keep moving right along here um more on the spinal cord Anatomy we're going to look at the uh inside of the tissues here and see that the oh let me check on um so the question here um are nerves constantly moving or staying still I assume you refer you're referring to the codina so those um the free nerves that we've seen right now um those ones are u under tension okay so keep in mind that um that they are are anchored throughout our body they're adhering to tissues throughout our body so um nerves have a limited amount of Mobility to them um you certainly can move them just like you can move any other soft tissues like muscles and the fascia around the muscle um but at the same time they are also anchored they they come down and connect to the uh the muscles and um the tissues that they're they're um receiving sensory information from so their Mobility is very limited um so as you're sticking the needle in there they've got the mobility to you know shift a little bit but as far as like you know are are they going to move let's say laterally two or three inches they probably don't have that range of Mobility you want to think of it again like a guitar string where a guitar string um you know you can move it you know laterally you can move it kind of up and down uh but only a certain amount okay so our um two layers of uh tissue inside of the spinal cord we have the gray matter and the white matter uh these are referring to uh what we see here how if we do a cross-section of the spinal cord so we've cut through it and we're looking inside of it we see that the inside has this tissue that we refer to as the gray matter the outside has this tissue we call the white matter the gray matter is uh where we find the cell bodies of the neurons the white matter is where we find the axons that are wrapped in myelin so we'll learn about axons and myelin and all that um uh later in this chapter um but um what uh what we're saying here uh if you remember the nervous tissue the nervous tissue uh had a cell body that was the stellate cell body made it star-shaped right and then it had the long uh extension that came out of it called the Axon and the axon um was wrapped in supportive cells uh the supportive cells are what we call uh GLE cells and uh Schwan cells and all there's all sorts of different um supportive cells um but uh what I'm going to do is I'll I'll just show those cells like this so they're wrapped around the axon um these cells are uh high in lipids so this myelin is uh rich in lipids okay so this is the basis of what we're about to describe here the cell body does not have the U myin it does not have the the coat that is rich in lipids it's the axon that's covered in this coat of lipids so when we look at the spinal cord the uh organization of the spinal cord this is the spinal cord just running vertically um so this would be up toward your head this is down toward your butt the organization here of the spinal cord um is that uh the cell bodies are situated toward the center of the cord okay so the cell bodies are toward the center of the cord and then the axons that come out of the cell bodies um work their way laterally and travel up the edges of the spinal cord okay so this is the organization of the spinal cord and so what this creates then are um two regions the center of the spinal cord is cell bodies the edges of the spinal cord are axons now what is different about these two regions is that cell bodies um are going to be stained by waterbased stains so when we were studying uh histology when we're studying tissues the cells that we were studying uh were were generally stained using water-based you know hydrophilic tissue tissue stains okay and so the um the cell bodies are going to get stained when we apply a water-based stain to them but the axons we said were covered with uh myelin which was very fatty full of lipids and lipids remember are hydrophobic they repel water so when we apply a water-based stain uh these Remain unstained the stain does not stick to them because it's a watery stain and these are full of lipids so returning to our image of the spinal cord cord what we see here is that the um the gray matter is the part that the part that gets stained and the white matter is the part that does not get stained okay so what's important to understand here is that it's not that the gray matter is gray and the white matter is white because right when we look at this that the white matter is not white um if I go and uh Google um you know images of spinal cord uh cross-sections um you know we're not going to see gray and white um like slides like you see this one right here you would not call this white you would not call this gray um it's it's not intended to be saying that the color is gray and the color is white okay what we're saying is that where the cell bodies are located that gets stained darker than where the um axons are located okay so that's the meaning behind these two terms gray matter is the cell bodies of the neurons whereas white matter is the mile ated axons so when we look at the arrange the the way that the neurons are arranged in the spinal cord the cell bodies are on the inside the axons are on the outside any questions about gray and white matter and that will actually be the opposite for the brain the cell bodies are actually located on the outer surface of the brain so the gray matter of the brain is actually on the outside and then all the axons travel up to that point so the inner portion of the brain is the white matter uh but for our purposes we're just covering gray and white matter with the spinal cord so gray matter on the inside of the spinal cord white matter on the outside so the next thing we're going to do is look at um the nerves that come out of the spinal cord um um so nerves we see here are cordlike organs they're composed of by the neurons and connective tissue that holds them together so that's why we consider these to be organs because they're a combination of nervous tissue and connective tissue the consistency of a nerve is like um lightly cooked spaghetti okay so it's flexible but it's not um but it's a little bit firm so like if you imagine taking linguini lightly cooking it so it's not quite ready to eat and then like if you pushed on it you'd feel like kind of Squish under your finger but still hold its form it's still firm okay and nerves are going to be made from uh bundling neurons that are going to travel in two different directions we said that the first direction is sensory or aeren meaning that the nerve is travel toward the spinal cord and brain carrying information to the spinal cord and brain and motor was the direction going from the brain and spinal cord to the body so we said that was eer going to the body telling the body what to do so in this slide what we point out here is that most nerves in the body are both sensory and motor okay so most nerves in the body the the way that they are arranged is like this where we would have um in in one structure so this here is the nerve in one structure you're G to have neurons that are going in two different directions so you have neurons that the cell body is there and the axons are going this way so let's call these ones uh sensory and then um other um neurons that are bundled up in this same structure are running the other direction so these ones would be motor so in a single nerve you're going to have it carrying sensory information to the spinal cord and brain and then carrying motor information back to uh the body so most nerves are going to be like this but not but not all of them some nerves are entirely sensory and some nerves are entirely motor so some are purely sensory some are purely motor take for example cranial nerve 2 was what carried your sense of vision right that is only Vision so that is only sensory information going to the brain it does not carry motor information back to the eye so cranial nerve 2 does not have any motor function okay um and then we said um facial nerve was the the nerve for facial expression uh so closing your eyes puffing out like puckering up your lips that would be something that is strictly motor and does not have any sensory function so some nerves are are purely sensory and purely motor but most of the nerves and the nerves that we're going to learn about um specifically in this class um are going to have a combination of both sensory and motor function so to create nerves uh the first thing that we need to do is have branches come out of the spinal cord and the branches that come out of the spinal cord are what are called spinal nerves so here is the spinal cord and then we see the nerves that come out of the spinal cord these are the spinal nerves so going back to1 how many cervical vertebrae do we have how many vertebrae do we have in our neck cervical vertebrae get some answers here right keep them coming seven right so we had seven cervical vertebrae how many thoracic vertebrae okay right so 12 and then how many lumbar right so Okay cool so it went 7125 right so 7125 well here we go we look at the um nerves and what we see that stands out immediately eight cervical 12 thoracic 5 lumbar okay uh so this is annoying okay and it's not my fault I did not do this this is just how they name these uh nerves what we see here is that the first nerve that comes out comes out above C1 they call that nerve C1 the next one that comes out above C2 they call C2 the one that comes out above C7 they call C7 the one that comes out above T1 they call C8 okay again I would not have done this if I was naming these I would have been consistent I would have named this T1 we would have come all the way down and you know at the very end would be you know the very last one is named for the vertebrae it comes out above but for some reason they decided that okay we're going to name this one that comes out above T1 C8 and this throws off the whole sequence then because the rule for naming the nerve uh is that in the neck in the cervical region the nerve is name for the vertebrae that it is above so this is above C1 it's C1 this is above C5 it's C5 but then in the thoracic lumbar sacral regions it is named for the vertebrae it comes out below so T1 comes out below T1 T12 comes out below T12 L5 comes out below L5 so that's explained for you here C1 through C7 leave a o the vertebra their same number C8 leaves below C7 every spinal nerve after C8 comes out under the vertebra of the same number with the example T6 comes out under vertebra T6 okay it sucks again I would not have done it this way instead of having one coxal I would have had two coxal nerves and you know eliminated C8 but uh but by emphasizing the thing that it m mes this whole thing up hopefully this makes it easier for you to learn it so just remember that C8 throws it off so everything in the cervical region is above the vertebra of its same number and everything after the cervical region comes out below the vertebra of its same number okay so we have 31 pairs of spinal nerves and then the next thing that will happen is that the spinal nerves are going to crisscross and connect with each other in structures called plexuses so a nerve plexus so looking at the nerve plexuses here we see in the cervical region we see The crisscrossing Happening Here in the um shoulder region this is called the braal plexus we see The criss-crossing Happening Here in the lumbar and sacral regions uh so we see that there are five regions where a plexus forms where we do this crisscrossing and after the crisscrossing what we're going to form are called the peripheral nerves okay and so I'm going to show you guys how a plexus ends up creating uh our uh peripheral nerves from our spinal nerves okay so here is the spinal cord and coming out of the spinal cord we are going to have the branches okay green okay so here are the branches coming out to the the left side here uh so these are the uh spinal nerves okay this spinal nerve that we see right here is going to be um C5 then the next one is going to be uh C6 and the next one is going to be C7 all right so here's the cord running down the the vertebral column here and here are the nerves as they exit from the spinal cord so what's gonna happen is that these uh spinal nerves um are going to Branch okay so we're g to have a fork that forms here with this C5 okay so C5 branches we're going to see C6 Branch okay so C6 is going to Branch just like C 5 did I'm going to have C6 Branch three times okay and then we're going to see uh C7 is going to Branch as well oops I think I did that wrong yeah I did that wrong man there we go okay so um so what we're seeing so far is um the branching that's occurring uh coming out of the um spinal nerves that were branches coming out of the spinal cord and so what we've done here is with all this crisscrossing we have created um a first of all a plexus so this area here is the nerve plexus this area of crisscrossing and what we form at the end of the nerve plexus are the peripheral nerves okay what we see with this first peripheral nerve is it's a combination of C5 and C6 coming together so this peripheral nerve here is c56 this peripheral nerve is a combination of C5 C6 and C7 so this one is C5 through 7 this one is a combination of C6 and C7 okay so what we do here is uh by doing this plexus uh we end up uh creating peripheral nerves um that uh enter and exit from the spinal cord at different levels okay so it's not so simple as to say like the nerve that goes to your bicep goes into your spinal cord at C5 it's more like the nerve that goes to your bicep goes into the spinal cord at level C5 and C6 because it's a combination of both of those channels here okay so that's shown for you in you in your uh notes here they're just not quite mapped out the same way that I showed you to to follow along with the the color coding but what we see here is like C5 and C6 they're coming together to form this nerve this nerve right here is the peripheral nerve called muscular cutaneus um we see C6 C7 C8 coming together to form this nerve you know this nerve right here is uh the uh radial nerve um so um it's the same concept that we have the spinal nerves coming out of the spinal cord and we have the plexus that forms and after the plexus what we've created is the peripheral nerves and we see that the peripheral nerves are the nerves then that run through the body and uh carry information about sensation and motor function um through the body okay so the peripheral nerves after the uh nerves have rearranged in the plexus we form the peripheral nerves these travel through the body carrying information to and from the body uh we have a peripheral nerve handout that will'll go over in the lab and just summarizing what we've learned so far we're going to put this together uh as a sequence okay so um so what we've learned is that this is how sensory information is going to work okay we're going to have a sensory organ that is going to deliver information into a sensory nerve okay the sensory nerve this is the peripheral nerve so what I'll do is I'll sensory peripheral uh nerve is going to send uh its information through the nerve plexis on its way into the spinal cord which will carry that information to the brain okay so this is how sensory information is going to reach your brain um I poke your hand as I poke your hand I squish a sensory organ that we'll learn later is going to be called a pinan COR pusle you know I I activate this sensory organ that stimulates the sensory nerve um that's the peripheral nerve that travels up your arm to the nerve plexus at your shoulder enters the spinal cord W and travels to the brain and you get the information that your hand has been poked okay but we can do the same sequence in Reverse when it comes to motor information the brain is going to tell the body to do something by sending information through the spinal cord through the spinal nerves that are going to form the uh nerve plexus and then coming out of the nerve plexus uh we're going to have our um motor peripheral nerves and the motor peripheral nerve is going to tell the body what to do uh so let's just say um skeletal muscle will be the Target so telling the the body what to do how does this work the brain sends its information through the spinal cord through the spinal nerves that came out of the uh intervertebral foram uh through the nerve plaxis forming the motor uh peripheral nerve that ultimately stimulates the skeletal muscle like we learned in uh the topic on muscle contraction that it's all started with a nerve telling the muscle to contract okay so this summarizes everything we've learned so far as far as a putting it all in sequence so understanding that um these are not individual things like we're not just like heyy there's nerve plexus and nerve plexus does something and then there's a peripheral nerve and a peripheral nerve does something you want to understand that the these are all a sequence brain spinal cord spinal nerves plexus peripheral nerves this is a sequence uh that we're following to get from brain to body and from body to brain okay so any questions about those features the peripheral nerves nerve plexus spinal nerves spinal cord and brain okay so our next topic here um brings up an an interesting phenomenon when it comes to how our sensory information from the body is um distributed through the spinal nerves into the spinal cord uh we form a pattern that's called uh dermatomes and so dermatomes relate to what we saw here how the nerves enter the spinal cord uh when it comes to sensory information the nerves are entering the spinal cord through these um spinal nerves and a dermatome is a region of skin so Derm Dermatology skin the region of skin uh that uh whose sensory information enters the spinal cord through a particular spinal nerve uh so what we see here is that let's take uh the upper body here we see that the skin its sensory information is uh divided up like we see where the thumb coming up the lateral uh forearm and arm the sensory information for all of this skin enters the spinal cord through the C6 nerve route so all of that area comes up and enters right here then we see uh the uh index and middle finger uh we have those they they're going to enter through C7 uh the uh ring finger and pinky finger and a medial arm are going to enter through C8 and so we have these Stripes that form as we look at uh where that sensory information enters the uh spinal cord which of these nerves which of these spinal nerves it travels through what's interesting about this is this is uh used clinically uh to determine whether or not a person has uh an injury to these spinal nerves okay and a person will draw out their dermatome and you just need to remember what this picture looked like a person will say to you oh it's crazy my thumb and just up the outside my arm this whole area just feels numb well a person who's not very good at their Anatomy uh is going to go oh your thumb is numb that's carpal tunnel syndrome forgetting that what we learned about with carpal tunnel syndrome is the thumb and the next two and a half digits on the anterior surface are the things that go numb with carpotonal syndrome when a person says their entire thumb is numb front and back and it's only their thumb you got to remember dermatomes you got to remember that means that the problem is not here at the wrist with carpotonal syndrome that means the problem is right here at the C6 spinal nerve so the person probably has either uh arthritic changes or a disc injury like a disc herniation that's pinching right here and the same thing for the lower body we have the same kind of Stripes but we see these Stripes run from lateral to medial can't tell you how many times I've had a patient draw this for me where they go oh it's the craziest thing it's like I feel like numbness and tingling on the outside of this leg then it crosses over my knee goes to the inside of you know of the lower leg and they're like it's so weird how it goes like that and I'm like actually it's not weird at all it's textbook your problem is right here at The L4 nerve rout this is where your injury is and that's why your L4 dermatome is the pattern of that numbness and tangling okay so what you want to get out of the dermatomes is just get a good understanding this visual remember that the upper body the arm is divided up into you know the thumb the next two fingers the next two fingers in these like striped patterns going up the arm and that the lower body has this stripe pattern you know running across the thigh eventually down the leg across the knee um and that throughout the rest of the body it follows this stripe pattern just running uh Medi to lateral so um you know you're not responsible for knowing the numbering system I'm not going to ask you specific questions about you know where is the C6 dermatome but just get this sense of you know this pattern and un and understand that that pattern uh is a dermatome a dermatome is an area of skin uh whose sensory information goes through a single spinal nerve route a fin point about this unfortunately it's not a perfect system there is some uh overlap over dermatomes so one person their C6 dermatome um you know might look just like this and the next person their C6 dermatome might you know Branch over to the next finger a little bit or something along those lines so you know let's say coming over here you know that somebody's uh L4 might be higher up into the L3 area it's not a perfect system but it at least G gives you the pattern that Clues you into where the problem might be um and in microbiology we'll learn about how dermatomes relate to uh shingles which is another neat pattern that that we follow um so uh with that uh got to throw another another nervous system joke your way um now that we've gotten through the anatomy there so the last thing we have to do is learn about uh the last of the three roles of the spinal cord and that was reflexes um so spinal cord we said was responsible for um controlling reflexes a reflex is a quick involuntary stereotyped reaction what we mean by this stereotyped it's the same every time so I hit you in the patellar tendon with a reflex Hammer your leg is going to kick forward you're going to extend the knee if I hit you with that reflex Hammer a hundred times in the same spot you are going to extend the knee every time that's what we mean by stereotype it's not going to change it's not gonna be like sometimes I kick out and sometimes I kick to the side no every single time it's going to be the same reaction so our somatic reflexes um are contractions of skeletal muscle that result in the withdrawal away from a harmful stimulus and things like the knee-jerk response that we uh saw um uh that we see in in a clinical setting and how a reflex works is the following it begins with a somatic receptor so a a receptor in the muscular skeletal body or skin that senses danger okay you've put your hand on a hot surface you have been hit in the tendon with a reflex Hammer this is dangerous hitting a tendon with a reflex Hammer uh remember what we learned about with dense regular connective tissue this is strong in this direction it is weak in this direction so hitting you in this direction poses a risk to this tendon there's a chance that if this force is any stronger you're going to tear that by coming at it like this so that sudden Force against the fibers of the tendon is sensed as danger and that information about the danger is carried through AER sensory nerve fibers to the spinal cord so you are at risk sensory information goes to the spinal cord telling the spinal cord your patellar tendon is at risk or your hand is on a hot surface the spinal cord is the integrating Center the spinal cord is what makes the decision about what to do your hand is on a hot surface your patellar tendon has been struck what do we do pull your hand away or kick that leg out to take the tension off of that tendon the decision is made in the spinal CT the decision was made and the message is sent through motor or eference nerves to the skeletal muscle telling the skeletal muscle what to do relax the quadricep I'm sorry contract the quadriceps relax the hamstring and in that way you'll be able to kick the leg out take the tension off of that tendon and prevent it from tearing pull your hand away from the hot surface so the eference message tells the skeletal muscle what to do the skeletal muscle carries out the response and that is the action of the reflex okay what you want to understand about this reflex and the role of the spinal cord notice that this whole thing happened without the brain okay so think about this think about how special a reflex is okay think about how fast this occurred I put my hand on a hot surface you guys have all done this before you've all experienced this reflex where you touch a hot surface and how does it go you touch it you pull your hand away and then you go ow right it's it's not ow and pull your hand way it's pull it away then go oh my God that hurts what happened there is you touch the hot surface the message went to the spinal cord spinal cord said get your hand off you got your hand off while that message was also going up to the brain the message went up to the brain said your hand is burning and it hurts but you've already taken your hand away okay so you even you haven't even sensed it yet you haven't even gotten the the pain in the hand before your hand is pulled away okay think about how slow that would have been if you had to think about it if you touch that surface and it had to go all the way to the brain and you go man my hand is really hot like way hotter than I want it to be oh it must be because it's on that surface I should take my hand off of that surface and then you take your hand off by that point your hand is is cooked right you're going what smells so good in here who's cooking right you that is not safe that is not a way to preserve the body so reflexes are uh triggered by the spinal cord so we don't have to involve the brain so we can do this so much faster you're taking a step and the ground is uneven your foot hits that uneven ground and you get that sense that the ankle is rolling that message goes to spinal cord the spinal cord fires back and says well if you keep rolling you're going to strain your ankle so you need to do something you need to pull that foot off so that you don't strain your ankle just because the ground's a little bit crooked okay so we rely on reflexes to prevent injury because the spinal cord can make a decision so much faster than the brain ever would and that allows for us to do those immediate respon that's hot get your hand off of it that uh you know that uh tendon is being overstretched do something to prevent it from being stretched to the point of tearing so protect the body as fast as you possibly can that is the role of the uh somatic reflex and it is all possible because the spinal cord makes the decision instead of the brain any question questions about somatic reflexes and how they work