hey everybody welcome to chapter 13 so we've introduced ourselves to basic nervous tissues now we're going to take a look at a couple of things here one is the spinal cord so our first look at in lecture here at the central nervous system of brain and spinal cord or the CNS we're gonna look at spinal nerves a little bit although you'll do most of your learning there in lab and then in the spinal cord itself we're going to take a look at the a sending and descending spinal cord tracts the a sending tracts of the sensory tracts the descending tracts of the motor tracts so there's a number of those and you know there's some learning that goes on there and then we'll also take a look at spinal reflexes those reflex arcs that occur in the spinal cord which is a part of the central nervous system processing that takes place outside of the brain so here we're gonna start with some imagery that you should know from lab really so that we're doubling up a little bit here with lab you know here's our basic look at the spinal cord we know starting at the foramen magnum of the skull passing down we have the cervical enlargement here in the lower cervical and upper thoracic vertebrae and that accommodates the increased neural traffic through the brachial plexus in and out of the arms we pass inferior to that we go through the thoracic region and we get to the lumbar enlargement which is where our lumbar plexus nerves pass out into the leg and we have increased neural traffic in and our little legs and so that we needed a large portion of the spinal cord for that very abruptly inferior to the lumbar enlargement we have the conus medullaris where the spinal cord comes to an end so the the medullary cone there the physical spinal cord there stops growing before you reach the age of ten but your body keeps growing and so as you continue to grow your skeleton the spinal cord stays right there ends up being right around l1 to l2 and then the spinal nerves that come out inferior to that have to stretch way down way down and this bundling of the spinal nerves which are l3 through s5 and the coccygeal nerve all have to travel through the vertebral canal together we call this the cauda equina because it looks like a horse's tail and that's when in latin cauda equina means horse's tail now before I went any further talking about like whole spinal cord structures I wanted to come to this diagram first or set of diagrams really to talk about the the meningeal layers it's important and the positioning of the spinal cord in the vertebral foramen which we can see on the top of this first of all well let's let's come down here and and see some stuff that you know we we talked about in lab you know so we have the the meningeal layer right the three meninges these are connective tissue coverings of the central nervous system they have various functions the innermost layers the Pia mater here mater means mother in Latin see these are the mother layers across the nervous you know central nervous tissue so the Pia mater is like a shrink wrap right on the surface of the spinal cord and brain the arachnoid mater here is is quite different you can see here it's superficial to the pia and so as between the Pia mater and the dura and here's the dura mater out here the tough mother are the dural sheath here so this this arachnoid mater here is responsible for containing and circulating the cerebrospinal fluid so how do we do this if you look up here what we notice is that between these meningeal layers there are spaces or potential spaces so for example between the Pia mater I'll zoom this up even really much closer than that so if we if we look in here here's the the Pia mater on the surface and here's the arachnoid mater so between the Pia mater and arachnoid mater we have this subarachnoid space and you can see that labeled way over here subarachnoid space that subarachnoid space is where the cerebral spinal fluid is circulating now we will talk extensively about cerebral spinal fluid is production and circulation in the next chapter okay but I wanted to introduce the concept here so we could talk about a you know a few a few aspects here of spinal cord anatomy if we look here there is the dura mater in orangish red whatever that color is right there's actually a space between the dura mater and the arachnoid mater it's called the subdural space it's a potential space only there's no actual gap there but it's it's anatomically defined outside the dura though you see here they show adipose tissue in the epidural space epi means above or outside so there's no subdural space in all practical sense but there is an epidural space and that lies between the dura mater and the bone of the vertebra of the vertebral canal so these are you know this image here shows us some interesting things first of all these spaces here and the primary space we pay attention to is this subarachnoid space all this shaded blue here and that's where our cerebrospinal fluid is the epidural space out here with its fat now this fat has zero physiological significance to the spinal cord here but it has a lot to do with cushioning of the spinal cord in the vertebral canal listen your central nervous tissues don't do well when you bruise them so we have many many things in place to make sure that you don't do that one of those is that we have in the spinal cord in the vertebral canal we surround the spinal cord with adipose tissue so it's cushioned on all sides we also if I back off here when we talk about protection of the spinal cord the dura mater here a is a very tough connective tissue layer but what you notice is that the arachnoid mater and dura mater follow the nerve roots away from the spinal cord and out into the nerves in fact the dura mater here becomes the outer connective tissue covering the epineurium of the nerves so remember this diagram here we just came from if we consider each of these spinal nerves that come off at every level followed out by the dura and arachnoid that anchors like like a bunch of buttons all the way up and down like a zipper locking the spinal cord into place because it's completely enveloped by that dura mater that then gets locked into place at every spinal nerve it's kind of cool actually so that's another aspect of spinal cord stabilization another one here is these denticulate ligaments I'll use a different color here these denticulate ligaments here and what we these didn't ticular ligaments occur at every spinal level also and I'll show you a better picture of these in a cadaver section on the next slide they also stabilize the spinal cord laterally left or right okay and then at the termination of the spinal cord will come back up to this upper right diagram here in a minute that determination of the spinal cord at the conus medullaris hey the arachnoid and dura mater layers keep going in the line the vertebral canal all the way down to the base of the sacrum but the pia mater doesn't the Pia mater ends at the conus medullaris with one small exception so we'll come back in here and remember what we were looking at here so here's that cauda equina and the medullary cone the conus medullaris let's come back up to that conus medullaris so here's the the end the termination of the spinal cord the point you have here the dura mater and arachnoid mater keep going so that subarachnoid space is that blue space with a strip of spinal fluid circulating it keeps going so the spinal nerves of the cauda equina are completely bathed inside this chamber and that's actually called the lumbar cistern but the Pia mater the Pia mater off the tip of the medullary cone keeps going as the filum terminale and when it reaches the very end here of where the dura and arachnoid mater stop it continues on where it gathers with it also the dura and the arachnoid and they travel together all the way down to the X and that becomes the Coxes you ligament down here so the the Pia mater really that connective tissue is what makes that filum terminale inside the cauda equina region and as it passes out of that cistern area it gathers with it the dura and arachnoid and they travel together as one band of connective tissue and that provides stabilization vertically for the spinal cord so that filum terminale is pulling down and stabilizing spinal cord vertically where the spinal nerves and the denticulate ligaments are stabilizing it laterally and it's being cushioned by adipose tissue all up and down so the spinal cord is well taken care of inside its vertebral canal there here is here's a look at some cadaver sections of human spinal cords and I show you this to kind of give you a little bit better idea of the the root layout and the meningeal layers so let me zoom in over here for a second what are we looking at here here's the actual spinal cord right and there's your anterior media Fisher so we're looking at this from the anterior or ventral side and what do we have here is a ventral root right because we're looking at it from the ventral side and so the ventral roots the anterior roots are facing us and you can see and this one right here you can see the dorsal root going away from you in the screen that's kind of cool but I want to look at the meningeal layers if this is the actual bare surface of the spinal cord this is the Pia mater so that lighter gray tissue and it's right on the surface and whoever did this dissection has resected it off a little bit and then here this gap right here is your sub arachnoid space because this tissue right here is the arachnoid mater and they have it labeled right there so here's your arachnoid mater here's your subarachnoid space and this tissue layer out here is the dura mater they've pulled that way aside so it's over here too and you can see the nerve roots passing through the dura and the dura is going to follow those out into the spinal nerve you can see how the nerve roots have kind of punctured that and gone out through so yeah I just I wanted to show you this and then they've got the denticulate ligaments here so you'll see there's one here there's one here there's one there there's one there there's one there there's another one there do that so at every between actually every spinal level there's a denticulate ligament stabilizing a spinal cord from side to side and it's enveloped in those three meningeal layers and so here's a different look and actually if if you notice here we have the posterior median sulcus and now we have a posterior view this is the posterior root there's the anterior underneath there there's the ganglion on that posterior route so we're just seeing it for another way so here's the dura mater here they have the arachnoid mater I don't know if they actually have the Pia mater on this but yeah I mean it's spinal cord is pretty neat so I just wanted to show you a few things about this stuff so that we can have some intelligent discussions later and in lab this should be familiar territory to everybody a look at the spinal cord itself we have this idea of gray matter and white matter the gray matter being on the interior of the spinal cord the white matter being under on the outside the gray matter being the horns we call them and the white matter being the columns and we're gonna see later in this chapter we call them columns because information is going up to the brain and back down from the brain through this white matter so this is vertical information whereas gray matter is horizontal information in the spinal cord like virtually everywhere else in the body we have bilateral symmetry so we have left side right side we have to be able to determine anterior from posterior though once you can do that you're in good shape the best and easiest way is to look at the roots out here all right so look here we have the dorsal root and the ventral root okay so ventral dorsal how do you know the dorsal the dorsal has this ganglion here so the dorsal root ganglion there's a bulge and the dorsal root not in the ventral keep in mind here that the dorsal root represents incoming sensory information the ventral root is outgoing motor so these are one-way ventral out dorsal in once they reach the spinal nerve then they become two-way traffic within the same nerve and you can kind of see a little bit better that up here so once you know dorsal here there's some other ways to do it first of all on the ventral or anterior side there's a fissure here called the anterior median fissure on the dorsal side it's not a fissure they're not separated it's what's called a sulcus and a sulcus is there's a couple of sulci here they only label the median one that's where two pieces of tissue come together they are separate tissues but they are physically bound together so it just makes a crease here that separates from left and right so that's a sulcus that's a fissure okay so on the ventral side you have a root with no ganglion and you have the fissure dorsal side you have a root with the ganglion and just a sulcus you once you get used to looking two things you can look at the gray matter here and you can pretty much tell the dorsal or posterior gray hornet be sharper and point here and the ventral gray horn will be wider and rounder sometimes there's a lateral gray horn we will wait until we do the autonomic nervous system chapter to talk about that because that's that's an important aspect there with the columns here you know if you're from the root from the ventral root to the fissure we call that the anterior column or ventral column between the roots it's the lateral column and between the dorsal root and the sulcus is the posterior or dorsal column if we come over here this is stuff for lab but you know you can see the same thing on a tissue slide here's a look at the gross anatomy of a nerve this will look very familiar to anybody who knows about the gross anatomy of whole muscle you have a connect tissue layer on the outside that's very tough this is the epineurium and that's going to be contiguous with the dura mater so when the dura mater follows the roots out it becomes the epineurium and then you have fascicle bundles inside carrying axons myelinated or unmyelinated but they're carrying axons inside the fascicles and so the fascicles tend to bundle together axons that are going to and from the same region it's just like any kind of wiring setup you might have and then inside the fascicle which is surrounded by a paranormal layer you have the axons that are then cushioned in an aerial art issue and that's called the end of maryam so this can be very similar to muscle layout this this set of diagrams this an interesting look at kind of the the intersection here of the two spinal roots the dorsal and ventral root and the spinal nerve I'm going to key in here on the top portion first alright so remember with the ventral root here that's outgoing motor traffic so those are signals from the central nervous system going out to the skeletal muscles and such and the dorsal root years bringing sensory information in right and that comes in to the dorsal gray horn okay so the spinal nerve itself is two-way traffic right outgoing and incoming but the the to a traffic splits at the root so they become one way out going into ventral and going in incoming on the dorsal the reason that we have a dorsal root ganglion here is because the sensory neurons u44 your sense of touch which is what these are is that somatic sensory you know you don't have vision coming in on these you don't have hearing you don't have to smell you don't have taste right what's coming in and the spinal nerves is your sense of touch and some what we call somatic sensory neurons so I want to remind us here of the structure of these neurons and these are unipolar neurons so we went over that in Chapter 12 all right so sensory the touch sensory neurons are unipolar and so when we take a look at that these cell bodies have to be somewhere remember the cell bodies on the unipolar neuron are off of the axon that are not in line with the axon like a bipolar neuron the cell blight is off to the side so all of the sensory neurons come up here again if you have a sensory neuron coming in on this spinal nerve so it comes in this way and enters you know that like that its cell body is here in the dorsal root ganglion so that's that bulge is for all of the sensory neurons coming in at this particular spinal root they're all in here that's with all these little little jelly beans are in here you can see the little stalks coming off of the axon and going into that cell body yeah so there's a there's one right here saying so here comes this particular sensory neuron and there is its soma right there so that's what the dorsal root ganglion is it's a collection of all of the sensory neuron cell bodies for that particular side of that particular spinal level all right and then out here in the spinal nerve you got the motor out in a century and all together because it's just axons hey that's just axons the the axons for the motor neurons their cell bodies are in that ventral gray horn we talked about that in lab now this diagram here is meant to help us build on some of the things that we saw in lab some of the vocabulary that I asked you to learn for example I mean so we've been doing you know ventral root and dorsal root in the dorsal root ganglion notice here they have anterior and posterior as a vocabulary we've talked about this in lab the posterior dorsal the same thing anterior and ventral is the same thing he kind of got to get used to having those used interchangeably okay but another thing we had you learn was for example the sympathetic chain and we had you learned that as those roots dorsal ventral come out from the spinal cord they merge into a spinal nerve and we had to learn several branches off of that for example we had to learn the posterior ramus of the spinal nerve and we had to learn the anterior ramus of the spinal nerve and then we had you learn the communicating rami the gray and white communicating ram i they go from the spinal nerve over to the sympathetic chain and we said every time that a gray and white ramus communicate from the spinal nerve to the pathetic chain they they connect at a ganglion so there is a bulge there just like the dorsal root ganglion the sympathetic chain ganglion is a collection of cell bodies of nerves and again we'll talk about that in the autonomic chapter so we had to learn those things that you might not have had the best context okay again we'll we'll talk sympathetic chain and autonomic nervous system in another chapter but for example if you talk about the dorsal and ventral Ramos Ramos and LAN just means branch the anterior or ventral branch versus the dorsal or posterior branch look over here this larger picture it's actually neat because it shows you the spinal cord in the vertebral canal okay and then here's the roots coming out and they've got one set expose where you can see inside another one you can just see that the outer Eponine covering um but what do you got as it emerges you have the communicating Ram I coming over to the sympathetic chain they're not showing much of the chain here because they're just showing one level but that chain there is coming at you through the screen and going away from you into the screen and then what do we got we have and I'll I'll trace this we have a anterior or ventral ramus and it's called that because it's the branch that comes around the front of the body I'm back off of this a little bit here see it comes around the front of the body so that's the anterior or ventral rimas the posterior or dorsal ramus goes out I can do it better there we go goes out the dorsal aspect and goes around the back so you'll notice on all the models the anterior ramus is much larger than the posterior or dorsal ramus because there's a lot more tissue here and a lot more nerve so if you go posterior to the spinal cord ain't much back there don't need a very big nerve set there what you need mostly is anterior ramus so that image there I hope gives you a little more context visual you know recognition for the types of things that you were looking at on those lab models alright so enough of that stuff because you know what everything we've talked about then this lead-up half-hour here is stuff that you've covered in lab already for the most part a little bit of value added here and there now we're talking about some new things here so here's where we're going to take a look at the the vertical aspect of the spinal cord and its physiology and the white matter columns so what do we have here on the left we have the a sending tracts outlined in red so these are sensory so if they are ascending they're coming in from the body through the dorsal root ganglia and into the door so gray horns and they are bringing sensory information in and that sensory information is going to then be shared upwards to the brain and it's going to travel upward on one of these a sending tracts and so they've outlined the white matter column regions and red here that are carrying this a sending sensory information they've labeled them so we'll take a look at the posterior column pathway the spinocerebellar tracks and the anterolateral system so the spinothalamic tract is one we will mostly consider and then over on the right we have the descending tracts so these are motor so when the brain makes a decision about movements than these motor commands go down the spinal cord and out the muscles following one of these pathways they're highlighted in green here please don't get confused I've had people confused by this and they think that the a sending information is going up one side of the spinal cord and descending is coming down the other side no no if I if I pull out my my green marker here and if we consider for example the lateral corticospinal tract for example okay so the lateral corticospinal tract is in this region of the lateral column that's why it's called lateral this the lateral corticospinal tract is also present right over here on the same and the same position mirror image on the other side of the spinal cord okay so everything you see here has a left and a right version here okay so we're going to take a look at these you know one one set at a time we're gonna do sensory first and then we're gonna do motor and I'm going to illustrate for you some basic vocabulary that we use in the spinal cord and central nervous system to follow these tracks and we'll do a little bit a little bit learning here so let's take a look okay we're gonna start here with the spinal thalamic pathway keep in mind these pathways are often named for their starting and ending point spinal thalamic starts in the spine and goes to the thalamus part of the brain we're going to learn about so the spinal thalamic pathway now when we do these things first of all so we're starting with sensory these are sensory pathways these are a sending pathways so we'll keep this tract sensory a sending okay we want to know what information does it carry and we want to know where does it D cos 8 you don't know what that means yet I'm gonna explain it all right so let's talk about vocabulary here when looking at spinal tracts I I'm gonna look up here there's a key here look at this notice here we have red white and black so we're gonna follow the arrows and notice what we have here is first-order second-order and third-order neuron so what we have here is when we take a look at sensory information we can have up to three neurons in sequence synapsing with each other the first order is your sensory neuron can be a second order and can be a third order so we're going to pay attention on these maps where the first-order second-order and third-order is and we're going to keep track of where it D cos eights now what de cos eight means where does it cross over from one side to the other well no sorry erase out there we go where does it cross over from one side to the other and then the third thing here we're going to keep track of is how does it a send again I gotta fix my spelling here hold on ace and the spinal cord so let's take a look at these two pathways and I guess there's there's two portions to the spinal alignment pathway there is an anterior tract and a lateral tract so you see the anterior over here you see the lateral over here the anterior spinal amick tract here this is this side anterior spinal thalamic tract it says carry crude touch and pressure sensation that's highlighted down here crude touch and pressure sensations so this diagram is showing it coming in from the right side all right look what we got here remember red was the first order neuron so you think first order is the first neuron in in order that's carrying information so what do we have here this little red neuron right here that's the sensory neuron so on these a sending pathways the first order neuron is always the sensory neuron it's the one that's actually entering the spinal cord okay and then look what happens there's a synapse here this is how they are going to communicate with you on these diagrams let me show you something they are always going to have a situation where they're going to show some around soma you know a long axon and an arrow and then they're gonna do around so long son and an arrow and then around soma a long axon in an area the idea this is a neural circuit neural wiring diagram this is how they're showing you synapses and communication between neurons so there are synapses so what do we got going on here the first order neuron is going to synapse with a second order neuron and on these diagrams the white is the second order neuron and look what happens here so we said one of the things we wanted to know is I'll even put this back out where does it take us eight where does it cross over from one side to the other that's that term dicus eight it looks to me like on the anterior spinal thalamic tract the second order neuron dica Sates immediately so you dicus eight at the same level as you enter the spinal cord and look it Dickus ates through the anterior gray commissure right there and once it dicus Eights then it enters a white column and goes north goes up towards the brain and that's the anterior spinal the lam ik tract because it's in the anterior white columns there's your anterior median fissure this is the anterior white column this is the anterior spinal ammok tract so our first order neuron enters the gray horn a dorsal gray horn immediately synapses with a second order neuron which immediately Dukas Eights enters the anterior tract and goes up through the spinal cord so over here says how does it a send the spinal cord in this case the a sentience through the spinal cord is on the opposite side of where it entered so the term for this is contralateral so I'm going to put this vocabulary down here I'll come over here for a second okay if the information a sends on the opposite side of the spinal cord from where it entered this is called contralateral a sentient I'm not exactly sure if that's how you spell essentially looks right so this is contralateral ascension if this over here let me give myself a little more room so if information a sends on the same side of a spinal cord from where entered we call this epsilon rule ascension contralateral and EPSA lateral these are your vocabulary terms for the information heading up and down the spinal cord so in the case of the anterior spinal thalamic tract we have the first order neuron enters immediately synapse of the second order which immediately crosses over or dica Sates and then at a sends contralaterally now keep in mind right here medulla oblongata and midbrain by the time you reach this slice here you're in the brain so this is the spinal cord this is the spinal cord here we're in the brain brain brain so let's follow this second order neuron today sends contralaterally enters the brain at the medulla so now we're inside the you know a foramen magnum or in the brainstem pass up through the brainstem and we hit this blue thing here and let me zoom in on this blue thing here this blue thing is the thalamus that's the blue thing and so here we synapse with another neuron this is our third order neuron the third in the pathway so in the thalamus we synapse with a third order neuron and that third order neuron goes to the cerebral cortex the gray matter on the surface of the brain that's going to interpret that information please don't make any try to make any sense of this homunculus idea we're gonna talk about this in another chapter try not to put too much effort into that yet so here's one of the two tracks in the spinothalamic pathways so the anterior carry crew touch and pressure sensations now there's also you know anterior spinal lamech information coming from the other side so it'd be mirror image on this left side here you would synapse in the dorsal gray horn and the second worker neuron or dicus eight and a send contralaterally and the other side of the spinal cord so the the two sides would be mirror images they're only showing one side on these diagrams to simplify them over here we have the lateral spinothalamic tract okay let's follow this we have a first order neuron enters the spinal cord in the dorsal root immediately synapses with a second order neuron that second order neuron immediately because eats and enters the lateral spinothalamic tract now because it's not in the anterior column it's in the lateral white column may send contralaterally to the brain passes the brainstem to the thalamus synapses with a third order neuron and projects to the cerebral cortex so what's going on here the lateral spinothalamic tract carries pain and the thermal sensory information temperature pain temperature on the lateral crude touch and pressure on the anterior these are called the spinal flank pathways they project directly to the thalamus and then the thalamus relays that to this cerebral cortex so vocabu-larry vocabu-larry vocabu-larry sorry about that my screens not cooperating with me okay here we go we want to know what information does it carry right there you got that where does it D cos 8 we got that how does it a send contralaterally we got that I want you to be able to follow these maps and I want you to keep track of this stuff well let's look at this one this map is the posterior column pathway posterior column pathway it's called that because these tracks here make up the entire posterior white column so all of the white matter of the posterior white column is this pathway right and it's pure sensory a sending information well what do we got here we've got what is it carrying fine touch vibration pressure and proprioception okay and again this particular diagram is showing from the right side of the body you will see a mirror image of the left side okay but we'll just follow it from the right side so fine touch vibration pressure and proprioception you might say what the heck is proprioception okay this is these are joints and muscles have sensory receptors in them and what this does is it gives your three-dimensional position of your body the idea is if you close your eyes and you reach your arm out and then keep your eyes closed pull your arm in turn your hand over turn it back squeeze your fingers let your fingers out do things with your eyes closed and your brain knows exactly where your arm is in three dimensions because it actually has a dedicated set of sensory receptors in every knuckle in your wrist in your elbow and your shoulder and all the muscles that run all those there are sensory receptors there that are dedicated to telling the brain exactly what angle every joint is and what position every muscles in it tells your brain what your body's position is in three dimensions that's proprioception it's pretty cool stuff so this is coming in on the posterior column pathway so that's what we're being carried so let's follow the the neurons the first order neuron comes into the dorsal root and into the dorsal gray horn it does not synapse it immediately enters the posterior white column and a sends the spinal cord to the brain so what happens is is that sensory neuron enters the spinal cord it doesn't synapse it keeps going all the way up to the brain so I want you to think about this if you have a proprioceptors for example in your big toe so we just said hey your brain knows your position of your big toe at all times because it has proprioceptive in those joints that sensory neuron that's entering your spinal cord from your big toe is going all the way up the spinal cord to the brain before it synapses so that sensory neuron goes from your big toe to your brain that's one soma and one axon as basically as almost as long as you are tall that's a lot neuron so in the posterior column pathway the sensory first order neuron does not synapse immediately it immediately a sends EPSA laterally on the same side it enters the brain here's the medulla oblongata in the medulla it synapses with a second order neuron then the second order neuron dicus Eights enters a new tract inside the brain called the medial lemniscus labeled there and goes to the thalamus we've seen that before synapses with a third order neuron projects to the sensory cortex the cerebral cortex so what are some things to know here I want to pay attention to a few things here first of all we have some vocabulary here we have the nucleus gracilis and nuke askew nyada's here in the brain we have the fasciculus gracilis and fasciculus CUNY artists here in the spinal cord so when we we talk about fine touch vibration pressure and proprioception that's actually a lot of information that's a really a lot of information alright so it has to be organized well when we look at these posterior columns here each one of them is actually split into two bundles each bundles of fascicle there's one fascicle that's the grow silly fascicle fasciculus gracilis and then there's one fascicles that's the CUNY eight fascicle for the fasciculus CUNY artists they're just Latin names don't worry about the Latin names right just but there's two bundles within this column and different in for me or the the information being carried on those bundles is coming from different sources so I want to outline this for you so the vasila fasciculus gracilis here if this is carrying information all right so it says all of this stuff this this fine touch vibration pressure proprioception but the fasciculus gracilis is carrying info the information from t7 and below so ill thoracic vertebra number seven if this fine touch and the vibration pressure and proprioception is coming from the spinal nerve t7 or below all that information is going to be on the fasciculus gracilis if it's coming from t6 or above it's going to be carried on the fasciculus cuny on ttis so we don't we split it by upper body lower body Hey and so basically t6 and above is going to be you know your thoracic cavity arms and above and t7 and below is gonna be the abdominal pelvic cavity and legs okay so they're both carrying fine touch vibration pressure and proprioception but it's by position of where it's coming in at which one of these you're going up right one's the gracilis ones the cuny eight then each one of these projects to a slightly different region in the medulla oblongata in the medulla oblongata you have two centers called nuclei the nucleus gracilis that's where the fasciculus gracilis is going to go to a nucleus Kenyatta's that's where the fasciculus great keaney artist is going to go to once you reach that nucleus then you synapse with your second-order neuron which immediately crosses over and then keeps going north you know up through the brainstem on a new track called the medial lemniscus and like lemniscus in latin means ribbon it's the medial ribbon because it has that kind of flat shape of a ribbon but you know don't read too much into it there's just called by what they look like but the information then goes up through the brainstem and again there's that thalamus so the ventral nuclei and the thalamus and then the third order neuron projects to the cerebral cortex so this is the posterior column pathway carrying a certain kind of information here the a sends the spinal cord EPSA laterally dica Sates in the medulla oblongata and then terminates in the cerebral cortex after synapsing in the thalamus so there's another one of these pathways all right so here's our our last sensory pathway that we'll look at the spinocerebellar pathway now this diagram you'll see leaves a lot to be desired but I'll use it because it has the same kind of visual conventions and I can illustrate a few things for you but we're gonna draw our own set of diagrams to illustrate these pathways first of all what's the spine of cerebellar pathway so it's going from the spinal cord to the cerebellum so let's look over here the cerebellum here we haven't talked brains yet here but the cerebellum this is a motor control center your cerebellum which is Latin for small cerebrum is basically a subcontractor for your brain who's dedicated to the sole purpose of refining motor movements making your motor movements better more coordinated more highly controlled so if you learn to play the flute you're really working your cerebellum to figure out your fingerings on the flute and all of the little things that go into that so the cerebellum to motor control center now for motor control let's take a look here what is the spinal cerebellar pathway carrying here get the whole thing in what's the spinocerebellar pathway carrying is carrying proprioception proprioception now we just talked about this on the previous slide your body knows your position of all your joints and all your muscles great so the posterior column pathway sends that information up to the spinal cord through the spinal cord to the medulla oblongata to the you know nucleus CUNY artists and the nucleus gracilis and then it goes up to the medial lemniscus to the thalamus and the thalamus to the cerebral cortex okay that posterior column pathway is how your cerebrum learns or knows about the position of your body but if the cerebellum is going to be able to do its job it needs to have its own proprioception information input so the cerebellum has its own set of proprioceptive input so it doesn't have to go asking the cerebrum hey what position is your big toe in it knows directly because it has its own pathway for it that's what the spinocerebellar pathway is so there's one difference from what we've seen before what we've seen before is all this sensory information has gone to the thalamus and then gone up to the cerebral cortex here is going to the cerebellum second since we're not going to the cerebral cortex we're not going to the thalamus there's no third order neuron here there are only first order in second order and the spinocerebellar pathway so two neurons instead of three the other thing is every other pathway we've looked at the other three really four you know two spinal thalamic tracts and then to posterior column pathways all of them you start on one side where the information comes in and you eventually somewhere you dicus eight and that information ends up on the other side so the central nervous system or you know the virtual e all of the information that gets handled by the central nervous system the right side of the brain is processing information from the left side of the body because everything decays it goes over to the other side so the right side of your brain is handling the left side of your body the left side of your brain is handling the right side of the body that's how your central nervous system works by and large except in the spinocerebellar pathway in the spinocerebellar pathway the cerebellum is handling information from the same side of the body so that's where these diet this diagram here leaves a lot to be desired we're going to do this better because if we try to read this diagram it's only going to confuse you so we're gonna do a custom diagram here so let's go over here to the side kind of keep that a little bit over there okay so I'm going to draw the spinal cord and draw nice and thick here so here's my spinal cord yeah in case you were wondering this is the cerebellum you all right so there's the spinal cord and there's the cerebellum all right we are going to draw our spinocerebellar pathway here let me get a red pen here to represent our first order neuron coming in from the left side of the screen okay so here we are we're inside the spinal cord right so we've got first order neuron here so with the spinocerebellar pathway we synapse now with a second order neuron and if you look at that the diagram you'll notice that there are two different tracks in the spinocerebellar pathway there's an anterior tract and a posterior tract now if we are on the anterior or I'm sorry the posterior tract or we will synapse immediately on the same side in the dorsal gray horn and the second order neuron is going to a send EPSA laterally up to the cerebellum and it's going to directly enter the cerebellum so this is the posterior spinocerebellar pathway I'm going to zoom in here I'm going to label this thing so here's the posterior spinocerebellar it's a posterior so look the cerebellum here is handling this information from the same side of the brain there's been no crossing over there's no decussation and we everything's being handled EPSA laterally ascension as ipsilateral and processing is Epsilon okay well what about that other one there the other tract the anterior tract here comes another first order neuron set and we are going to synapse now me I'll use green for this one so we synapse immediately in the dorsal gray horn and this time the second order neuron dica Sates immediately at the spinal level and it's going to a send now contralaterally and so here I'm going to zoom in again and label this thing like I did before so this is the anterior cerebellar tracked so one one dicus eights and a sends hips contralaterally one doesn't because a and a sends hips laterally but here's the kicker this is where the game gets exciting this anterior spinal cerebellar it Ditka Sates again in the brain and ends up on the same side that it entered so the cerebellum it's weird its handling you know proprioceptive input from the same side where it entered so the left cerebellar hemisphere is receiving proprioception from the left side one of the pathways stays on that side of the spinal cord er the one goes across goes up and then comes back it's the weirdest thing but you know I don't get to make the rules I just teach them right it's going to be the same thing from the other side so we can show for example let me say here we come in from the other side I could show a posterior coming in here like that and then I could have my other one coming in here d you know synapse there d cos eighths goes up the other side of the spinal cord and then comes back and that's what the spinal cerebellar pathways look like they're all carrying proprioception it's just this is the only example in the entire central nervous system where you have double decussation it's just that's the only place you see it it's kind of abstract but there it is so don't please don't try to read this diagram okay sister gonna confuse you as far as understanding the tracts and the posterior versus anterior just use this custom diagram here and you're probably even better off just using one half of it I mean I added in the right side of the diagram just for illustration purposes but you might wanted to stick to the first half that we did so there's the first half I guess of the chapter so what did we do we we kind of reviewed spinal cord anatomy and nerve and Adam II and things like that which basically doubled up from lab and then we started in on these spinal cord tracts and pathways so we talked about all the sensory a sending pathways the major ones so that's where I'm going to end it here on this this particular lecture recording so when we come back for part two of chapter 13 will do the descending pathways the motor pathways how does the brain send motor commands down the spinal cord as that will occupy our time for a little bit and then we're going to take a look at spinal cord reflexes so mono and poly synaptic reflexes of the spinal cord so that's going to be this second part so I'll see you then