hello students today we're going to talk about the spinal cord anatomy and physiology in chapter thirteen of our book in this chapter we're gonna learn how to describe and identify certain anatomical features of the spinal cord discuss some of the functions of the spinal cord as it relates to homeostasis in the body and spinal reflexes and what a reflex arc is so the spinal cord is involved in processing reflexes that are initiated in order to maintain all of our controlled conditions at stable levels within physiological ranges the spinal cord integrates the epsps and ipsps which we covered in chapter 12 excitatory postsynaptic potentials and inhibitory postsynaptic potentials so all of that's integrated within the spinal cord and then the spinal cord conducts both sensory nerve impulses up to the brain and motor impulses out to the effectors of the body the spinal cord is protected in three primary ways as you know this panel cord travels down the vertebral column you cover the vertebrae and the axial skeleton and lab so it runs down the vertebral foramen in the middle of the spinal column so the bone protects it there are connective tissue coverings that wrap around the spinal cord as well as the brain and those three primary connective tissue wrappings are called the meninges you may have heard of meningitis before that's infection inflammatory responses to those connective tissue membranes and then cerebrospinal fluid which is the life fluid for the brain and spinal cord basically transports oxygen and nutrients and waste products to and from the the neurons that for the spinal cord and we're gonna look at where that cerebrospinal fluid flows in a minute the three connective tissue layers that protect the spinal cord and also wrap around the brain and include the dura mater which is a very tough dense fibrous connective tissue layer you see right here where it's identified I'm not gonna put these pictures on the test but we need to know where the layers are so the dura mater is outermost layer that surrounds the entire spinal cord just inside of the dura mater is what we call the subdural space so there's a little space in here between the dura mater and then this layer right here which is called the arachnoid mater just deep to the arachnoid mater is where as we'll learn in a minute routes connect spinal nerves to the spinal cord there's also a space in here is called a subarachnoid space this is where cerebrospinal fluid flows around the outside of this pannel cord and then we have denticulate ligaments which anchor the spinal cord in place within the meninges just deep to this subarachnoid layer surrounding the outside of the spinal cord directly is this little bitty layer right here that's called the pia mater so those are the three layers from more superficial to deep you have the dura mater on the outside the subdural space the arachnoid mater the sub are racked in the weight space where a cerebrospinal fluid flows around outside of the spinal cord and then you have the Pia mater which adheres to the outside of the spinal cord directly again that's called the Pia mater now as far as the spinal cord is concerned with its anatomical features the spinal cord starts just after the medulla oblongata and as it's exiting the foramen magnum out of this all the spinal cord then extends all the way down to the level of l2 if you remember your lumbar vertebra so we had five lumbar vertebrae so the spinal cord pretty much terminates at l2 but then we have some extensions that come from the spinal cord that form what we call the lumbar plexus and the sacral plexus ease that we'll look at in a minute and all of those roots coming down from there are is called the cauda equina now there are two major enlargements of the spinal cord there's what we call a cervical enlargement you can kind of see right here how the spinal cord is a little thinner and then it enlarges right here that's called the cervical enlargement and then it gets kind of thin again until we get down here which is called the lumbar enlargement now there are 31 sorry there are 30 one pair of spinal nerves so the spinal nerves have attachments to the spinal cord which we're going to look at in a minute and then they have branches that come off of end that are called the RAM eye so we're gonna look at some of these Ram eye and look at what their names are in a minute but all of the anterior roots of a spinal nerve form a plexus somewhere except through the thoracic region at least down here and into here so we have a cervical plexus we're gonna look at a brachial plexus there's a lumbar plexus and the sacral plexus notice there's not a thoracic plexus only cervical brachial lumbar and sacral as far as the internal anatomy of the spinal cord is concerned you're going to be learning how to identify the parts of a spinal cord and lab we haven't done that yet but nonetheless let's look at what's in here first of all down the length of the spinal cord are pairs of spinal nerves there's 31 pair of them they branch off at each level of the spinal column that you learned about with the vertebra so we have seven cervical vertebrae you have 12 thoracic you have five lumbar five fused sacral and then you have the the Cox Adiel area so there are actually eight pair of cervical nerves because the first pair of cervical nerves come off just before c1 so all spinal nerves have two attachments to a spinal cord so this is a spinal nerve right here so this little branch right here is called the anterior root of a spinal nerve and then back here is what we call the posterior root of a spinal nerve and notice in how the neurons enter and leave via a spinal nerve to come to and from the spinal cord as it turns out all sensory neurons carrying sensory information from the periphery of the body enter via the posterior root of a spinal nerve and all of those sensory neurons for those that are entering the posterior root have their cell body in this enlargement right here which is called the posterior root ganglion so the axon then extends through the posterior root into the posterior part of the spinal cord this is posterior over here this is anterior over here and that sensory neuron has several fates that as far as synapses are concerned they only show you no one here but the sensory neuron comes in the posterior root and that's where they will synapse with either inter neurons in this case they show an inter neuron or they can synapse directly with a motor neuron the motor neurons in this picture is the red and this this little green colored one but nonetheless we always have sensory information coming in the back posterior part of the spinal cord and we have motor information leaving the anterior root from the anterior part of the spinal cord through the anterior root to enter the spinal nerve and those nerve impulses then are conducted to all the effectors in the body like skeletal muscle cardiac muscle glands so forth and so on so the internal structure of the spinal cord is also separated into white matter areas that's the areas on this picture that look alike that looked lighter and gray matter areas which is a little bit darker and that's not really grey in the picture here it looks more Brown but the white matter areas are called columns so we have posterior white columns this these on this side are the posterior white columns then we have lateral white columns on either side of the spinal cord and then we have anterior white columns right here the gray matter is separated into horns so we have a posterior grey horn at these regions we have lateral grey horns along the edges and we have anterior grey horns towards the anterior side of the spinal cord now notice these motor neurons we're going to talk about this a little bit more in chapter 15 but the cell bodies of these motor neurons are in a particular place the motor neurons that lead the spinal cord via the anterior root of a spinal nerve the motor neurons that are associated with the autonomic nervous system will have their neuron cell bodies embedded in the lateral grey horn whereas the motor neurons for the somatic nervous system that is to say that motor neurons that that innervate and activate skeletal muscle contraction always have their neuron cell body and the anterior Guri horn just like this picture shows us here so we're going to revisit this concept once we get into chapter 15 so we have gray horns we have white matter tracts which are all in what we call the columns the white matter areas contain neurons that carry information up to the brain up this panel from the brain back down the spinal cord the gray matter areas actually conduct information into and then out of this panel cord so what's not shown in the picture are some neurons that actually extend their axons do anyway extend up and down the spinal cord through the white matter tracts we won't be learning all of those names but I call I like to call the white matter area the superhighway the spinal cord information flows up and down the spinal cord very quickly in the white matter tract Arya's and information that comes in and out through the gray matter is what I like to call the on/off ramps from a highway so you can exit and re-enter in this fashion so sensory information always comes in the posterior route motor information always leaves via the anterior route so I hope that kind of makes sense a little bit all right now the spinal nerves have the job of connecting all of our sensory receptors and all of our effectors in our body like muscles skeletal muscle cardiac muscle in the glands to the central nervous system so in which case all of the spinal nerves which carry neurons to it from the central nervous system are part of what we call the peripheral nervous system this was introduced in chapter 12 so there are 31 pair of spinal nerves that are attached to the spinal cord via anterior and posterior routes as I just showed you make sure you review these animations I'm sure you've been doing that so keep that up so it'll help you out a little bit now let's look at the connective tissue wrappings that cover a spinal nerve directly so spinal nerves are actually collections of many many many neurons axons of neurons in the body and they're all wrapped up in connective tissue so you have no nerves in your brain and you have no nerves in your spinal cord because there is no connective tissue in the middle of your brain or the middle of the spinal cord and a nerve is classified as connective tissue wrappings of many many many neurons in one structure so this would constitute the nerve with all of the axons and neurons being wrapped up in connective tissue around it so let's look at the connective tissues that surround a spinal nerve surrounding the outside of the spinal nerve directly along the outside is what we call the epineurium that's the outermost connective tissue wrapping of the spinal nerve on the inside of a spinal nerve axons from neurons are actually organized into these circular structures which are called fascicles each fascicle is separated from all of the other fossa khals within a single nerve via connective tissue referred to as the peri nerium so peri nerium basically organizes groups of axons in one circular structure called a fossa chol on the inside of a fossil each axon of each neuron is actually separated from all of the other ones also via a connective tissue layer called the endo nerium so the endo Nerium wraps around the axons of individual neurons being transported through the nerve that are organized within us the same classical so3 connective tissue wrappings the epineurium the perineum and in donor ium organizing the axons of neurons in a nerve again a nerve is a collection of many neuron axons of neurons in one place that are organized and wrapped together via three connective tissue layers so for that reason there's no nerves in your brain because there's no connective tissue in your brain we do have a bunch of neurons in the brain a whole bunch of them same thing in the spinal cord but they're not wrapped up in connective tissue so we don't call them nerves in the brain a whole bunch of axons in the brain and spinal cord all referred to as a tract not a nerve so we'll get to that later on as well all right so let's look at how we have the attachments of the nerves in the spinal cord and you can see here this is a thoracic vertebra by vertebra and we're looking at the superior section like down the length of the vertebral column you can see the spinal cord in cross-section here but there's a whole bunch of these weird little branches everywhere so let me tell you what all of these are so first of all a spinal nerve is where we have an attachment on the posterior section here that would be the posterior root and an anterior attachment from the anterior root where the posterior root and the anterior root join together is called the spinal nerve now there's branches from that spinal nerve these are called the roots the posterior and anterior roots but when we have a branch it's called a ramus so there's an a posterior ramus that goes to the back musculature so there's a branch that comes from that spinal nerve it's called the posterior ramus we also have an anterior or ventral ramus that would come out and wrap around to go to the anterior part of our body basically around to your your thoracic cage and to your abdomen so forth and whatnot we then have these special branches that will come off of a spinal nerve they actually will be introduced more so in Chapter 15 these branches are called the Rhema communities they cause four neurons that are associated with the autonomic nervous system to enter and then leave something called the sympathetic ganglion on the sympathetic trunk so again we're going to cover this in chapter 15 in more detail but these are the main branches we have a posterior ramus and anterior ramus often called the dorsal and ventral ramus so let's talk about the server the plexus ease down the length of the spinal cord so we have a plexus that's formed from that and the plexus is always formed from the anterior lami of the spinal nerves so I want you to know a little bit about what I put on these slides in fact the information that you need to know for this test is going to come from this PowerPoint so make sure you review all the slides so the cervical plexus comes off around the cervical region specifically between c1 and c5 so notice we're gonna have letters and numbers the letters represent the level of the spinal cord really the vertebral column where we are so C stands for cervical and then the nerves are numbered so the cervical plexus includes the anterior Ram I of cervical nerve number one through cervical nerve number five so that's how we're going to name the nerves down the spinal cord the cervical plexus nerves which I'm not making you learn all of them but I do want you to know this one the phrenic nerve the phrenic nerve is a branch from the cervical plexus and it carries neurons to your diaphragm and causes your diaphragm to contract which allows you to breathe so basically the phrenic nerve is involved in allowing the respiratory system to work the way it does for you to breathe in and out but nonetheless in general the nerves from the cervical plexus you can see them all in bull-type don't go and learn all of those but the nerves from the cervical plexus pretty much supplies the skin and all the muscles in your head and your neck region and the upper parts are superior portions of your shoulders your chest and then the diaphragm specifically buying the phrenic nerve the brachial plexus is formed from the spinal nerve c5 through c8 so the rest of the cervical nerve and then the first thoracic nerve so from t2 down to t12 is where we don't have a plexus so the brachial plexus provides most of the inputs for all of the muscles and structures in your shoulders in your and your arms your upper limbs we have a few main nerves that are of some importance we have what's called the median nerve it actually has a couple of little heads to it lateral and a medial head not gonna worry about those but we have a median nerve we have a radial nerve in this ulnar nerve you have other nerves that come off but these three extend down our arm so let's talk about them a little bit and what the other major nerves are so we have an axillary branch that's going to go to the structures of musculature around your armpit the muscular taneous nerve and the three that I just mentioned the radial median and ulnar nerve so I want you to know that these are some main nerves that come off the brachial plexus and also with the brachial plexus in particular the median nerve and ulnar nerve when we have problems with it so if we have injuries to our brachial plexus one problem is what we call an herb Duchene palsy or what we call a waiter's tip so in this picture you can see that the individual has a flexed wrist and really the fingers would also be would be flexed they just don't show it all that well but the wrist is flexed and they lose sensation down the lateral medial to lateral part of the arm and have the inability to extend the wrist and fingers so they can't make their wrist straighten back up in other words that's called the herb duchesne palsy now the lumbar plexus is formed by the anterior Ram I of L 1 2 L 4 so lumbar nerves number 1 - lumbar nerve number 4 and these nerves help supply the anterior and lateral portions of your abdominal cavity your wall and the external genitalia and the lower parts of our body which includes our legs our lower limbs so all of the anterior lateral part of your abdominal wall the external genitalia and your legs are supplied by some of these nerves I listed two important ones the femoral nerves and obturator nerves so just know those although we have these other branches that come off just know what I wrote in this picture the sacral plexus is formed from l4 l5 and sacral 1 through 4 so I want to know which nerve supply each plexus that's why I wrote this at the top of each one of those slides so the sacral plexus supplies the muscles and in the buttocks and the structures in the perineum the perineum is the bottom part the groin area in the middle the medial aspect of it's called the perineum and then also have branches that go to your lower legs one thing of importance here for the sacral plexus is the largest of the nerves that go down are leis which is called a sciatic nerve gives rise from the sacral plexus and you can see here if you look close in the picture they show that common fibular and the tibial branches so ultimately these would branch down or leg and I'm sure you've heard of sciatica before inflammatory response to the sciatic nerve kind of painful so the sciatic nerve is coming from the sacral plexus not the lumbar plexus now what about the physiology of the spinal cord I kind of hinted on this earlier the spinal cord is involved in maintaining homeostasis by integrating in sensory information and motor information and propagating impulses where they need to go so we're not learning all of the tracks in a spinal cord but again I want you to know the white matter tracks conduct nerve impulses to and from the brain up and down the spinal cord whereas the great mater receives and integrates incoming and outgoing or what I should say sensory information and motor information respectively that are involved in initiating and performing spinal reflexes so we need to talk about what reflexes are and what a reflex arc is so reflexes are fast typically fast involuntary unplanned responses to particular stimulation that means for instance if you go to swallow something and you start coughing you say I swallowed something down the wrong pipe well when you have foreign objects fluid food starts to hit the tip of the opening of your windpipe it causes for a very forceful reflex that causes coughing to expel it from your windpipe so if you step on a tack you lift your foot up real quick you stick your finger in boiling water you pull your hand out real quick so those are involuntary reflexes that are initiated at the spinal cord level and or some of those in the brainstem but in this case we're going to talk about the spinal reflexes so the gray matter of the spinal cord is going to basically serve that integration Center to control the spinal reflexes that will occur and I want you to review you know the animation for reflexes that's definitely going to help you out and let me show you what a reflex arc is now this is also a linkable a clickable link up here you have to be connected to the Internet to see that like the other ones but nonetheless as far as a reflex art is concerned a reflex arc is the pathway with which information takes to allow the reflex to occur for instance this is our picture of a reflex art they start with number one and go all the way to this number five so I'll just follow it in the skin a nail or attack you know goes in the skin which is going to hurt we have sensory receptors in our skin pain receptors and other receptors that fire sensory impulses up the spinal nerve that enter the spinal cord via the posterior root of the spinal nerve and there depending on the type of receptor and sensory neuron and reflex that will be initiated different types of synapses will occur so this is just in general the sensory neuron comes in and may synapse with what we call the inter neuron inter neurons if you remember from chapter 12 are totally confined within the central nervous system that inter neuron then synapses with a motor neuron in this case that motor neuron it has this neuron cell body an anterior grey horn which means this motor neuron will leave ultimately always via the anterior root of a spinal nerve and innervate skeletal muscle so always would know what the effectors going to be for this particular type of reflex because of where this neuron cell body is located so reflexes that are occurring in the spinal cord depending on what type of effector is either activated or inhibited is called something different for instance in the case of reflexes that initiate skeletal muscle contraction the reflex would be referred to as a somatic nervous system reflex because the effector is skeletal muscle in Chapter 15 we're going to look at autonomic nervous system reflexes and because they control the effectors in the body we don't have conscious control over and we're actually going to break them down into specific types of autonomic reflexes so I'm going to cover that in chapter 15 so this is what we would call a somatic nervous system reflex and we're going to learn some terms this is what we would call a polysynaptic hypsi lateral reflex so let me tell you what those are polysynaptic means that the reflex involves multiple synapses so here's one synapse between a sensory neuron and an Internet on and another synapse between the inter neuron and the motor neuron so we have multiple synapses so that means we would have to call that a polysynaptic now if we have the reflex having sensory information coming in one side of the spinal cord and the motor information leaves from the same side of the spinal cord that's called hypsi lateral so this is an ipsilateral poly synaptic reflex arc and so you see the terms here if see lateral means that sensory and motor information enter and leave on the same side of the spinal cord contralateral is when the sensory information comes in one side of the spinal cord but the motor information leaves from the opposite side of the spinal cord and we also have to either call it monosynaptic or polysynaptic depending on if we have one synapse that initiates the reflex or multiple synapses that initiate the reflex in the case of somatic nervous system reflexes we also have something called reciprocal innervation typical innervation or inhibition is a situation where we need one muscle group to contract to bring about the movement of a body part which means we need the opposite or antagonistic muscle group to be inhibited so let's look at what this entails what you're looking at right here is something called a stretch receptor reflex some people often call this the patellar reflex or knee-jerk reflex if you hit the patellar tendon with a reflex hammer it stretches the tendon this is the insertion of the the Quadra suit quadricep group muscle tendon is going to insert right here on the tibial tuberosity of the tibia and if you hit that with the reflex hammer it stretches the tendon in wording so by doing that we have what's called a stretch receptor reflex when the tendon is overly stretched to alleviate the stretch of the tendon we cause the muscle group to contract so if you contract your quadricep muscle group it's gonna make you extend your leg at the knee and that's why they show this arrow with a leg coming up this would be the outcome of the reflex with your leg kicking upward or extending at the knee so by contracting the Quadra Squad recep group muscle you can then pull on the tendon which would alleviate the stretching that we initiated with the reflex hammer now reciprocal inhibition or innervation involves the in hip inhibition of the antagonistic muscle group in this case it would be the hamstring group muscles which include the semitendinosus semimembranosus and the biceps femoris so all three of those muscle groups that are on the back of your thigh which are learning hopefully you're going to learn in lab when you identify them when they contract it causes you to flex your leg at the knee so the contraction of that muscle group the hamstring group would cause the leg back in this direction contraction of your quadricep group muscles which include includes the vastus medialis rectus femoris vastus lateralis and vastus intermedius those four muscles are called the quadricep muscle group and when they contract it causes an extension of the leg at the knee so let's see how this reflex works first of all we have sensory receptors in the muscle and in and around our tendons by the way so we have this sensory receptor in our muscle called a muscle spindle and it will fire along the sensory neuron carrying sensory information into the spinal cord at the posterior root of the spinal nerve and you can see we have several different fates so first of all that the stretch reset stretch receptor reflex is a mono synaptic hypsi lateral reflex because of this branch right here you see how the sensory neuron even though we have multiple branches from the same neuron this primary branch comes down and synapses with a motor neuron directly that leaves via the anterior root of the spinal nerve to go and cause your quadricep group muscles to contract this is going to release acetylcholine on the muscles and cause it to contract which would cause an extension of your leg at the knee and thus alleviate the stretch of the tendon so this is a protection reflex to prevent over stretching of tendons so we have the sensory information coming in and a motor information leaving directly however in order to get an extension of the leg at the knee we have to inhibit the hamstring group muscles or what we call the antagonistic muscle group we don't want them contracting because the leg is going to try and come back the other way so at the same time we have what's called reciprocal inhibition and if you notice the sensory neuron has another branch the reciprocal end innovation or inhibition is called a polysynaptic if SI lateral reflux because we have two synapses multiple synapses and the information the motor information leaves on the same side of the body that the sensory information came in so it's still epsy lateral so the reciprocal inhibition is a polysynaptic hypsi lateral reflex now this other branch that comes up right here goes to the brain basically making your brain aware of the fact that the reflex occurred in other words you're going to know if your leg extends outward you're going to be able to feel it because we feel everything in the brain so we have a branch that goes up to the brain in our white matter tracts and the white columns of the spinal cord all right so just review the steps involved in this reflex which is really two different reflexes that occur at the same time a monosynaptic EPSA lateral reflex to cause the Quadra suit quadricep group muscles to contract and a polysynaptic hypsi lateral reflex that causes inhibition of our antagonistic muscle group which in this case would be the hamstring now the last reflex that we're going to look at is a tendon reflex and the tendon reflex is a reflex that prevents a muscle from putting too much tension on a tendon so it prevents the tendon from ripping or tearing so let me just read clarify that let's go back one this patellar tendon reflex which is a stretch receptor reflex when you strip hit the patellar tendon with the reflex hammer is going to stretch the tendon which pulls on the muscle and the muscle becomes stretched so to alleviate that muscle stretch we need to contract it and that's what this monosynaptic if SI lateral reflex does it causes the quadricep muscle to contract which then shortens it and prevents it prevents it from being over stretched and the tendon reflex this is a reflex that's going to prevent a muscle from contracting and thus putting too much tension on the tendon to prevent it from ripping or tearing so this particular reflex involves really two things as well we have what's called a tendon organ the tendon organ is a receptor in and around the muscles and Attendance that monitor the degree of tension on the tendon so if the quadricep group muscle is contracting it's going to want to bring your leg forward because when your quadricep muscles contract it extends your leg at the knee so if you are lifting a heavy weight load and you're trying to lift your leg up if the weight load is too much and we're putting too much tension on the tendon ultimately your muscle will be forced to relax with this inhibitory reflex the sensory information goes up the sensory neuron and we have a polysynaptic if SI lateral reflex that goes to the skeletal muscle and inhibits it so the motor neuron is actually inhibited from releasing acetylcholine on to your muscle and thus prevents it from contracting and it makes it relax and all of that happens because of these inter neurons notice what you see a plus sign or a minus sign the plus sign means that there is an excitatory postsynaptic potential or an excitatory neurotransmitter being released and where we have a minus sign is an inhibitory postsynaptic potential so in this case this inter neuron here releases an inhibitory neurotransmitter which inhibits the motor neuron supplying the quadricep group muscle from firing so when this motor neuron does not fire the quadricep group relaxes and your leg is going to stop going for now to alleviate the tension even more that were being that's being forced on to the quadricep tendon we can also contract the antagonistic muscle group which in this case is the hamstring group which includes the semimembranosus semitendinosus and the biceps femoris so we had that sensory information coming in saying hey there's too much tension being placed on the on the quadricep tendon and we have to inhibit the quadriceps from contracting but we want to initiate or stimulate the contraction of the antagonistic muscle group so in this case the sensory neuron has an excitatory neurotransmitter released the inter neuron also releases an excitatory neurotransmitter and initiate this motor neuron going to the hamstring group muscles to fire causing them to contract and our leg is flexed at the knee as our leg moves in this direction so that's going to stretch our muscle back out and prevent more tension from being placed on the tendon when our leg moves back in this direction so make sure you just go and review the steps involved in this reflex art this is the pathway that the information takes and the outcome of the reflex again if you ever have any questions please email me and I will answer them for you okay so before we end the video all the way I just wanted to go over a couple of these terms with you just go and look up these terms I'm sure you've heard of paraplegics and quadriplegics so I want you to know what these are certain spinal cord injuries it can cause a loss of use of limbs around the body mono Pelageya or mono/poly Jake is when an individual loses ability to control one of the limbs paraplegic or paraplegics have limbs on either the arms or the legs on both sides of the body they can't use it so a purse and I can't use our legs or paraplegic hemiplegia half of the body parts are inhibited from being used on one side of the body and then a quadriplegic is an individual who loses the loses the ability to control all four limbs so just go and look up these terms I might have a question or two on that but that's about it all right so if you have any questions just email me and I will answer them for you