Okay so we've talked about the brain and when we talked about the brain we talked about the cerebrum we talked about the diyon we talked about the brain stem and we talked a little bit about the cerebellum those are all parts of the brain and then we're going to talk about the spinal cord and those all represent neurons in the central nervous system so we have a skull and we have vertebrae and the brain is sitting inside that skull and the brain stem leaves that skull and when it leaves the skull it becomes the spinal cord okay so that's what we've been spending time talking about that stuff in the green is our central nervous system so our our spinal cord is going to also have gray matter and white matter remember we said the cerebral hemisphere was pretty much all white matter centrally with a bunch of gray matter pushed up against the outsides the last the outside two to maybe four millimeters or so is all gray matter when we look at the spinal cord we're also going to see gray and white matter and the gray matter is neurons and that applies to the to the cerebral hemisphere as well neurons and unmyelinated fibers and the white miter is myelinated fibers and you know I mean nerve fibers when I say fibers right everybody's good with that so generally the spinal cord is generally arranged as Central gray matter so you can see up here with what we drew here the gray matter was out in the outside edges and the white matter was Central so and the peripheral is what matter so just the opposite of what we saw up in the brain I'm going to show you a picture of this in a minute and also generally dorsal which is interchangeable with posterior is typically going to be sensory and ventral interchangeable with anterior is most often going to be motor in its responsibilities so spinal nerves for so spinal nerves are going to come and go from the spinal cord if they enter the spinal cord on the back side then they match up with what we said they're going to be sensory when they exit through the ventral route at the front they're going to be motor okay so what that's going to look like is if we look at the spinal cord so let's uh just draw the bottom of the skull here okay and the spinal cord is going to leave whoops I don't want that color it leaves the there's a big hole in the base of the skull it's called The Fan Magnum big hole and the spinal cord leaves and it travels through the cervical spine remember there were seven of those then it travels through the thoracic vertebrae and it gets a little narrower as it descends and we'll explain why in a minute then it enters into the lumbar spine and it's only in the first two segments or so before it starts to split up into individual nerve fibers and I've kind of spread them out they're not going to spread out like that because they still stay in the lumbar vertebrae but this back end is the end of the spinal Co spinal cord itself and it's literally called the horse's tail the C aquana and that's at the about the level of the second lumbar vertebrae but after between every vertebrae including the skull and C1 there's going to be a pair of nerves now because they're nerves they are not part of the central nervous system they are part of the peripheral nervous system so we'll talk about those and how they match up in a few minutes but let's take a look at this spinal cord so it's a solid mass of nervous tissue until we get to L2 okay and if we looked at a cross-section so if we take out a crosssection okay we're going to look at it now from a crosssection we're taking a slice of the spinal cord and at the back so this will be dorsal I'll label it in a minute uh let's just back that up a little bit try to keep it more or less uh okay that should get us our general organization now that Central little Canal I just drew it's going to have fluid in it anybody remember what that fluid's called CSF spinal fluid that's right both of you are right it's cerebral spinal fluid abbreviated CSF so it's not only going to be found in that Central Canal where provides some nutrition but it's going to be found between the pomatter and the arachnoid matter around the outside of this spinal cord as well so this represents the spinal cord and we're going to whoops I want we're going to have this is anterior and this is posterior okay so we're going to have a root that enters the spinal cord on the posterior side and one that leaves the spinal cord on the anterior side okay okay so in this example what we're going to do now is draw in our gray matter okay that's our gray matter and the out side of the gray would be white matter so we know the white matter are tracks if those tracks are ascending what kind of information is being carried in them sensory right and if they're descending tracks M that's right so most of our ascending tracks will be found in the dorsal and the lateral columns so those columns are just the sides so if we say lateral column then we're talking about laterally dorsal dorsal and anterior would be anterior and if we are able to designate bundles of fibers then typically we're going to find that those bundles that are found laterally uh and Po and posteriorly are ascending now there happens to be laterally descending and anterior ascending so there's a mix there so you don't have to worry about that okay if I name a you're going to be able to figure out whether it's carrying sensor information or motor information for example there's a tract out there that's called the spinothalamic tract if it's called the spinothalamic tract does it sound like it's ascending or descending it should be as correct so what kind of information would be carried in that spinal thalamic tract sensory exactly and if I told you there was a tract that was called the cortical spinal tract cortical spinal tract does that sound like it's descending or ascending descending of course and if it's descending what kind of information is it carrying motor very good how about this one reticulospinal ascending or descending descending exactly if it ends in spinal it's descending if it starts with spinal it's ascending and then you know what kind of information is being carried in it okay so right for now that's all we need to remember okay so let's take those out of there now in the gray matter we said gray matter was neurons and unmyelinated fibers but in this gray matter and I'm going to make this gray matter here a little bigger so we can put some stuff in there so the Great matter is arranged in what kind of looks a little bit like a butterfly sometimes it's described as a bit of a butterfly it looks like it's got wings and you know those big hairy extensions on the back of them that give them these four extensions these four sort of appendages but in the gray matter each of these appendages represents a group of neurons and in what we call the anterior horns these two extensions here are referred to as horns and in the anterior horns we have some of the largest cells in the body we know muscle skeletal muscle cells especially are pretty big but these cells are multipolar somatic motor neurons they're going to leave through the dorsal rout okay and they're going to travel in a spinal nerve so remember we said that spinal nerves will leave the spinal cord through a uh a vental route I might have said dorsal there I meant me anterior is ventral okay so this is the direction if it's leaving the spinal cord then by definition it's eer and we know that eent is motor we good with that yes sir okay now we okay somebody else yeah we're okay okay s sorry just to clarify are we recording yeah can't you tell I I pressed record I can't tell from here sorry well somewhere somewhere on there there's an indicator that it's being recorded no it doesn't tell I can see it it says it's recording okay now this turquoise line I just drew represents the sensory input to the spinal cord so a spinal nerve is going to have both a sensory and a motor component to it so we'll talk about that when we get to the peripheral nerv system but what we need to see is that this sensory neuron is entering the spinal cord but we drew the body outside these are sensory neurons they can either be somatic and you remember if they're somatic sensory they're receiving Sensation from receptors found in the skin they're going to give us temperature and touch and that's that kind of thing from the skin but they could also be visceral Sensory neurons meaning they're going to carry those same sorts of Sensations but from organs and glands inside the body we're okay with that right so this structure is called a dorsal root grion so dorsal cuz it's at the back there's our posterior so we know we're at the back the root is the part of the spinal nerve that's entering the spinal cord but there's a ganglion a cluster of neurons just outside of the spinal cord so part of the peripheral nervous system it's called the dorsal root gangon because of where it's found and inside that dorsal root ganglion are sensory neurons and you can tell hopefully by the way I drew that kind of a mess right now let me now I'm going to draw in a different one as well to indicate this rle as well as somatic okay and they're going to enter through that dorsal route but there's a cluster of the neurons that stay outside of the central nervous system found in this dorsal root gangon and from the way I drew them how would you describe these neurons you got three options they could be multipolar bipolar or unipolar unipolar bipolar they're unipolar there's only one post in and out a bipolar neuron would look like this one two this has a single post single pole unipolar the sensory neurons that contribute to the spinal cord are unipolar okay and we're left with one more group of I got to see if they're going to show up so the sensory neurons enter the anterior rout or sorry they enter the dorsal root and they travel into the dorsal Horn of the gry matter and sometimes they synapse right away on a second neuron and sometimes they travel up in one of the ascending tracks towards the central nervous system towards the brain but these purpley neurons that I just drew in here these are known as autonomic motor neurons so they're going to be neurons that finish on what kind of an affector uh nobody body can answer me and it's right there right in front of you cardiac muscle atos tissue glands and and SK skeletal muscle smooth muscles smooth musle smooth muscle skeletal muscle is voluntary not autonomic skeletal muscle will be considered somatic eector the other affectors all of them once you have skeletal muscles separated all the rest of them fall under autonomic so autonomic motor neurons are going to ultimately finish on glands or smooth muscle or cardiac muscle or adapost tissue that's it everything except skeletal muscle and that is for the somatic motor neurons so this represents the or organization of the spinal cord gray matter in the middle white matter on the outside in a crosssection of the spinal cord we see anterior horns in the anterior horns we see the sematic motor neurons they're sometimes called Alpha motor neurons but basically if you remember somatic motor that's going to tell you that they finish on skeletal muscle the lateral part of these these horns are for autonomic motor neurons you got the word motor in there so you know they're going to finish on an effector if it's autonomic it's everything except skeletal muscle in the dorsal horns we have the fibers from the sensory neurons the neurons themselves are out in the dorsal root ganglion this is the dorsal root this is the ventral root does that make sense yes so sir so you know how you like um describing or telling us all the points like there's the dorsal the lateral which one is for the multipolar sematic motor neurons the vental root is how the neurons the axons from those neurons leave to Target skeletal muscle I colorcoded it for you awesome thank you okay so um vental rout is motor dorsal rout is sensory uh sir uh what does it say under sematic sensory nerves the one that's like underlined in pink visceral oh visceral okay so that means that means like an organ right an organ yeah yeah okay with that yep okay so let's move out that spinal cord then that's what we want to kind of remember about the spinal cord now what we want to talk about is is out in the peripheral nervous system spinal nerves because once we get the spinal nerves figured out we can put those three boxes and arrows all together and have S come up with some examples that hopefully ties everything together for us that's what we're going to try to do before we're finished here tonight so when we look at spinal nerves we're no longer brain or spinal cord so we're part of the peripheral nervous system right that's our pns now we have about 31 pairs of spinal nerves and the spinal nerves are arranged much the same way as the muscle was so in other words on the outside side of a nerve there's a Parry I should say that one the very outside is going to be our epin nuum and better better not mess you up that way and then we notice that there's bundles of nerve fibers that travel separate from other nerve fibers and they are separated by by the perin nuum and then in individual nerve fiber is separated from other nerve fibers by an endon nuum so we can look at a single nerve fiber an axon that might be motor and probably all those ones in a single bundle remember those were called fices when we looked at the muscle tissue right those might all be motor so they're all heading out towards skeletal muscle and then a different bundle is sensory and it's carrying sens information back to the spinal cord so spinal nerves are described as being mixed they have both motor and sensory fibers now if your motor are going to be a that are going to finish on skeletal muscle or autonomic targets like smooth muscle or cardiac muscle if they're sensory they're probably dendrites heading back towards those cell bodies that we saw over here these cell bodies right in here so when they're coming this way they're coming towards a cell body they're dendrites by definition when they leave the cell body they're Aon so we have 31 pairs they leave between the oxop put and C1 and then between C1 and C2 C3 and C4 all the way down into the sacrum and so they're just going to be named for the vertebrae that they're most closely associated with the first one that leaves is C1 and then the next one would be C2 C3 and those are referred to as their nerve Roots so in the cervical vertebrae because we start above C1 there's actually eight cervical nerve Roots C1 through to C8 and then 12 for thoracic that makes sense because there's 12 thoracic vertebrae five lumbar five sacral and on average there's a about one from the coxic so that's how we get our 31 pairs of spinal nerves so that looks like this [Music] um eight cervical 12 thoracic five lumbar whoops um yeah five sacral one atoxic so if we drew a little picture of our vertebrae remember we have a vertebral body and then we have these this vertebral Canal here spinus processes and the transverse processes right remember that was our cross-section of a vertebrae everybody okay with that yeah so in the center of this vertebral Canal is our spinal cord actually you know what I should have I don't know if this will work there's our white matter for our spinal cord and our gray matter remember our gray matter is a butterfly so I'm going to try and draw in our butterfly here so we're at a cross-section we're looking above a vertebrae here and we had our motor neurons would leave anterior so this is anterior that's posterior they're going to leave like this and our sensory neuron came in this way and enters the spinal cord that way let's actually move this over a little closer so our spinal nerve has a motor component to it and a sensory component it splits right before the spinal cord into the anterior roote or the vental root and the dorsal root with the dorsal root ganglion and it's doing the same thing on the other side so we have our sensory neuron bringing sensory into the spinal cord and the motor so that's our spinal nerves we get just the spinal cord we split into a dorsal root and a ventral root ventral is motor dorsal is is sensory so that's our pair of spinal nerves at one level if we looked at the vertebral column coming straight down finishing in that tail at about the level of L2 leaving the skull pair of nerves pair of nerves pair of nerves pair of nerves all the way down 8 12 5 5 1 we get it we okay with that yes okay so these represent the spinal nerves remember we mentioned cranial nerves there's 12 pairs of cranial nerves 31 pairs of spinal nerves so these 31 pairs of spinal nerves have the responsibility of receiving Sensation from all over the body and delivering motor signals all over the body and we we arrange these these roots so they're going to be named for the vertebrae that they're closely associated with so we call a set of nerve Roots C1 nerve Roots they're from the right side c1s from the left side C2 C4 C6 C7 up to C8 and then T12 up to 12 L1 2 3 4 5 S1 2 3 4 5 that's just how we name the nerve Roots When we combine branches from the nerve Roots we get the names of nerves you've heard of the ner nerve or the radial nerve or the femoral nerve maybe you haven't heard of all those nerves but those those are that's where these nerves come from so when we have branches from Individual nerve Roots form nerves they come from what are called a plexus so a a a nerve a spinal nerve so a SP a nerve a spinal nerve plexus is is a network of branches from nerve roots that form specific nerves so there's four main plexuses that we want to be aware of the cervical plexus is made up from the nerves from C1 to about C5 okay there's a little bit of overlap so C4 C5 is where the cervical plexus is so if we had C1 C2 C3 C4 C5 what we're saying is that the nerve roots from C1 and C2 and C3 and C C4 and C5 they all leave and they have branches that will form nerves so they branch and form nerves that will have specific names and responsibilities so you see where the network comes from the network of branches that I'm talking about in the cervical plexus it's C1 through C5 forming branch es with nerves that have specific responsibilities so these nerves are going to supply the chest and the upper back they're going to supply muscles associated with the neck okay and one of the most important nerves that comes out of the cervical plexus is a nerve called the frenic nerve anybody heard of the frenic nerve before no so it's made up from branches from c34 and five and IT Supplies the diaphragm now next semester you'll find out that the diaphragm is a very very important muscle associated with respiration if we cannot contract the diaphragm we are unable to breathe properly becomes life-threatening people who fracture their neck and sever their spinal cord at the level of C4 you can see here right in the middle are in danger of completely damaging the frenic nerve and losing the function of the diaphragm so this is probably the most important nerve from a life-threatening point of view that comes out of this cical plexus you follow me there yes okay so if we were looking at this and we said this is three four and five 3 four and five uh we could come up with contributions from 3 4 five are going to come in on this can I do that right 1 two 3 okay we'll do it like that that's Got Roots we don't need this one in the middle here so this would be our frenic in the the way that we just drew it three four five okay now brachial plexus you can tell from its name brachial that it's going to probably have to do with nerves that Supply what muscles Breaky eye has to do with what the arms yep the arm so these are going to be nerves that Supply muscles like somebody said but to the arms specifically that's what brachial is telling you so the roots that form the brachial nerve brachial plexus are going to come from C4 through to T1 they're going to supply to the shoulder and upper limb this was chest and neck now we've got shoulder and Upper Limb and they're going to have names like they form nerves like the axillary nerve axillary nerve is the nerve that travels through the armpit um median radial Nar nerves you're familiar with radial and olar nerves they're going to travel down on the radial and allner sides of the forearm and other ones along those lines so these ones are important for motor activity and Sensation from the shoulder and the upper limbs basically if it travels through an area it's going to supply the muscles in that area okay now we skipped through the thoracics the thoracics don't really form uh plexuses other than contributing to the brachial plexus and we'll see they contribute to this next plexus a little bit otherwise the nerves that leave through the thoracics follow the ribs so the next plexus is down at the lumbar area lumbar plexus and this is made up of roots from T12 to about L4 okay and these are going to provide Sensation from the skin to the muscles of this region abdominal and pelvic areas and probably the a big nerve to be aware of here is the femoral nerve which is made from the nerve roots of L2 3 and four is a major nerve to the anterior thigh to the quadriceps so that's a major nerve that's formed from the lumbar plexus then we have the sacral plexus the sacral plexus is made up of nerve roots l45 and s123 and this is going to the nerves that come from this plexus are going to supply the gluteals remember gluteus medius Minimus and Maximus and the biggest nerve in the body is form Med from this sacral plexus the sciatic nerve and it's made from all of those nerve Roots we just mentioned l45 S12 and 3 it's about as big as your thumb in diameter and it travels through your butt and if you're a nurse who's going to be giv giving somebody an injection in their butt you better know where that sciatic nerve is because that atic nerve is big and it's an easy target and if you stick a needle into it your patient is not going to be very happy so to give you an idea of what I'm talking about here's a sacrum and we're going to put our anatomy over top of our sacrum I don't know if you can catch what I'm drawing here that's your backs side so basically they I'm drawing the gluteal muscles but we said the sciatic nerve comes from branches of l45 and s123 S1 23 and L4 and L5 and it forms as a big big nerve that runs down the back of your leg and IT supplies the whole lower limb except for the anterior thigh that the femoral nerve we mentioned in the previous plexus is responsible for so if you're a nurse and you're ready to give somebody a needle in their backside it's a good idea to take the in this example here we're looking at the left side and make a mental drawing of a quadrant in other words take half the butt divide it into a group of four and the upper outside quadrant is your safest place to give an injection because it's the one place that the sciatic nerve is probably not going to be but you can see the way that we've drawn this is that it's possible that it's going to be in all the other three quarters you follow follow me on that yeah so in your career you're going to be given injections you want to remember upper outside so that your patient doesn't get very mad at you or upset at you for you know hitting them literally where it's going to hurt sir could you go back to the sacral plexus y yep thank you so in our sacral plexus it's literally made up of all of those roots that we saw or sorry the sciatic nerves made up of all those roots now the nerves there's also not just nerves to the glues but nerves to the the external genitalia and the muscles associated with the anus and so on in that area too think of just what's in that region generally and you can predict that that these are the nerves that are going to be supplying those areas I have a question so there's a like a huge gap unless I wrote it wrong between the bracho plexus and the lumbar plexus like it the bracho plexus ends at T1 and the lumbar starts at t11 so what happens to like the t2 to t11 okay so I did mention that I me mention that the thoracic nerves follow the ribs they don't form Network so what they're going to do instead is follow a rib so what they'll look like um is if we had our vertebrae in [Music] here if our vertebrae was here okay and remember we said our ribs they travel like this they went backward first and then they came around the front to the sternum right yeah so when spinal nerves in the thoracic spine leave the spinal cord what they do is they come out and there's a branch that goes around behind and supplies the skin and muscles On The Backs side and then the anterior Branch travels forward to the front and IT Supplies the skin and the musculature that it passes by as it travels through that thoracic area so if we looked at the if we looked at the sternum from the in the anterior pit in the anterior pituitary and I'm getting into the endocrine system already there's our sternum and here's a rib and here's a rib and here's a rib they would each have a nerve that travels just inside the rib so it's protected by the rib but it branches and supplies everything through the thoracic cavity awesome thank you so much okay so they don't they don't Network they don't Network they just travel as individual nerves with the ribs so with spinal nerves then they're going to be associated with the spinal cord outside of the skull and cranial nerves are found inside the skull um you know what I don't want to talk about cranial nerves right now what I want to do is put together what we've been talking about so remember we said that the whole nervous system can be organized into boxes and arrows right that's the whole nervous system right there by now we know how to fill in everything we don't have to write it out every single time but we can refer to it so here what we want to do is we want to put together a real life example of what this looks like so let's see if I can um draw for you a good example of what we're talking about so there's a patella okay here is okay so can you tell what part of the body I'm drawing here anybody have any idea what I'm drawing here yeah it's a okay good so you can tell so what joint have I got pictured in here knee joint yeah it's the knee joint right yeah okay good so we know where we are now we want to put in a receptor so what we're going to do put put a a structure in there and we're going to put in we're going to draw in a reflex Hammer now some of you have maybe had this done to you in a doctor's office some of you maybe not have you ever had a patellar tendon reflex test done yes okay so you know you get a reflex hammer and you tap the tendon and what we're going to see is that this receptor is connected to a nerve that's going to travel back to the spinal cord and when it enters the spinal cord now we can so this represents our dorsal root and our dorsal root gangon right everybody okay with that this is taking the sensory information back to the spinal cord now in a deep tendon reflex also known as a stretch reflex the beauty is integration is as simple as you can possibly get in the nervous system because there's only one synapse in the whole nervous system for integration so what that means is that when we carry on into the spinal cord there's only one synapse that we need to worry about what color am I going to make that and it's going to leave to supply the quadriceps so now we've completed a picture here that has all three boxes and all Pathways to two arrows and it represents a real time integration organization all the components of the nervous system are represented here so we start this process by tapping the tendon on the patella so our reflex Hammer Taps the tendon on the patella and then we send an AER sensory signal into the spinal cord that synapses on directly on the motor neuron and comes back out again and what's what happens anybody who's ever had this done knows the patellar tendon gets tapped and what does your quadriceps do uh you extend your leg right because the quadriceps did what contract contract contract yeah contracted so it's known as a stretch reflex the stimulus was a stretch and the response was contraction so that's an awful lot like stretch contraction stretch contraction what is that looking a little bit like homeostasis ah there we go homeostasis good old homeostasis everybody loves talking about homeostasis well maybe not loves it but guess what it's part of what we do so let's try to label and we've got an aent pathway and we've got an e faren pathway so we have five segments here can we mimic can we map those same five segments on our real life drawing here so for example where would where would we put our receptor is it the tendon um the tendon here where the pen Mark is yeah okay well that's going to get stretched is it represented by being connected to the nervous system would it be the point of contact skin you mean from the hammer like with the hammer like to the skin okay so my question I always hope somebody will bring the hammer up as a stimulus because then I say do you think that human beings have Hammer receptors no right so and I nobody really said that nobody was thinking that but I bring it up anyway because it's called a stretch reflex so guess what the receptor is going to measure stretch yeah stretch and that stretch receptor is what I drew in this little rectangle in this space right here and it's connected to our aper pathway so this is our receptor and it is a stretch receptor so the stretch was caused here when the hammer tapped the tendon it pulled on the patella which pulls on the muscle but the receptor itself is located in the tendon of the muscle not the ligament so we have to be anatomically accurate there okay and then what is our AER pathway that's pretty straightforward right that's this one and where's integration it's like in the final cord where the synapse is like right here right that's integration mono synaptic mono synaptic one synapse so what's the eerm pathway what color the yellow one and our refector the quad yeah so we have all five components of the nervous system represented in this spinal reflex so spinal reflexes and spinal reflexes are primitive right spinal cord integration is very very simple so it's basically it's sort of like you're all or none you got sensory in motor out there's no refining there's no smoothing it's a very exaggerated response but it indicates that all your components in the nervous system are working that's why this becomes a basic part of a physical examination especially in um offices that are measuring nervous system function or muscular function function and that sort of thing so you can do deep tendon reflexes stretch reflexes down here at the Achilles on the patella in tendons of the arm in tendons down by the ankle and and you can in each of those cases determine whether the five segments of the nervous system are functional it's quick it's predictable it's reproducible so it becomes an important part of a neurological exam especially so let's take a look at another type of spinal reflex that one was called a stretch reflex now see if you can tell me what I'm drawing this time so let's uh let's do a it's a hand it is a hand okay that's good I'm gonna put that finger out on a little bit of a Bend okay now so we're going to put in whoops and what we're going to do here is put in a muscle and we're going to put in a muscle over on this side as well so you know we're going to add in a little bit of complication here I don't know what'll happen here so what I'm just trying to do here is show you the bone but we can appreciate that we've got muscle on either side of this joint we got a muscle that passes in front of the joint we got a muscle that passes Behind The Joint so we know those movements are going to be opposite of each other right yes okay so what did I try to draw down here what's that supposed to be down there a thumb tack yeah that's a tack okay so what we're going to do is we're going to do the same thing we're going to have a pathway that enters the spinal cord so here's a cross-section of our spinal cord white matter gray matter okay everybody with me so so so far we have our receptor what kind of receptor would this be sensory what kind of sense pain that's right this is a pain stimulus and a pain stimulus is going to cause what we hope will be a withdrawal reflex so it's another example of a spinal reflex so we know that it's going to be basic or primitive we know that it's predictable and we should be able to reproduce it so when we call it a withdrawal reflex what do you think the goal is going to be to pull pull away your hand right and in this picture what are we going to do to pull away we're going to have to do what what to Pardon Me contraction of what muscle biceps right the B which is this one right in our picture we're going to shorten that in order to go away from the tack that's what our goal is so what's going to happen is we're going to synapse on a motor motor neuron that goes to the biceps right and what's the neurotransmitter called that's released to the biceps to cause contraction AC and it was excitable right it caused contraction so we can put an excitable sign there remember at the beginning of today we talked about excitatory and inhibitory this is why I brought it up back then so how is it that the neuron that is going to deliver excitation to the biceps is going to have to also inhibit the triceps so what has to happen is we have to synapse on an intermediate neuron I can't actually put it on that side um let me get rid of that it's got to come down here on a different motor neuron so this one is going to go to the triceps muscle okay okay now I don't know if you can see that very clearly can you see that okay that I drew in a a a middle a neuron in between the two in green yeah okay so that's an interneuron it's going to be an inhibitory so the synapse so let's go back to the biceps for a minute the synapse between the sensory neuron and the motor neuron just like we saw for the stretch reflex is monosynaptic and it's going to be excitatory right because we want to get contraction in the biceps and we know that it's excitatory at the muscle so that we get contraction now the motor neuron stores acetylcholine AC so if it releases AC at the triceps the triceps contracts too and if the triceps and the biceps both contract at the same time what's going to happen to withdraw nothing nothing that's trouble right we want to withdraw so we somehow have to inhibit the triceps so that happens with this intermediary interneuron it has a different neurotransmitter so it blocks the transmission to the motor neuron that goes to triceps so triceps relaxes while the biceps contracts Let's see we got an extra neuron in there in order to change that message if we inhibit the motor neurons to triceps we get no signal no signal means no contraction does that make sense yes now question I just drew in another interger on here uh which actually I shouldn't do that let's just leave it like it is so now remember we said that the the stretch reflex was monos synaptic how many synapses do you see in this integration so Integrations in this in this case is in the spinal cord so you just need to count the synapses in the spinal cord three three that's right so now we're no longer monosynaptic right it's gotten a bit complicated so we see with the withdrawal reflex that the integration is a little more complicated but the goal is still very very basic it's still protection right in this case the stimulus was pain and the response was withdraw in our previous example the stimulus was stretch and the response was contraction looked a lot like homeostasis in the case of pain that's a little different it's not going to be something that matches up with homeostasis in that case but it is it is a survival reflex and it is in some ways it is reversing the stimulus cuz you're removing the stimulus right when you lift away from that tack but again we can if we if we want to look at the components of the nervous system again they're all represented here now let's just do it by numbers 2 3 4 five okay so where is number one in our diagram number one is receptor so where's our receptor bicep our receptor is going to be bicep the hand uh well let's be a little more specific the palm of the hand what about the palm of the hand pain pain pain what pain what what's this box pain receptors oh receptors oh box one's a receptor oh yeah yeah yeah that's what he's talking about yeah now I get it that's our number one where's our number two you know I'm having fun right I'm not mad can't tell sometimes through the through the computer what's number two is it the blue line that don't say is it the Blue Line it is the blue line and number three is going to be where just just say where it is where is it happening the spinal cord right and specifically gray matter or the spinal cord right if you were asked this on a test tell me it's the gray matter in the spinal cord because that's where the neurons are right so that's where integration would be and number four is represented in this case got to be careful here number four is represented where the yellow line and and the pink that's right and now for the person who answered first at the beginning incorrectly can now answer where would the affectors be biceps biceps [Music] and and triceps that's right perfect so do you see how the organization works when we start to put it into a real time picture picture yes I sort of think in fact I a little more than sort of think this would be a really good thing to remember being able to put these five components onto a real scenario either a picture that looks something like this or a picture that looks something like that in either case we can put uh let's see something that's going to show up right that's our our number one was our receptor our number two was our aper pathway this circled area here was integration number three our epher pathway was number four and our quadriceps is number five 1 2 3 4 four five see it yes perfect very good all right so that up to an including spinal reflexes will be on test number three