they also to finish up the spinal cord and nerves will do a bit on reflexes then we'll move into nerve Anatomy and finish with the nerve plexuses so when we talk about reflexes this is kind of building off of what we've finished with in the earlier spinal cord video when we looked at a cross-section of a spinal cord and how sensory information comes in give processed and motor commands go out but what is a reflex well it's a rapid predictable motor response to a stimulus a predictable so something the same always happens and it happens very quickly now remember motor can refer to any type of muscle movement or if a gland is activated and these are important clinically you can check for these on a patient to help you figure out whether or not there are certain nerve damage or neurological issues and we won't get into that much in bio 5 but in the future courses you may need to learn more about that you can classify reflexes as spinal reflexes and cranial reflexes and as some examples of reflexes you're already familiar with the patellar tendon reflex occurs when a physician taps you on the patellar tendon with a hammer will mallet for example and your leg kicks out although really what that's doing is just testing your ability to really like balance and steady yourself yeah so as you're walking you need these reflexes to suddenly like I don't know if you step on something and you lift up a foot immediately your other foot has to take that extra weight so that's the type of reflex we're talking about here withdrawal reflex is like the burning your hand on a hot stove and pulling your hand off we call the withdrawal reflex and the pupillary reflex is when you have a light shine into your eyes or you enter a break room and your pupils constrict and there's also something called the consensual pupil reflex which is if you shine a flashlight in one eye that pupil should can strict but so too should the other people that's the consensual pupillary reflex so all kinds of cool stuff there's lots of reflexes that you can learn about and in fact if you want to know about more a couple of those I just mentioned and you haven't found yet registered are in YouTube site it's pretty good she's funny ish and not as funny as I am and she has these videos on here you can see of course the pupillary reflex and the patellar reflex but well we'll talk about before we move on is that reflexes can be classified in many ways not just what we mentioned previously that there are spinal Refik reflexes and cranial reflexes but in lots of ways so let's talk about the pupillary reflex as an example the pupillary reflex is an innate reflex so it's built into our genes it's not something that's acquired or learned it's a visceral reflex or an autonomic reflexes automatically and when you think of things happening involuntarily you should be thinking Oh cardiac muscle is involuntary smooth muscle is involuntary and what our glands do is also involuntary so the pupillary responses and visceral reflex not a somatic reflex because that would involve skeletal muscle the pupillary reflex is polysynaptic it just means for shorthand you can kind of think of it as like it's not that fast there's multiple synapses that have to take place to deliver that message it's not as fast as a monosynaptic reflex which will just be two neurons involved in sensory information comes in and immediately with no integration no processing no thinking about it immediately response occurs that would be of monosynaptic reflex and then last because that reflex occurs in this process in the brain as is most of the reflexes involved in your face and head area that is a cranial reflex but if you think about this patellar reflex that's different in a lot of ways it still is an innate reflex but it's a somatic reflex because it's skeletal muscle it's monosynaptic it happens almost instantaneously and it's a spinal reflex because we're talking about stuff happening like if you step on something sharp and you have to take that weight on the other leg that's all occurring down in your spinal cord is where the spinal cord processes that information and sends out a very fast response although in this case it doesn't even process the information because it's monosynaptic so all of these are ways to categorize nerves reflexes rather and they're not mutually exclusive of course so each reflex you would basically pick from each column and you would say it's one of these or one of these or one of these are one of these when you think about the wiring in your body of reflex we call them reflex arcs and you have a sensory receptor on one end of this arc and an effector some kind of muscle or gland on the other end and reflexes take place in five steps that you can read through here but I'm going to pull up the diagram and we have our same five steps shown in this arc okay this is kind of like an arc shape we start with the arrival of the stimulus and activating some kind of sensory receptor in this case we've got a pain receptor being stimulated so the receptor will activate a neuron to actually carry that information into the central nervous system so here we've got that information coming in and look building off of our cross section of the spinal cord from before we can see all the usual suspects the h of gray matter the white matter columns the dorsal root ganglia and so on so when that information arrives number three is information processing so depending on the reflex you'll have lots going on here not so much going on here but the information is being processed in the central nervous system maybe in the spinal cord sometimes in the brain obviously this drawing is showing a reflex art of a spinal reflex because it shows the spinal cord is doing the processing and here we have this inter neuron that's going to help decide what to do here and you see a little branch going into the white matter so the inter neuron it's going to tell the brain what you're up to you it's also going to decide maybe to send out a motor command but it'll tell the brain what you did so if a reflex action is warranted the inter neuron will stimulate a motor neuron so that's step number four which will travel down to the effector and step number five to set their response by the effector in this case to remove your hand from that pain stimulus by flexing your elbow now remember of course this is just one kind of classic example of a reflex but you have these visceral reflexes happening all the time in your body you've got all this information coming in from your organs you don't even have to think about it this process is going on constantly and the infect effector might be some smooth muscle in your digestive tract it might be some reproductive function and it might be some glands being turned on or off and all of that is occurring in a similar manner okay let's move on to nerve Anatomy this is going to be pretty short and sweet we've talked about that there are 31 pairs of spinal nerves branching off the spinal cord eight cervical and twelve thoracic five each of a lumbar and sacral and you have a single coccygeal nerve so that's 31 total and if you take any one of these nerves and you look at these spinal nerves you'll see that there are bundles and bundles within the bundles and hopefully this is reminding you of muscle anatomy when we looked at a skeletal muscle we have a similar kind of construction so in this case the nerve is wrapped in a connective tissue layer called the epidermis muscles were wrapped in the epimysium and then when you cut open a muscle you found a bunch of fascicles and look at this here - these are fascicles we're using the same terminology so fascicles each fascicle is wrapped in a perineurium each fascicle and muscle was wrapped in a Paramecium and then if you open up a fascicle you see a bunch of fibers nerve fibers we just mean neurons uh axons of neurons so each of these nerve fibers is wrapped in connective tissue called endo Nerium each muscle fiber was wrapped in connective tissue called endo Museum so if you remember that structure of skeletal muscle tissue this should be pretty straightforward this is just a second diagram this is the new diagram from the book that we sometimes recommend I like the previous diagram better but here's just another way to look at it as an entire nerve being bundled made of a bundle of fascicles each fascicle being made of a bunch of axons of neurons nerve fibers and here's one single nerve fiber coming out one single axon with some Schwann cells on top okay our last topic is these nerve plexuses these are the branching networks of interconnected nerves and we're going to see what they look like but all of the ventral Ram I remember from previous video there's a drawing that showed a ventral ramus and a dorsal remus so all of those ventral Bream I have these nerve plexuses except the thoracic region does not and we'll see why and what that looks like in a moment so interconnected nerve so you've got one up in the neck one in the arm area one in your lower back and one down towards your sacrum and the advantage of having these nerves all intertwined is that if you sustained trauma or damage to one of those branches you still may be able to send sensory and motor information through a different pathway within that network so let's look at the cervical plexus first finding the first five pairs of spinal nerves this plexus innervates the skin and muscles of the neck and shoulder so that makes sense based on its name and we'll just learn one critical nerve from that plexus called the phrenic nerve phrenic literally means diaphragm and so it's going to and from the diaphragm to in front meaning it's bringing sensory information from your diaphragm and it's sending motor commands to your diaphragm right around c4 so if we look at that here here's the cervical plexus so that should look like to you an interconnected network of nerves and you can imagine perhaps that if any one of these little branches got cut you may be able to find a separate path to send that information and down here the phrenic nerve there's just a little information on here but it's repeating the fact that this nerve is headed towards the diaphragm and there's an old saying I don't know if it's an old thing there is a saying see for breathe no more meaning if you sustained damage in or about the fourth cervical vertebra you can affect this phrenic nerve and if you damage your sever the phrenic nerve you can't tell the diaphragm to contract and relax then you breathe no more here's a brachial plexus and it's kind of dissected out here in a cadaver view this plexus innervates the pectoral girdle in the arm and we'll talk about a few of these nerves but also the fact that this may look like kind of a mess but in actuality there's a organization here if you look on this diagram you can see that we start with these ram i and they follow this progression of branching and breaking apart and branching back together again and again and they form these trunks divisions and chords before you eventually get the nerves so if we look back here there are some trunks and some chords that you want to look at this is mainly for a lab topic but I put little boxes around the trunks superior middle and inferior trunk and a box around the cords lateral posterior and medial cord so you'll see these on lab models they're just the organizational system for this plexus and we didn't add on the the divisions there's even more different branches here but the point is eventually each of these are going to go to their own place in your pectoral girdle or upper limb and we don't care about all these nerves we just want to talk about a few the musculocutaneous nerve allows you to flex your arm and forearm as this name would imply it not only sends muscle commands but it's going to the skin actually bring sensory information back from your skin in your arm and forearm the median nerve innervates the flexors of the wrist and fingers axillary innervate some specific muscles deltoid and teres minor ok teres minor in the back of the armpit region the ulnar nerve innervates the flexors of the wrist and fingers and the radial nerve innervates the extensors of the arms wrists and fingers so you want to kind of think back to your muscle and/or bone days and try to trace these out in your mind as you look at your arms but realize also that as you learn what muscles are innervated by these different nerves you can well for one you can pretty quickly start to diagnose nerve damage if you knew all the nerves and everything they innervated oh yeah that's a lot but also keep in mind that you'll know that all these areas also have sensory information from the skin in those regions coming back into the spinal cord all of these nerves also carry since information back in so a loss of feeling in some parts of the body could also correspond with the loss of muscle control to those regions and here's a little bit more detail we just picked a little bit of what is innervated by each of these nerves but there's much more that you can look into you if you so wish we did say that there's no plexuses in the thoracic area but there are spinal nerves branching off the spinal cord down through the thorax so what are those doing they're just kind of branching out throughout your your chest region if you look at this image there's a bunch of those nerves labeled but I just really wanted to show you how that they are branching out there is innervation for your whole thoracic region and some of the things they're doing are for example being involved in respiration like your intercostal muscles you should remember learning about those assists in respiration they help the diaphragm so it's one of the things that these nerves do is they aid in respiration okay we've got a couple more plexuses we did cervical and brachial now we're looking at the lumbar plexus down in the mostly in the lumbar region and these nerves are going to innervate your lower abdomen and we're getting into parts of the thigh so we'll look at just two in detail the femoral nerve innervates the flexors in the hip and the extensors and the obturator nerve innervates the adductors of the leg now just like we've been learning before these nerves also are carrying sensory information back in from the skin and and from those regions and here's the lumbar plexus with all of the intertwining nerve networks shown in full lots of different nerves here in the list we're just looking a little bit at the femoral and obturator nerve and the functions of each and we finished with the sacral plexus down in the sacral region innervating the thigh and the vagus nerve in your body called the sciatic nerve is found in the sacral plexus so s4 sacral s4 sciatic and that big fat nerve travels down your leg and it branches into the tibial nerve which innervates the hip extensors leg flexors with flexors and toe flexors and the common fibular nerve does the extensors in that region again these nerves are gathering up sensory information from those regions and they're transmitting that back into your central nervous system so now we've looked at spinal cord anatomy we've talked about how reflexes work the anatomy of nerves and these nerve plexuses and started to study some of the specific nerves and quite a bit of this you will see is repeated within your lab models looking at the cross-section of the spinal cord looking at the nerve boards where you have a whole human figure and you can trace some of these nerves on there so make sure you're integrating this because of several chunks of this are kind of trending more towards lab type information although you'll see some references it to it in future lecture examinations as well ie