hey everyone welcome to professor long selectors in anatomy and physiology I'm professor long as you guys know when this coronavirus shut down so my face-to-face class has been switched to online and because of this short amount of time that we have and the delays that have gone on we are trying to get these videos cranked out so I don't have time to learn all the software I'm not a real computer guy so I'm doing these crude videos very quickly to get them out to my students they're all single tank so I'm doing the best I can to try to be as clear and concise as possible they're not coming the way that I like but I guess they're good enough the students have been sending me some nice messages I'm doing this at home in my dining room so every now and then if I look off there might be a kid or a dog or a cat doing something I get distracted I might fumble on my words and lose my train of thought a little bit please bear with me I'm doing the best I can and the timeframe that I got I wish I could go to an isolated studio and do some really nice videos and everything nonetheless this video is intended for students taking my human anatomy and physiology one course at Del Mar College we are following along in my notes set I'm going to be on page 89 we're going to talk about what a nerve plexus is and we're going to talk about reflexes it's an important concept especially for a lot of you guys in nursing Oh TA and PTA we're going to be you're going to be dealing with a lot of this neuro stuff for sure so if you want to follow along in the note set all the information is written there for you I'll be putting out a worksheet from this note set then you'll have to fill in some blanks and work on it's going to help you focus on those concepts that I want you to pay attention to the spinal cord as you saw in the first video on the spinal cord is not too complex as far as the anatomy and the layout it gets very complex when we start dealing with the input and the output from the spinal cord the efferent or sensory information coming in and those pathways and the efferent or motor pathways out there a little bit crazy and how they go and one of the things I would really like for you all to focus on from the last video which is the second one on the spinal cord which is all that motor and sensory pathways is where does the dorsal ramus monitoring posterior wall what is the ventral ramus monitoring and front sides and limbs or anterior wall lateral wall in the limbs the autonomic ganglion is monitoring or the autonomic nerve is carrying information in from the entire ventral body cavity it's also going to carry some axons out to the ventral body cavity know that all visceral motor pathways have to go to the autonomic ganglia on first if they're going to go out to the viscera of the back then they go out the dorsal ramus if they go to the viscera of the front sides and limbs out the ventral ramus if they're going to go to the thoracic cavity then they stop at the autonomic ganglia and the postganglionic fiber will go out the autonomic nerve all of the synapses utilize the cela choline except for the autonomic nerve going to the thoracic viscera uses adrenaline to increase heart rate increased breathing rate dilate Airways if we're gonna go to the abdominal pelvic viscera then the neuron does not stop the autonomic ganglia on the preganglionic neuron comes from the lateral very Horn of the ventral root all the way out the white ramus the autonomic nerve all the way out to the wall of the game the gangway on in the wall of the target organ the intramural game you know I'm gonna get into a little bit more detail on thoracolumbar and craniosacral so all of you guys that know this stuff backwards and forwards if you're gonna send me some criticism of well it's not really like that you didn't talk about the sympathetic chain ganglia and the collateral ganglia and the vagus nerve and craniosacral thoracolumbar all this terminology I'm gonna explain all that in the end I was trying to set the premise and then we're going to learn the differences later okay so one of the things that so I had to text my wife back one of the things that we need to talk about is that what a nerve plexus is so if I took a section of spinal cord let's just say the cervical reason region I have all these dorsal root and ventral roots coming together and I have all these nerves these spinal nerves and on occasion different levels of the spinal cord will have to go to the same location let's say I'm going to go to location one over here some part of the body well if all of these nerves are receiving input or from that location or sending motor commands out to that location I don't want to have to have every nerve have branches going to multiple places so what happens is they'll all sort of meet up at a little hub and then they can send axons out from there to multiple locations together so I might have four of these nerves sending axons out to location one two of them going here and two of them going here so all of these nerves how to get woven together into a network well the word plexus means network essentially so we call this a plexus a collection of nerves where they all meet up and then send information out and if you're following along in minor notes set at the top of page 89 80 it explains all of that it says that a plexus is a network of nerves that innervate a specific region of the body so one of the things that's gonna happen is we're gonna have several different Plex I all up and down the spinal cord we're gonna talk about the cervical plexus the brachial plexus we'll talk about the lumbar and the sacral plexus okay so if you follow along in my notes said I have a little table here on page 89 the cervical plexus has a bunch of Center get innervate parts of your neck obviously in the cervical region but one of the major nerves that comes out of the cervical plexus is going to go down and innervate the diaphragm as you know the diaphragm keeps you breathing the nerve that goes to the diaphragm is called me phrenic nerve the phrenic nerve innervates your diaphragm keeps you reading it comes out of the cervical plexus so you need to know the cervical plexus innervates a lot of the muscles of the neck but one of the structures it innervates also is the diaphragm and if you look at the cervical nerves if we were to start counting the cervical nerves see one two three four and five there's actually a little saying in emergency medicine that says and if you're going to be EMT paramedic or you're gonna work in an emergency room you'll hear this see three four and five keep the diaphragm alive it's a little saying that they teach an emergency medicine see three four five keeps the diaphragm alive so very often you might hear someone breaking their neck and dying pretty instantaneously or within a few minutes if you break your neck and you share the roots of nerves three four and five where the roots of the phrenic nerve are then you're not going to be able to breathe and you can pass away if you break your neck and you don't share three four and five then the diaphragm can still be functioning and you're perfectly okay or you might have some other paralysis or other issues and other nerves have been torn but you're not going to stop breathing okay so know that the phrenic nerve comes out of the cervical plexus the cervical plexus innervates a lot of the neck muscles and throat muscles but also see three four five those those nerves come through the plexus and they go out the phrenic nerve to your diaphragm some interesting information all right so the next plexus we're going to talk about is the brachial plexus now the brachial plexus since you should know by now if you don't you need to really consider retaking this course the brachial region is the upper arm so the brachial plexus is going to innervate your arm and it has a lot of muscles for the shoulder girdle and for the upper part of your arm and then there's two other nerves that branch out of the brachial plexus and if you remember when you look at your forearm your radius is on your thumb side and so there's a radial nerve that comes out of that plexus that innervates this side and then there's an ulnar nerve coming off the other side okay your pinky side remember your thumb a ride on your radius smell your pinky pee you pinky older so the ulnar nerve is running on this side of your forearm the radial nerve is running over here one of the things that we know is that the the radial nerve innervates a lot of the extensor muscles of the wrist so lifting your wrist up like this and an extension or hyperextension the ulnar nerve does a lot of the flexor muscles so if someone can actually push down on their wrist really hard but they're real weak pulling up then you know there might be damage to the radial nerve okay because the extensors aren't functioning properly now if the extensors are normally strong but the flexors are weak maybe there's damage to the ulnar nerve or at the spinal cord where the roots of these nerves are coming off to the towards the brachial plexus so you need to know the brachial plexus innervates your shoulder girdle and arm and the radial nerve which comes out of that plexus does the flexor I'm sorry the extensor muscles radial extension all nerves flexion we used to say this ER fu ER extensor radio if you flex our owner that's how we remember it all right so now let's go to the next plexus that's the information you need to know about that plexus for my class okay the lumbar plexus which is in your lower back is going to innervate a lot of your thigh region okay the upper part of your leg one of the major nerves that comes out that is called the femoral nerve or some people say femoral nerve well femoral means where your femur is it's the thigh region Kate the sacral plexus so this is a lumbar plexus contains the femoral nerve which goes to the femoral region your thigh area the sacral nerve goes to the lower leg the crus and the stirrup or your calf and your shin and two of the nerves that are going to run through there that come out of the sacral plexus one of them is called the sciatic nerve if you have problems with your back and you've heard of sciatica that is paying down your leg it can cause things like foot drop and problems because it innervates your lower leg and the muscles that control your ankle and your foot so know that the sciatic nerve for the lower leg comes out of the sacral plexus there's one other nerve that comes out sorry called the pudendal nerve the pudendal nerve innervates both the anal and urethral sphincter so when someone damages the lumbar plexus if they can't control you sorry I dropped something and then I knocked over the old marker board I used to use the anal and the urethral sphincter or sphincter muscles that the anal sphincter obviously holds waste in and the urethral sphincter in the urethra which holds urine in are under partially under voluntary control sorry there is a part of an involuntary and voluntary the internal and end the internal anal and urethral sphincter are under involuntary control you can't control those and when you when the bladder is full or when the rectum and colon are starting to fill and fill pressure then there's an autonomic reflexes the internal sphincters that's when you have to go oh you better get somewhere to release this stuff or it's going to embarrass you so you have some control over the external anal and urethral sphincter and that is through the pudendal nerve so people damage the sacral region they can have problems with their feet and if they damage the roots of the pudendal nerve they can have problems controlling their bladder they would have bladder incontinence they have to have a catheter and and they can't go to the restroom and control it because it just leaks out of them all the time or they may have to have a colostomy bag where they stick a tube into the colon and let the feces leak into a bag and it has to simply be emptied okay um one other thing before I get to the reflexes is I want to talk about two things so if we're talking about a person's head all the way down for their upper limbs to the lower lives as you know the spinal cord is going to be coming down like this okay if we damage the spinal cord somewhere up high I would cut off communication of all four limbs with the brain that leads to a term called quadriplegia Quadra from four and preach' a quadriplegic someone who has quadriplegia is someone who cannot control remove all four limbs they're paralyzing all for them usually if the damage is lower then you have someone that would be a paraplegic or they would have paraplegia meaning paralysis to a pair of limbs to Quadra is all four are paralyzed paraplegic would only be two limbs almost always paraplegics have lost the use of the legs I do know of one rare instance where someone damaged the nerves coming in and I read about this when I was a narrow student in graduate school where there was a a paraplegic of someone who couldn't use their arms but their legs were functioning which was kind of odd but it's because of the unique type of damage they did to the motor output to their arms and the sensory input to the arms only they damaged just specific it was a freak situation I can't even remember the details but usually when we say paraplegic you've cut off communication to the lower leg quadriplegic means you've cut off communication on all four limbs excuse me finally reflexes so let's get to the reflexes now this is where it gets a little confusing this information is pretty straightforward part of the reflexes is pretty confusing so bear with staring at my back for a moment and let's talk about this okay so now I'm gonna draw a little person over here [Music] arms legs just a small diagram okay and imagine if we could draw them in half now if I were to look at the spinal cord I'm going to draw a simplified version of the spinal cord I'm not even going to put all that stuff in I'm just going to do this okay we have the dorsal root the dorsal root ganglia on the ventral root and we have all the spinal cord here okay [Music] so we have the gray matter and all the horns here okay now we're gonna have things that are called reflexes the definition of a reflexes or reflex is an automatic motor response that is designed to preserve homeostasis so any reflex is an automatic motor response our body does it without us consciously controlling it these are all involuntary so to speak or some of them are voluntary but they're at such a low level of consciousness that they kind of bypass the brain temporarily we automatically do it to protect our body to protect us and then we figure out what happened it's the old theory sort of a shoot first and then ask questions later if someone's attacking you you might shoot first and then figure out okay what was going on so it's kind of what our spinal cord does it's what our what our nervous system does to protect us from damage first and then figure out what exactly was going on and I'll give you a quick example I know if this has ever happened to you but the house I used to live in before our shower had a hot and a cold faucet and turn on the hot water wait for it to get hot and then you temper it with cold water to get the temperature just right if you turn on the hot water and then you get distracted by something and forget that you never turned on the cold water and you go to test the temperature you stick your hand in and pull your hand out and then you feel the heat sensation set in well that's the shoot first ask questions later you pulled your hand out and then a fraction of a second later you realize oh that's hot so what we did was we bypassed the brain through the spinal cord to get a motor response at the same time that the information was going to the brain so we could figure out what happened and what to do about it in the long term so reflexes are a quick automatic motor responses designed to preserve homeostasis okay to protect us the pathway that they follow is called a reflex arc some of them are simple some of them are complex but if we look at a 3 flex arc a simple reflex arc would be simply B this pathway okay and I hope you can see this diagram pretty well let's say I have a sensation I stick my hand I you know I touch a hot stove and I pull my hand away well we're gonna have a neuron come in that's going to be a sensory neuron it's going to synapse to the spinal cord and then I'm gonna have to have some kind of central processing and I'm gonna have a motor command come right back out to the muscles to the effectors okay so it's really going to give us five steps that are gonna happen here so we're gonna detect the stimulus at a sensory receptor this is my abbreviation for the words detect a stimulus at the sensory receptor tape so we activate a sensory receptor and then we actually activate the sensory neuron and carry the action potential into the spinal cord so that's activation of the sensory neuron the receptor detects it the sensory neuron carries the signal to the sim to the central nervous system the spinal cord itself now we have some kind of central processing going on but again this is at the spinal cord level bypassing the brain temporarily so there's information processing is the third step if you're following my notes that on page 89 the steps are numbered the fourth step is going to be activation of your motor neuron we're going to activate the motor neuron and the last step is we get the response at the effector okay so you should know the basic steps of a reflex are what are the steps in correct order detection of the sensory stimulus stimulus at the sensory word receptor cell we activate the sensory neuron we do central processing activate the motor neuron and get the response at the effector okay now there are some really simple reflex arcs and there's some really complex ones okay so if you go onto page 90 there's some definitions at the top and these definitions tell us about different of reflexes one is called an innate reflex no if we look at this word innate the name comes from nature or Nestle's which means birth and furniture so innate our inborn reflexes we are born with these reflexes one a good example is the blinking reflex or the suckling reflex if you take them a little baby that's pretty fresh and you touch its face if you do this to an adult they can keep their eyes open and stare at you like why are you touching me if you do it to a baby they will blink every time because it's a reflex to protect their eyes from damage so they're born with that blinking reflex or if you touch their lips they try to suckle or chew on it the feeding reflex those are born in born reflexes or innate they develop during or prior to birth the next one on the list is called the acquired reflexes in acquired reflexes in order to acquire them you have to learn them to experience so acquired reflexes develop after we're born and as we're experiencing life we acquire them things like learning to walk if you take a fresh baby and stand them up boom they fall over so just standing up and balancing when our body senses that we're starting to go one way we naturally contract muscles to hold up our posture in our positioning walking riding a bicycle all of those things are acquired reflexes your balance so speak cranial reflexes always involve cranial nerves so as we talked about in the last quizzes in the last section on the brain if you hear a loud noise you turn your head towards it that's an auditory reflex that's a cranial nerve if you turn your head in your head towards something moving in the periphery if your pupils dilate or constrict and bright or dark light or vice versa those are all cranial reflexes they involve cranial nerves salivation when you think about food spinal reflexes involves spinal nerves and those are going to be a bunch of the ones that we're about to talk about but they involve any kind of things that pulling your hand off a hot stove things that involve spinal nerves somatic reflexes involve skeletal muscle like pulling your hand off a hot stove there's not only a spinal reflex it says somatic reflex because their skeletal muscles involved and then visceral reflexes involve our viscera okay so you know there's a reflex that once you start chewing food and tasting it and swallowing it your stomach starts to ramp up its activity so even if I just start talking about food you'll start salivating it's the muscle and salivary glands are smooth muscles so that would be a visceral reflex we're part of the digestive tract now so anyway you understand those definitions innate means you're born within develops prior to birth acquire develops after you're born through experience cranial involves cranial nerves spinal involve spinal nerves somatic reflexes evolved skeletal muscle and visceral or autonomic reflexes involved smooth and cardiac muscle okay now this is where it gets a little bit tricky and I'm going to erase my spinal cord here and redo all of this and we're going to do this about four or five times probably but I need you to understand some terminology and those of you that do OTA and PTA and even if you're going to be a nurse you're gonna deal with this if when you do your neuro rotations and those of you they do a lot of rehab are gonna need to know some of this some reflexes involve a single synapse in the CNS they're called monosynaptic reflexes mono meaning one polysynaptic reflex has involved many synapses several and they're much more complex okay so I'm gonna give you an example of monosynaptic reflex a good example of a monosynaptic reflex would be like what we call the stretch reflex so when you go to the doctor if you're sitting on a table and your knee is like this and they bang you with that little hand on the patellar tendon and your mag kicks out that is a monosynaptic reflex it's a rather simple one I hope you can see that my black marker is giving out I'm about to start using different color so when it comes to our spinal cord here and I'm not even going to draw the roots okay I'm just going to draw a simple spinal cord like this what's going to happen is we're going to feel stretching that tendon the axon will come in the soma lives in the dorsal root ganglion and it's going to bypass here and synapse on a motor neuron and that motor neuron is going to go out to your extensor muscles and fire and excitedly on them and they're going to kick and extend your leg what happens is if we stretch that tendon it would be like if you're folding your leg back if you over stretch it and tears the muscles you would not be able to hunt or find food and so therefore we need to reverse that quick stretch so we fire off and extend our leg it's considered a monosynaptic reflex because we have a single synapse going on okay now there's another term that you should also know called FC lateral if c comes from the same word as ISO which means same and lateral means side it's a lateral reflexes means that the response the motor response happens on the same side of the spinal cord as the stimulus so when they bang on your right patellar tendon you don't kick your left leg you kick your right leg out also so that's also an ipsilateral reflex it's monosynaptic because there's one synapse it's called the stretch reflex you bang on a tendon and they do the same thing in your arm and there's a another one called the Babinski reflex and babies but there's another a number of monosynaptic reflexes and they're always Epsilon okay now polysynaptic reflex is R where it gets complex now polysynaptic reflexes are going to be called contralateral also all polysynaptic reflexes are usually well not all of them polysynaptic reflexes can be hip salata or contralateral and let me give you an example okay so I'm going to talk about polysynaptic and the first example that I'm going to give you a little polysynaptic reflex it's called the withdrawal reflex the withdrawal reflex is not only polysynaptic but it is also it's a lateral meaning that response is going to happen on the same side if I put my right hand on a hot stove there's no reason for me to start jerking around my left arm I want to withdraw it from the same side okay so this involves the upper limbs and this is considered to be an ipsilateral reflex because it's going to happen on the same side but it's going to be polysynaptic and here's why okay so if I put someone's hand out here and here's the arm the elbow remember I'm going to have muscles over here and on one side of the arm I'm gonna have flexor muscles on the other side of the arm excuse me I'm gonna have the extensor muscles so if I fire my biceps muscle I will flex my arm if I fire the triceps muscle I will extend my arm well in this reflex when I withdraw my hand from a hot stove I'm gonna flex my arm okay now here's my spinal cord anterior posterior and so on okay what's going to happen is when I sense this it's a sensation and I'm not going to draw it coming through the arm because I want I don't want to make this too messy but the sensory neuron is going to come in and senesce it's going to stimulate what's called an internal an interneuron inter neurons or neurons that are in between two others intervening between and they're always in the CNS and there'll be two inter neurons that fire one's going to fire here and then I'm gonna have a motor neuron that would come out through the through the and your great horns and Caesar or somatic motor but it's going to come out this way and what's going to happen is these are going to be excitatory meaning I'm going to fire and make the muscles contract but in order to do that I have to make sure I inhibit the extensor muscles and so another synapse will come around here and the inhibitory and it's going to inhibit this muscle from firing now you can see while they're called polysynaptic there's a bunch of synapses going on here okay the entire effect is going to happen on the same side of the body so we call this a withdrawal or a flexor reflex I'm gonna flex my arm or withdraw my arm and I have to excite which is why we call it reflects our reflex I excite the flexor muscles and I'm going to inhibit the extensor muscles so the withdrawal reflex is also called the flexor reflex okay because we're gonna flex our arm it is polysynaptic i'm going to excite the flexor muscles i'm going to inhibit the extensor muscles okay it's all EPSA lateral now we got a more complex one to do after that so make sure you get that information down it's all written on page 90 and my note said now we're going to do the last one that I want to cover which is called the crossed extensor reflex this one involves the legs if you're walking through the house and you step on a Lego or a kick a couch or table you want to flexor withdraw the side that was damaged but you have to extend the opposite side so that you have a foot to stand on while you hop around in cus so it's called a crossed extensor reflex got all this down I'm gonna erase this and let's do one more polysynaptic reflex and the crossed extensor reflex is going to be even more complex than this one and it's going to be contralateral okay so I'm going to use a different term here this is polysynaptic that is considered in the contra lateral contralateral means opposite side contra means opposite are against so to oppose so in a contra lat I made that on one word denied contralateral reflexes always involve a response on the opposite side of the body from the side of the stimulus if I step on a nail on this foot I want to withdraw this one I want to extend the opposite foot so crossed extensor reflexes are contralateral they involve the legs and there's even more synapses so look here's a knee and a foot here's someone's leg okay not the prettiest leg I've ever drawn but oh uh I'm not interested in here's the opposite leg okay now I'm gonna have my spinal cord here in the middle okay I hope you can see all that it's a crude drawing but you'll get this now the stimulus I'm not going to have the neuron go through the leg because I got to do some stuff here but let's say you step on a nail or you kick a table or you step on a hot coal or something in a barbecue and you're barefoot the sensory neuron is going to come in and it's going to fire there's going to be a number of inter neurons one inter neuron is going to be excitatory and it's going to cause excitement of the flexor muscles it's the same thing as your arm you're going to flex the leg on the same side as the damage so we excite the flexor on the same side of the damage and you flex your foot or lift it then means I'm also going to have to inhibit the extensor muscles so on the same side of the damage I get the flexor reflex I excite the flexors I inhibit the extensors okay but on the opposite side of the body I'm gonna have to do this I'm going to excite the extensor muscles this is why it's called a cross extensor reflex because on the opposite side on the contralateral side I'm going to excite the extensors so this is called the crossed extensor reflex it is an polysynaptic reflex that is contralateral I'm going to have extension on the opposite side of the damage that means I'm also going to have to inhibit the flexor muscles on the opposite side as well so in both of these you need to know what's happening so the withdrawal or flexor reflex involves the upper limbs I'm going to excite the flexors inhibit the extensors so that I can withdraw same thing happens here on on the crossed extensor reflex on the side that the damage occurs I'm gonna excite the flexors and inhibit the extensors so that I can withdraw the foot but if I did not have this I might may not have already transferred all my weight if I lift my foot I could fall so I want to extend the leg on the opposite side so I have a leg to stand on so I'm gonna excite the extensors crossed extensors got it alright listen that's a lot of information I know but you know we're nearing the end the next couple of lectures are not going to be anywhere near as difficult as these last two so hang in there keep pushing through keep working the notes to you can't stand it do the worksheets when I get them published and be ready for the quizzes in a week or so okay today is the 23rd I think we're taking these quizzes sometimes around the 29th or the the end of the month so you're gonna have at least a week to cover these videos and start working on them and doing the worksheets before we take the quiz alright thanks for watching I hope you have as much fun as I did see on the flip side