hello everybody so today we're going to be going over chapter seven part one chapter seven is extremely long so I have decided to break it up into two portions so chapter seven is based on the nervous system so as a primary control system of the body the nervous system provides higher mental function and emotional expression as well as maintaining homeostasis and it basically helps regulate the activities of muscle and glands within the body so communication by the nervous system involves a combination of electrical and chemical signals all body systems are influenced by the nervous system in some way right so if your nervous system stops functioning your body can still sustain life but that would be with us with an assistance of a life supporting machine so we may ask ourselves what is the nervous system what exactly does a nervous system do right and we can basically correlate this to our everyday lives you're in lecture right now or you're listening to this video at home while you're washing the dishes or watching the kiddos and you're really not paying attention to anything that I say right but as soon as I say your name you're automatically going to start paying attention to this whole lecture okay or you're in a meeting at work right and their meetings every Mondays it's a Monday you're really not paying attention you're just a warm body on the chair okay and so basically you have no idea what's going on in the discussion but as soon as you hear your name you right away turn around to the speaker in order to try to figure out or try to tag along on that conversation right so this is just a few ways that your body cells are constantly active all the time so the nervous system is a master control and communication system of the body every thought action and emotion is reflected by its activity these are immediate responses so we have the sensory input we have the integration and we have the motor output you've heard some of these already before right so your sensory output is basically sensory receptors that monitor change called stimuli right so stimuli is going to be anything that is occurring outside or inside of the body right it's a change within the outside or the inside of the body in which that stimuli is going to pick up and send a signal to the integration center now your integration says Center processes and interprets that sensory input and decides whether an action is needed or not right and if an action is needed then we have a motor output your motor output is going to be a response right or an effect that either activates a muscle or activates a gland right we've heard of these already right our sensory input is known as our what afferent right and our motor output is going to be known as your efferent no let's go back really quick I need to give an example so that you guys understand a little bit more about the nervous system right so here we have your eye okay your eye is a center receptor okay and so basically it's going to send a sensory input to the brain and the spinal cord okay your brain and spinal cord are located within your integration system within your C and S and you guys will learn about your CNS in just a little bit okay the brain and spinal cord decide that there needs to be a motor output right and so basically that motor output is sent and basically what we have is a stimulation of a muscle okay so another example just to give to you guys you guys are driving down the highway let's just say you guys are going down towards theater here in El Paso and you automatically see a red light right your sensory input is going to say red light it's going to send that into the um integration Center in which it's going to receive that information meaning red light means stop don't go and it's going to send a motor output to the muscles of your right leg and foot meaning that your foot is automatically going to press on that brake pedal right and that is going to be your response in order to stop so because of the complexity of the nervous system we divide it into terms of structure which is structural classification or in terms of activity which is functional classification and so under structures we have the central nervous system known as CNS and the peripheral nervous system which is going to be known as pns and under activity we are going to have your sensory which is Affair which we've discussed previously and motor which is efferent so the central nervous system receives input via sensory fibers and issues out commands via motor fibers right so here we have our Century which is a for and here we have our motor which is effect here we have our pns okay and here we have our CNS so the nervous system is organized and it basically follows a structure so information from Sentry or from sense orients okay or afferent information uh is going to be sent to your sensory afferent okay and this information is going to travel to your pns system through your cranial and spine nerves So within your PMS we have your cranial and spinal nerves okay the pns then sends information to your CNS which is your central nervous system that consists of your brain and your spinal cord okay the brain and spinal cord send back information to your pns so it's sending back that information to your pns which then sends a motor or as we know an efferent information to either somatic nervous system which is voluntary or that basically involves the skeletal muscle or the autonomic nervous system which is involuntary which involves cardiac and smooth muscles and glands okay so it's going to send a signal to your somatic to your Autumn autonomic somatic is going to be anything that's skeletal muscles autonomic is going to be cardiac smooth muscles and glands now your autonomic nervous system is further subdivided into parasympathetic and sympathetic systems which we'll go over further in further lectures now let's begin to discuss the structural structural classification of the CNS and the pns that includes all nervous system organs right and so when we look at the CNS we're going to be looking at this side which is going to consist of the brain and the spinal cord okay this is your CNS so the CNS consists of the brain in the spinal cord they occupy the dorsal body cavity and act as the integrating and command centers of the nervous system they function and basically interpreting incoming sensory information and is basically issuing out instructions now your pns is going to be right here so it's going to consist of your cranial nerves okay and your spinal nerves and so European Nest includes all parts of the nervous system outside of the CNS so your pns consists of the nerves that extend from the brain and the spinal cord which consists of the spinal nerves which carry impulses to and from the spinal cord your cranial nerves carry impulses to and from the brain okay so basically these nerves serve as communication lines among sensory organs so how does it work right they basically link all the body parts by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands are muscles in order to produce an action now the pns is divided into two principal subdivisions known as a sensory Division and the motor division okay now the century division or afferent division consists of nerve fibers that carry information to the central nervous system okay so the sun sensory division keeps the CNS informed of anything happening inside and outside of the body somatics sensory fibers carry information from the skin and so your skeletal muscles and joints and those transmitting impulses from visceral organs also known as visceral sensory fibers your motor division or efferent division carries impulses away from the CNS right so those are going to be the factor organs the muscles and glands so the effects brings out a motor response so the motor division has two subdivisions right the somatic nervous system and the autonomic nervous system the somatic nervous system is voluntary meaning we can control our skeletal muscles the autonomic nervous system is involuntary meaning we have no conscience control of what's going on kind of like the heart we can't tell the heart to beat it just automatically beats on its own this involves anything that is going to be smooth muscle cardiac muscle and glands now the ANS which is your autonomic nervous system is further divided into sympathetic and para a sympathetic nervous systems so let's start talking about nervous tissue and supporting cells so supporting cells in the CNS are basically grouped together known as neuroglia so what are their functions they help support insulate insulate and protect neurons so the structure and the function of each of these so the neuron tissue is made up of two principal cell types right one of them is going to be your neuroglia your glia cells or your glia just by itself right and so the second one is going to be your neurons so your supporting cells are going to resemble neurons but they are not neurons because they cannot conduct nerve impulses and they never lose the ability to divide right so neurons are going to be different than our supporting cells so what are the two main functional subdivisions of the nervous system you guys should have all chosen sensory and motor so let's talk about CNS remember that CNS is your central nervous system so we're going to be talking about you're seeing this glial cells so each different type of neuroglia has special functions within the CNS neuroglia include astrocytes microglia epine ependymol and oligodendrocytes okay so we're going to be focusing on your astrocytes so astrocytes are abundant star shape they're swollen ends cling to neurons so these are going to be your astrocytes okay these swollen ends that you see here are basically going to be the ones that are cleaning onto your neuron which is going to be in your yellow and it's basically bracing them and anchoring them to a to blood capillaries okay remember that blood capillaries what do they do they serve as nourishments right so astrocytes form a living barrier between capillaries and neurons that help determine capillary permeability but also protect neurons from harmful substances that might be in in the blood so they also control the chemical environment of the brain by basically mopping up any leaked potassium ions these are going to be your microglia okay they look like little spiders right so your microfilia are spider-like phagocytes that monitor the health of nearby neurons and Disposal debris such as Dead brain cells or bacteria what we see here are going to be your appendix cells and they basically line the central cavities of the brain and the spinal cord they participate in the production of cerebral spinal fluid and the Cilia assists with circulation of this fluid so here we have the brain and spinal tissue and here we have your fluid-filled cavity the next one within your CNS are going to be known as your oligodendrocytes okay and they basically wrap their flat extensions tightly around your CNS nerve fibers so these are going to be your nerve fibers that are going to be in yellow and basically what you see in the blue is going to be known as your myelin sheath okay and basically what happens is they produce fatty insulin and coverings as what we know as or what we know them as as myelin sheets now let's talk about pns glial cells Okay so there are Swan cells and acetylene cells so Swan cells form the myelin sheaths around nerve fibers in your pns and satellite cells protecting cushion neuron cell bodies okay so here we have your satellite cells that are basically going to be around that cell body of that neuron that is going to be protecting it and then here we have your nerve fibers that are in yellow and basically what we have wrapped around those nerve fibers are your Swan cells okay and so basically they're just forming myelin sheaths in order to help uh with that nerve fiber protect it right so neurons are nerve cells specialized to transmit messages right nerve impulses from one part to the body to another okay the word now we're talking about neurons right all neurons consist of a cell body which contains a nucleus and one or more processes that extend from the cell body okay so I've included this image here and this image that you see of this neuron is going to be included in three more slides and the reason for this is because it's just easier to get a better picture of it right so this is the neuron that we're talking about okay their neuron is going to consist of a nucleus which is going to be this region okay and it's going to consist of a nucleus okay now here we have these little lakes that are on the outside and these are going to be our dendrites okay here we have the cell body your nasal substance okay are going to be these little things right here but these are actually rough ER here we have your neurofibrils okay and they basically just help maintain the shape of the neuron here we have your Axon okay and in between this axon we're going to have what we known as your Swan cells right those myelin sheets and at the end of the axon we have your axon terminal so this is just a quick overview of the image that you guys see here of the neuron because you're going to be seeing it again pretty soon so supporting cells in the central nervous system are collectively called neuroglia right because we were talking about CNS not pns now let's further discuss the neurons so the cell body is a metabolic center of the neuron okay so it consists of a nucleus as we mentioned before with the with a large nucleus the rough ER is called the nasal bodies which I've already previously mentioned and the neurofibrils are intermediate filaments that maintain the cell shape right so we've already discussed what each one of these do here we have the cell body here we have the rough ER here we have the dendrites here we have the nucleus and the nucleus now this is just the structure of a typical motor neuron okay we've already gone over all of this right but this is just a motor neuron for you as a whole so if we go ahead and look at this under microscope right the neuron doesn't look like this exactly it looks something like this right here we have our dendrites that are basically connecting to other neurons and then here we have the neuron cell body so let's move on to the arm-like processes or basically fibers foreign so they are going to vary in length but they are neuron processes that convey incoming messages such as electrical signals towards the cell body and these are going to be known as dendrites so these are processing fibers and here we have our little dendrites that we've already discussed before so your nerve impulses that conduct them away from the cell body are known as accents right so here we have our accents basically all this yellow thing that you see going all the way down okay the difference between the dendrite and the axon is that neurons may have hundreds of dendrites and neurons consist of only one axon arising from the cell body at that Axon hillock okay so there's only one axon body but there's many dendrites now the end of the axon terminal contains the vesicles with neurotransmitters so here we have your Exon terminal these are going to contain neurotransmitters and I can't really write very well with this okay remember that axons transmit nerve impulses away from the cell body right so basically they're going away from the cell body when these impulses reach the axon terminals they stimulate the release of neurotransmitters into the extracellular space between neurons and each axon terminal is separated from the next neuron by a gap and this is going to be known as your synaptic cleft okay so basically these axon terminals are not touching the other cell bodies okay or the other axons okay and so the this Gap known as a synaptic cleft is going to be what is responsible for sending those signals between these neurons so the functional Junction between nerves where nerve impulse is transmitted is known as your synapse so let's start talking about your myelin sheath right so your myelin is a white fatty material covering axon myelin protects and insulates fibers and increases the speed of nerve impulses impulse Transmissions right so basically these myelin sheets are what we've already talked about before they're Swan cells right so here we have the swan cell nucleus that you see here here we have uh the swan cell plasma membrane and then the inside is the swan cell cytoplasm okay and so basically what they're doing is they're wrapping themselves around this axon okay so Swan cells wrap axons in a jelly roll-like fashion within your pns to form the myelin sheath okay your neuro Lima which is part of the Swan cell okay so here we have your neurolemia which is part of the Swan cell which is external to the myelin sheath okay so here we have right here and then the rest of this portion is going to be your myelin sheath okay forms knots of render which are gaps in the myelin sheath along the axon so oh sorry guys I want too much ahead okay they are these little knots that you see right here these are known as you're not of Ranbir not a red rear okay so they're gaps in the myelin sheath along the axon you oligodendrocytes produce myelin sheaths around axons within your CNS okay and they lack a neurolemia which plays a role in fiber regenerization so this is just a bigger image of what we just saw previously right a swan cell envelopes part of an axon in a in a in a uh and basically rotates around the axon most of the Swan cell cytoplasm comes to lie just beneath the exposed part of the of basically its plasma membrane okay as we see here the Thai coil the plasma membrane material surrounding the axon is the myelin sheath so that's what we're seeing here okay so what we're seeing right here is that myelin sheath that is wrapped around that axon okay the swan cell cytoplasm and exposed membrane are referred to as in the neuro Lima so this outer portion right here is going to be referred to as your neurolemia so remember that clusters of neuron cell cell bodies and collections of nerve fibers are named differently in CNS and in pns so here's just a couple a couple bits of terminology so when we talk about nuclei within the CNS or clusters of cell bodies okay when we're referring to ganglia they are collections of cell bodies outside the CNS in the pns okay when we talk about tracks They are bundles of nerve fibers in CNS so their nerve fibers in CNS and they're known as tracts when we talk about nerves their bundle of nerves that are found within the pns okay white matter which we're going to start talking about later on in part two is basically collections of Miley uh myelinated fibers known as Trax and gray matter is mostly unmyelinated fibers and cell bodies now neurons are grouped according to the direction the nerve impulse travels related to the CNS okay so there are sensory motor and Association neurons which are interneurons and so neurons that carry impulses from the sensory receptors to CNS are sensory neurons The receptors include cutaneous sense organs in skin and um and proprioceptors in muscles and tendons the cell bodies of sensory neurons are always found in ganglia outside of the CNS now neurons carry impulses from the CNS to the viscera and or muscles and glands or motor neurons the cell bodies of the neurons are usually located in the CNS your interneurons connect the motor and sensory Sensory neurons in neural Pathways so their cell bodies are typically located within the CNS now let's just go ahead and take a look at this really quick okay this looks extremely confusing but don't get confused this is stuff that we've already seen okay here we have the Axon okay here we have those dendrites okay that you see here these are going to be our receptors right they are going to be receiving receiving because it's our afferent pathway in red you're going to see dendrites as well but these are the effectors right they're either going to stimulate a muscle or gland and the red is going to be our efferent pathway right along these efferent pathway we have our motor neuron that is going to help deliver that message in order for that transmission to happen here we have the interneurons okay notice how they are not exactly connecting to one another right that's where we have the the synaptic cleft okay so your interneuron is basically an association neuron okay and they are located within your CNS CNS and that's going to consist of your spinal cord and brain right so here we have our sensory neuron remember that our sensory neuron is our afferent pathway that is going to be in blue so your Century afferent neurons conduct impulses from sensory receptors in the skin visceral or muscle to the central nervous system right so we're going through our afferent Century neurons and we're going to end up within our CNS most cell bodies are in the ganglia in the pns so here we have our ganglia okay and we're talking about the pns remember that the pns is not the same okay as your C and S your pns is going to involve fibers right so your motor efferent neurons basically transmit impulses from the CNS which is going to consist of your sprainers by spinal cord okay to the factors in the body so your inner neurons Association neurons complete the communication pathway between Sentry and motor neurons and their cell bodies reside within the CNS as we see right here right so when we break down this image it's not confusing at all because this is the stuff that we've already gone over now your structural classification of a neuron is based on the number of processes right so that's including dendrites and axons extending from the cell body if there are several the neuron is a multi excuse me a multi-polar neuron right because we have many dendrites right we only have one axon body though okay now a multi-polar neuron consists of many extensions from the cell body all motor and interneurons are multi-polar and are the most structural type that you're going to see so we also have bipolar neurons right so these are going to be bipolar neurons so neurons with two processes meaning one axon and one dendrite are bipolar neurons so what do we have we have an axon okay but we're going to have those dendrites and here we have the cell body now bipolar neurons are found only in some special sense organs such as your eyes and your nose where they act as sensory processing um basically as receptor cells and these are rare in adults now we have uni polar neurons okay and these are look a little bit different right because here we have the cell body okay here we have the dendrites okay and we have a short single process an axon okay and so basically your unipolar neurons have a single process emerging from the cell body as if the cell body were in a cul-de-sac of the make road that is the axon okay so they have a short single process leaving the samwadi as we mentioned before and your Sensory neurons are found in pns ganglia and unipolar neurons conduct impulses both towards and away from the cell body now neurons have two major functional properties irritability and conductivity right irritability is ability to respond to a stimulus by producing a nerve impulse conductivity is the ability to transmit the impulse to other neurons such as muscles and glands now Mr Warren has spinal cord damage that prevents nerve impulses from being carried from the CNS to muscles or glands what specific type of neuron has been damaged you guys should have all chosen the motor neuron right because remember receiving it is not the problem it's the efferent pathway that is damaged right so let's start talking about Action potentials okay so there are many different types of stimuli that excite neurons to become active and generate an impulse for example light excites the eye receptors sound excites some of the Year receptors and pressure excites some cutaneous receptors of the skin however most neurons in the body are excited by neurotransmitter chemicals that are released by other neurons so a number of factors can impair the conduction of impulses right so for example sedatives and anesthetics basically block nerve fibers by altering membrane permeability to ions right that's why some of you guys take Midol uh Tylenol ibuprofen and so forth right and so it's basically mainly affecting those sodium ions so no sodium entry means no action potentials so what happens just for next for an example just before we start talking about Action potentials and I highly recommend that if you have not seen the video that the supplemental video that I have provided for you guys I highly recommend that you view it first before you dive into this video about Action potentials right but basically just so you can have a better understanding right what happens when you sit on your foot for too long it basically goes numb just how my foot is right now right The Continuous pressure basically that I'm putting on my on my leg right around my foot is hindering the impulse conduction okay and because of this there is no blood circulation to the neurons right so when you remove or when I remove the pressure from my foot the impulse begins to be transmitted again leading to that unpleasant prickly feeling that you feel in your feet right and it tends it doesn't go away for a while so let's start talking about Action potentials so how would we achieve an action potential right how would we achieve this with sodium and potassium pumps and the resting membrane potential what is all that what are we talking about right so let's imagine that you have your neuron and it is capable of sending an Impulse to a receiving neuron and that neuron will decide if it's going to carry the signal forward or not right or if it just stops there the decision to carry something forward is an action potential okay so how does a membrane of our neurons make this decision in order to carry out that action potential so our membrane of the neuron at rest is going to have a lot of sodium ions outside of the membrane okay so basically what I'm going to draw here is the inside of the cell this is the anthite I'm just going to write it like that and this is the outside okay so on the outside of the cell okay we are going to have a lot a lot of sodium ions right so an a an a oh sorry guys and a a i okay and so in the inside of the membrane we are going to have potassium ions we're not going to have as many but we're still going to have potassium ions inside the cell okay so this means that the outside is going to have a net positive charge okay so we're going to have a net positive charge on the outside okay so it is going to be much more positive on the outside of the membrane that it is on the inside of the membrane right and in the inside it is actually going to be kind of negative so it's going to have kind of a negative charge why because we have less potassium then we do have sodium on the outside of the cell Okay so so at rest we have more sodium ions on the outside and more potassium ions in the inside and we are going to have a charge of about negative 77 millivolts at our membrane so this is going to be equivalent to 77 millivolts okay this is going to be at resting so our membrane potential is going to be the change in electrical chemical charge across our membrane so now our sodium and potassium ions do not remain the same meaning there are channels that are present inside of the membrane that allow for things like sodium to come in or for potassium to go out right so you guys learned this back in 1306. we have little channels that are located within the cell okay within the plasma membrane and these channels are going to allow for sodium to come inside of the cell and it's also going to allow for potassium to go outside of the cell Okay so when we have trouble these different ions across the membrane it will change the chart right so when we start crossing over this potassium or start crossing over the sodium this negative 77 is going to start changing right we're going to start getting more of a positive charge if we start having more sodium ions come inside of the cell so achieving a resting membrane potential is to have a bulk of sodiums on the outside of the cell and just a few potassium inside of the cell to give us a mostly negative inside the cell when we are resting membrane potential okay so this is that resting membrane potential that you guys see here now someone resting membrane potential sorry about my writing guys it's a little bit hard to do it on the trackpad okay so there are some ion channels that will remain open that allow some sodium ions in and potassium ions out just passively okay you guys learned this back in 1306. but there are other channels that we all that we call voltage voltage dependent okay and so voltage dependent means that they depend on a change in charge when we talk about the change in charge we're talking about the change that we see up here right so they are waiting on some kind of stimulus to come from another neuron so usually the stimuli are going to come in in the form of a kind of ion in order to stimulate okay so the stimulus comes in some form of of an ion and it is going to change the charge of our membrane and as it changes the charge it is going to cause our voltage depending gates to open okay so we are going to have our voltage dependent channels basically open and that is what is going to lead us to number two so that is how we're we are leaving resting membrane potential so it's going to be through a stimulus and it's because of those voltage-dependent channels and the stimulus is going to be in the form of an ion Okay so how do why do we get the stimulus and why do we get this change because of the voltage dependent open channels I'm going to leave it like that guys Okay so now imagine we are going to have some channels opening up and it's going to allow for a lot of our ions to come across so things like our sodium channels will also open up and as they open up our and as our sodium channels open up what do you think is going to be entering sodium right and if we start allowing sodium to enter into the cell what do you think is going to change are millivolts right and so basically what is going to end up happening is that the inside of the cell okay is because is going to become more positive and when we say that it is going to become more positive it is going to change from negative 77 millivolts okay to negative 55 millivolts okay so all that means is that it is going the inside of the cell becomes more positive because of our voltage-dependent channels that have become open Okay so more positive and also because it's becoming more positive it is going to be reaching something known as something known as a threshold and because it's becoming more positive we are no longer at 77 millivolts we are now at negative 55 millivolts because of uh because of that sodium that is rushing into the cell right so the cell is becoming a little bit more positive so we are going to reach a particular charge as I mentioned before negative 55 millivolts and this is going to be known as your thresholds okay at threshold this means we are moving forward with an action potential because we have reached a baseline charge that tells us we are going to shoot for it and we're going to go ahead and just move forward with that action potential as we reach threshold this will trigger something called depolarization [Music] so depolarization happens when our cell is undergoing basically a shift an electrical charge remember we went from negative 77 to negative 55 and it's going to result in a more positive cell inside and it will be less negative inside right so we are changing the charge so what are we doing during polarization we're conducting a change right because we're going to something more positive so A change is going to be something more positive okay and that means that we are going to have more sodium entering into the cell okay so remember it's entering inside of the cell on this side okay and so this all began when we reach threshold okay so more ions are basically coming in it is a More Voltage dependent Channel start opening as they open we will get an influx of sodium ions we can also open some of our potassium channels that eventually are going to end up meeting something known as a peak within the signal and now it will be extremely positive inside of the cell okay now as we come down from the peak it takes some time for the charge dependent basically voltage dependent to close up again and because of this it will keep the positive charge for a little bit okay so basically we'll reach a Peak at depolarization okay so we'll put Peak here okay so now we need to come down from being so positive right so that is going to be our repolarization so that's number four re polarization so what repolarization just means is we're going back to negative inside of the cell okay so repolarization means we have reached a peak and now we are slowly needing to come down from being so positive right so we are going to start the we are going to start to re-establish a negative charge inside of the cell so we will be working on our sodium potassium pumps in order to re-establish this negative charge our our cell will establish basically resting membrane potential okay so our last one which is our fifth one is going to be that we have gone back to normal right we have reached the beginning right where we were at once before so we're at the resting membrane resting membrane all right potential okay so when we reach resting uh re-establish resting membrane potential guess what we have gone back to 77 millivolts inside of the cell right so our cell is now negative again inside of the cell so it does basically us when we go back to re-establish re-establishing that resting membrane potential it's going to do this by having sodium and potassium ions going in and out of the cell until it gets back to that negative 77 millivolts that we have for resting membrane potential so I hope all this makes sense I know it's a lot of information being thrown at you so as we move through our sodium and I so let's just do a little recap for you guys right just you guys can basically understand this a little bit more so after you guys having all this information right so as we move through our sodium ions and our potassium ions when we get that stimulus and reach Threshold at negative 55 millivolts then we have made our cell a little bit more positive insight and once we reach that threshold this is like basically a baseline where it's basically stating we're going to go for that action potential like we're gonna move forward with this action potential so when that happens we are going to open up more sodium pumps more potassium pumps and it will cause our cell to become even more positive in the inside and basically reach a peak right and so when that happens then we are going to have the neurotransmitters moving into our synaptic cleft which we learned a little while ago right and they're going to have the neuron fire basically like little shots um and inspiring what's happening right it's what's going on and the neuron once it's being fired it's going to end up reaching its peak and then we need to come back down okay and that is when repolarization happens so we are going to go back to negative and this is done by closing Sony by closing the sodium and potassium channels that are charge dependent basically voltage dependent and when that happens sodium sodium leave the cell potassium goes inside of the cell until it gets back to its resting membrane potential to negative 77 millivolts so what cells form the myelin sheaths around nerve fibers within the pns all of you guys should have said Swan cells so now let's get back to what neurons do okay so reflexes reflexes are rapid predictable and involuntary responses to the stimuli they occur over occur over neural Pathways called reflex arches and they involve both CNS and pns your reflex arches are a direct route for from a sensory neuron to an interneuron to an effector now there are two types of reflexes somatic reflexes and autonomic reflexes somatic reflexes are reflexes that stimulate the skeletal muscle right so they're involuntary pulling your hand away from a hot object is one of those somatic reflexes autonomic reflexes regulate the activity of smooth muscles the heart and glands right so basically secretion of saliva we don't tell our mouth to secrete saliva right changes with an eye pupils we don't tell or our pupils to change right as far as getting bigger and smaller digestion blood pressure and sweating right this is all stuff that just happens voluntarily so there are five basic elements of a reflex Arch and they are as follows one we have a sensory receptor that reacts to a stimulus two we have a sensory neuron that carries messages to the integration Center three we have your integration Center which basically processes the information and directs motor output four we have your motor neuron which carries messages to an effector and five we have an effector organ and it's the muscle organ that is going to be stimulated right so it's this picture that you guys see right here so one we have the receptor right it's within on the skin you have a nail that comes and basically breaks the epidermis of your skin okay so what is that going to have it's going to have an afferent okay so we have your sensory neuron that is going to send that signal okay to your integration Center within your CNS where your spinal cord and your brain are located okay and so basically what we have and it is an interneuron okay that interneuron is then going to go ahead that integration Center is going to go ahead and say hey you know what we need to something needs to happen so basically that motor neuron which is your efferent pathway is going to send a signal okay to either your muscle or your gland and it's going to have any an effect right now we have reflex arches such as a two neuron reflex Arch and a three neuron reflex Arch okay and so a two neuron reflex are are very simple okay and one of the examples is your patellar right which is basically a knee-jerk reflex remember that your patellar is going to be your kneecap right and so some of you guys when you guys will get physicals for yourselves or your kids you guys go to the doctor and the doctor will get something and just go ahead and hit your kneecap okay when he hits your kneecap okay there is that's one that's going to be a sensory receptor okay that Century receptor is going to send the signal through your Affair and pathway okay into your integration Center okay and basically there is going to be a response so that motor neuron which is your efferent pathway is going to send an effector write an effect that's basically going to stimulate your muscle or your leg to jerk right right so it's going to be a teenager your knee is going to rise up all of us are doing this right now as we're sitting down and viewing this lecture or me talking about it because I am definitely doing it so most reflexes are much more complex than the two neuron reflex and it involves synapses between one or more interneurons within the CNS right and remember that your that's located within your integration uh center right so basically here we have your interneuron remember that your interneuron is going to consist of your synapses right and we talked about those in previous slides okay and so basically what we have is one neuron here and here we have a second neuron here okay so this is going to be known as number three as your interneuron so basically what ends up happening is we still have that receptor right your hand touches or gets poked by a needle okay then we have your Center receptor that is going to send it through your Sentry neuron which is your A-frame pathway it is going to enter into your CNS where your brain and spinal cord are located okay and your interneuron is going to be a not what's going to be responsible but basically um what ends up happening is it's going to say hey there needs to be a motor effort like an effect okay so your interneuron is going to take that through the synapse in order to go through the second neuron okay your motor neuron known as your efferent pathway is going to take that stimulus okay and it is going to end up reaching a muscle within for this example okay and basically your hand is going to jerk up or basically you're going to withdraw your hand okay so that is going to be it for chapter seven part one okay please look out for chapter seven part two