Transcript for:
Nervous System Overview

this is the first lecture for nervous system this is chapter 12 in your book which is nervous tissue and in this lecture we'll be going over the general functions of the nervous system kind of general characteristics how it's organized um different parts of the nervous system and then the bulk of this lecture we'll be we'll be talking about nervous tissue nervous tissue consists of neurons also we'll talk about neurons the characteristics their structure how we classify them both structurally and functionally um and then we'll actually talk about the difference between neurons and nerves and the structure of nerves we'll talk about what a synapse is and um Define two types of synapses and then we'll talk about the other cells that make up nervous tissue which are the cell all these cells that support neurons right we call the gal cells and going to talk about their characteris iscs their types where they're found either in the central or in the peripheral nervous system and then finally we'll talk about myelination what is myelination and why is it related to gleo cells so after the and your learning objectives for this will list and explain the function of the nervous system demonstrate how the nervous system is organized label the parts of neurons be able to draw them out and ident understand the function classify the neurons based upon both structure and function we'll go through the structure of a nerve we'll go through what a synapse is and how to determine what electrical versus chemical synapses are go through the different types of gleo cells and then finally understand the role of myelination and how the myin sheath is created in neurons all right first the overall nervous system all right the functions of the nervous system it is your communication and control system it collects and interprets information right from the outside so it it it detects stimuli right so it detects stimuli and then um we take in information from the outside stimuli uh what how warm it is touch receptors um Etc so that information right that is collecting that is what we call an aarant pathway or a sensory pathway right it's a information is coming into the system right and then we have the the processing and evaluation of of that information right this is the control center part the interpretation portion of of the nervous system right it is we're going to interpret what that stimulus is and if there needs to be some type of response by the body or by the by the organism right to determine what that response is and to initiate that response right so then the response is what we call the eer pathway okay eant is also mainly a motor pathway all right so motor output okay and sensory input right two different systems or two different portions of the whole system of the nervous system so it collects information interprets that information determines the appropriate response and then initiates that response to the affectors either muscles or glands all right so that's the struct that's the functions of the nervous system like to collect information interpret that information and then determine the response all right organiz ation Al we can break the the the nervous system down into either the central or the peripheral right the central nervous system or the CNS is comprised of the brain okay the brain is your main control center where we interpret information most of our sensory information comes into there and it's interpreted somehow all right our brain is where our higher order functions are right personality reasoning logic um motor output sensory information is is interpreted Etc right the spinal cord right runs up the vertebral canal and that is also part of the central nervous system right and the spinal cord initiates and and moves relays information to and from the brain from all of the exterior Parts okay the peripheral nervous system or pns all right is consist consists of all the nerves all right which are fiber bundles right so they're neurons that run through the from the spinal cord out through these nerves to the peripheral points of the body right and those nerves can either be sensory or motor and we'll talk about those in in in general or they could be a mixture of both right but so nerves extend off of either the spinal cord or the brain and they go out they relay information out to the different parts of the body and then ganglia right is a collection of cell bodies along the nerves right so um a ganglia or a ganglion singular ganglion is a singular is a collection of cell bodies and a cell body is a part of a neuron all right that makes up a the structural like the beginning part of the neuron and then so you have have clusters of ganglia are basically clusters of Parts the originating parts of a neuron and then from that originating part or the cell body extends an axon which will relay the information from the ganglia out to parts of the body right so it'll go so here's a ganglia and it'll go out to let's say internal organs or it might go uh from the spinal cord when you have a ganglia that goes out to the arm or whatever distal parts of the body body we're talking about so structurally Central versus peripheral functionally little different right so functionally we have sensory nervous system or the aeren pathway which brings in sensory information so it receives sensory information like we already just discussed from receptors and transmits it brings it into the central nervous system all right or we could have the motor nervous system which is the eant outgoing so output mean the signal is going to rise from the central nervous system and be sent out to uh affector organs muscles right or glands and each of those we can break into two different parts we we call a somat a somatic sensory system somatic refers to conscious understanding right so somatic sensory detects stimuli we consciously perceive Steve right you're listening to my voice you are looking at the video um those are conscious stimuli that you're receiving as opposed to visceral sensory information this is stuff that you don't consciously perceive right so we typically don't understand right signals from the heart or the kidney right changes in blood pressure we don't really think about or understand like that's happening in the body or changes in blood glucose or whatever internal change happens that we don't consciously perceive as a change right but our visceral sensory system detects that and change relays that information and then the appropriate response is mitigated so just like we have somatic and uh in sematic and visceral in the sensory nervous system we have somatic and visceral in the motor nervous system so our somatic motor um system right sends voluntary signals to skeletal muscles right so motor neurons again somatic means conscious conscious control somatics when this curse in case voluntary conscious control our visceral motor system or also known also known as our visceral motor as our autonomic motor system sends involuntary commands to Heart smooth muscle and glands right and that's more commonly referred to as you we know there's two branches of the autonomic nervous system the sympathetic and the parasympathetic and your sympathetic is your fight or flight responses and your parasympathetic is your rest and digest responses and we'll talk more about those branches um in a later lecture um on the autonomic nervous system and what happens um in that um responses so sensory and motor both and then both somatic and viseral um portions of each of those functional organizations all right and so here's a picture kind of our flowchart is showing you the same thing central nervous system peripheral nervous system and really the peripheral is broken into sensory and motor sensory information right AER pathway come from sense organs this also could be receptors whatever sensory information comes in okay um and that could also be um both sensor visceral right from sense organs intern internally let's say from the heart or the lungs right stuff we don't perceive or or um somatic which is stuff we do distinguish um understand and perceive as stimuli like looking at light hearing sounds touch receptors all of that sensory information your motor or eer pathway right so it's going to carry informations information from the central nervous system peripheral nervous system out to affector glands and organs right and we have both a sematic branch which is your voluntary to skeletal muscles or the visceral the involuntary um branch which goes to cardiac smooth muscle and glands and the two arms of that system both parasympathetic and sympathetic and again we'll talk more about that that um in a later chapter all right so here's kind of the breakdown for another picture same thing functional organization sensory versus uh versus motor or or sensory aent sensory is AER motor is eer so incoming messages on the sensory outgoing messages on the motor and you have both somatic and visceral um sensory somatic and uh autonomic motor or visceral motor that you know those are almost synonymous and you can see we kind of they're targeting different tissues right so both of those pictures help to explain kind of the different functional organization of the nervous system structural organization is Central versus peripheral functional organization sensory versus motor and each branch of the sensory and the the somatic and the visceral of each of those branches in general okay so let's talk about now we talked about the general characteristics of of the whole system let's talk about the structure of neurons or or the characteristics of neurons because neurons are the functional cells of the nervous system right so nervous tissue is made up of neurons and all the cells that support neurons so neurons are the the the functionally the more important cell right so neurons are going to transmit your messages okay the impulses transmit messages we'll put impulses okay either either both either sensory right or motor information and you'll see there's there's actually a Third Kind we'll talk about that in a little bit all right but neurons in general have certain characteristics similar to what muscles have okay so neurons in general they are excitable okay that means that they can respond to stimulus similar to what a muscle was right the stimulus can cause a change in the cell's membrane potential you're able to recognize a the presence of a a chemical or an electrical impulse and the the neuron is going to respond to that in some way second is that the neurons are conductive they neurons are have the ability to propagate an electrical signal right they can generate an action potential and that's related to voltage gated channels along the membrane open and close sequentially propagating a change in the membrane potential down the axon of the neuron neurons also exhibit the ability to secrete or secretion all right at the axon Terminus if you recall from M our muscle cells at the axon Terminus something is released from a motor neuron that goes across the synapse and binds to the muscle cell that something is a neurotransmitter in the case of muscles that neurotransmitter was acetylcholine okay so Nur neurons have the ability to stimul uh synthesize and release neurotransmitters in response to those impulses and the conductive activity in general all right neurons also exhibit extreme longevity right they're not really for the most part they're not mitotic all right they basically you're mostly you are born with all of the neurons you'll ever have all right and they die from there so they can live very long right and they are atic meaning that they after fetal development they do not grow in most neurons they don't undergo mitosis they don't replicate so you have the neurons you're you are born with and if they are they are damaged or die for some reason they are lost right they not getting them back all right so let's talk about parts of the neuron General structure I'm just going to run through the parts and then we'll draw it out on on another slide um all neurons have a cell body which which is the main part is also called the Soma and that contains your your nucleus and then there all these other thing we call these um smaller structures called nissle bodies right nissle bodies are what we call chro chromatophilic substance there's nissle bodies have ribosomes and so when you stain a neuron um there's some darker spots and darker areas of the cell body right around the nucleus that are made up of ribosomes for the production of proteins and and neurotransmitters Etc that are necessary for the function of the neuron so the cell body is like the biggest portion of the neuron um and it also off of the cell body are then extensions right and so we have two basic types of extension extensions from the cell body dendrites which are which are short unmarinated processes Branch off the cell body and their job is to receive input and transfer it to the cell body which then can determine or recognize if there's a signal necessary to be to a stimulus to respond to right and then what that response is it can then um mitigate that response in general okay and then the second extension is what we call the axon the axon is the longer process emanating from the cell body and it makes contact with other neurons muscle cells and glands um it attaches to the cell body we call the axon hiloc and it has axoplasm and there are axon collaterals which are can be branches um and then you have the the end points the axon termin which are important right the axon terminals where you'll have have the these are called t tendria and you have the synaptic knobs or the the terminal buttons which store synaptic vesicles containing your neurotransmitter right and it's the function of the axon is to conduct the message away from the cell body so let's draw and just kind of label a neuron real quick right so the cell body is the main portion I like to draw it kind of like U kind like this right so I will draw a cell body and this is kind of the the typical structure of a neuron right so there's your cell body with a with a nucleus and around the nucleus you may have right these nissle bodies darker staining areas right so that's your nucleus these are your nissle B IES or chromophilic substances chromatophilic substance okay um this whole thing and I'll do it like this is the Soma or the cell body okay each one of these extensions are your dendrites and they are going to carry message into the cell body all right so those are your main extensions off the shorter extensions off of the cell body then there's always one longer extension off the cell body which is your axon itself so this is the axon right here's your axon Terminus that's where the synaptic vesicles will be found this this area actually I'll I'll just highlight it here in yellow right this area is the axon hillock all right and so that's kind of the main structure of a cell body now the the the axon is is can also be a melinated axon all right so a melinated axxon have um these milin sheets that wrap around the axon itself all right so let's say this so that's the myin sheath and then in between each of these axons the space in between are what we call your neuro fibral nodes also called the nodes of ran right so the the milin sheath isn't a continuous sheet they actually broken up in different areas and there are openings um within the sheet kind of spaces that the um axon can be accessed to right kind of exposed right so basically that's the structure of a the general structure of a neuron and for your understanding purposes this is a multi-polar neuron and it's multipolar because it has multiple extensions coming off of the the cell body it has lots of dendrites and one extension of the axon all right um your text also talked about axon collaterals right so in some cases this axon can Branch imagine it having another Branch uh so it has a collateral it's still one neuron it just has multiple branches at the Axel at the end of the Axel um the neuron itself has lots of uh has a cytoskeleton like most of other other cells the the cytoskelet are made up of microfilaments intermediate filaments and microtubules um and they are important for providing strength and they also provide a pathway for movement of materials all right so your the nuron cell will utilize the cytoskeleton kind of like a as a as a ra a railway to move materials down like a train track to move you know throughout move materials throughout the body throughout the cell itself all right so here's a picture of a typical neuron right all the things we just talked about the peric Carion is the same thing as a cell body um these are your dendrites shorter extensions right Chromo chromatophilic substance which is a nissle body there's a nucleus there's also a dark nucleolus that's present on typically in the nucleus you be able to see the axon H hilock is that triangular region where you have the axon extend from right the axolemma is the cell membrane of um part of the cell membrane over the axon so we have talk about axolemma or neurolemma the neurolemma is the cell membrane of the of the neuron the axolemma is the PO part of that um cell membrane that extensions extends over the axon so here's the axon and the showing you your milin sheath right the milin sheath is composed of different types of cells depending on where in the in the nervous system you're looking at this neuron if it's in the brain that M sheath is produced by oligodendrocytes we'll talk about those in in a little bit and if it's in the peripheral nervous system then this Mile and sheath is made up of um we call neurolemmocytes or there's your neurolite or Schwan cell all right and then at the the end of the axon we have the tendras right the end points the axon termin and in this case this axon Termini multiple ax multiple um tendra on the the target neuron and then you have your synaptic vesicles that are present in the axon Terminus right which will release neurotransmitter into the opening between that and its Target cell to elicit elicit a response and the top right panel here this is the P histological picture of your neuron showing your chromatic substance right this whole cell body whole cell body nucleus cell body these are all dendrites right here's your axon hilock and the axon itself now neurons have to synthesize and move material to and from different parts of the neuron especially down the axis right and the axon can be um inches feet away from where the cell body is so there's a lot of different movement of material to and from the cell body all right so that that transport of material can be two one of two ways it could be anterograde means it goes from the cell body towards the synaptic knobs right so from the cell body to the synaptic knob that's anterograde okay retrograde goes goes back to the cell body right from from the axon back to the cell body retrograde is back to where it came okay and this can occur by we call fast AAL transport or slow axonal transport fast and slow are basically dependent upon how the transport occurs does It Go by diffusion that's going to take some time so that could be that's probably slow transport or does it utilize the cytoskeleton and utilize ATP that's going to happen much faster okay so fast accidental transport involves moving along the the microtubules all right so utilizing the cytoskeleton and utilizing ATP right and fast transport can be both ways right an anterograde or retrograde okay and that's just utilizing ATP and moving the moving things along the rail system of the cytoskeleton slow external transport right is mainly it results from flow of axoplasm the cytoplasm inside the axon all right and that happens more like a diffusion or kind of like sitting imagine floating on on the ocean and you're just at the mercy of the current the the current is going just kind of like pull you away that's going to happen much slower than if you were um had a motor on on a boat right that right that's going to happen much faster so that's the difference between slow and and fast axonal transport and again both of those can happen in both uh Antero or retrograde so now that we understand the the structure of neurons we can classify neurons based upon their structure okay and the structure is basically one of of four different types and the structure we classify neurons based upon the number of processes that are coming off the cell body all right so we have both multi we have multipolar many dandrites one axon and that would look something um like this right so nucleus here's your cell body dendrites and then you would have one [Music] axon okay but all of these dendrites are present one axon one long axon and axon Terminus that's a multipolar neuron okay a bipolar neuron has one dendrite and one Soma right and extend from the so so one sorry one dendrite and one axon extend from the Soma so here's the so here's the Soma here's the nucleus right and then we have one dendrite and we have one axon so really we have two extensions off of the cell body okay and so what you have there is a bipolar two extensions right two one two extensions off the cell po off the cell bottom unipolar neurons a little bit different okay okay they have a nucleus and we have a cell body but uni means one so we have one extension that is then split into two different parts okay but you have one axon that ex one extension that goes from there and then it splits into two parts okay and one's a peripheral process one's a central process all right and this is splits into several receptive gend typically um kind of goes right from a dendrite to the axon Terminus and then you have an axonic neurons that have dendrites but no axons so that would look something like this cell body right and you have all these dendrites but none of them are axonic there's no axon right and that's a TP that's a little bit different their job is kind of of to re to relay messages from one neuron to another so four different types based upon structurally classified neurons based upon how many processes come off the cell body right and here are your different ones right so multipolar lots of dendrites one axon bipolar one dendrite one axon unipolar one axon but two parts to that axon and then an axonic only dendr are present right there's not one longer extension of the axle so structurally we can classify neurons we can also functionally classify neurons and the functional classification is just based upon where are they where are the message messages that they're transmitting going where's their destination right so sensory in Sensory neurons or AER neurons are going to carry conduct input from some itic and viscal receptors to the central nervous system right we're going to the the CNS from the outside to the central nervous system most of these are unipolar some are bipolar right things like bipolar ones are like the the sensor the uh neurons that are in the uh sensory receptors in the eye right they recognize intensity of light that message is sent to the brain right that that's a bipolar neuron but a lot of these Sensory neurons are actually unipolar second functional classification are motor neurons or eer neurons they conduct output from the central nervous system two somatic and visceral receptors right such as like uh somatic would be skeletal muscles visceral would be like heart uh organs like the stomach intestine right and glands right like endocrine glands all of these motor neurons are multipolar and then finally we have associate inter neurons or Association neurons they can receive proc process and their big function is integrate information from many other neurons so they will communicate between sensory and motor pth Pathways all right so they're so the inter if you think about inter inter means between right so they their communication between one neuron and another right and they're located within the central nervous system and they actually make up most of our neurons all right and generally all are multipolar most neurons in the body are multipolar in structure right and most most of them are interneurons by function so here's sensory input skin receptors this is a sensory neuron goes through one pathway through the cell body of that is present here this is a structurally that is a unipolar neuron right sensory information brings it into the spinal cord where it terminates on an inter neuron so your sensory neuron and Inter neuron which is going to integrate that information um and relay it to a motor neuron which is multipolar right and extends that out to motor output so here you have both you have a um a unipolar neuron and two multipolar neurons but functionally you're all the difference right we don't have a bipolar neuron here or even an anaxonic neuron now neurons are bundled into a structure called nerves nerves are mostly a mixture of both sensory and motor neurons right so they'll carry AC messages in and out all right and so you have all of these parallel axons that are you know they're going in the same direction they are bundled in the structure of a nerve and the nerve is structured very similar to what we had in muscles right in muscles we had the skeleton muscle cells were bundled into a faasle right the skeletal muscle cell itself was bundled and covered by the endo myum and then those skeletal muscle cells were bundled into a fasle the fasle was covered by an endo excuse me a per mum then the whole skeletal muscle had multiple faical bundled together and covered by an epim mum similar thing happens in neurons right in this case we have an epineurium which closes en closes the entire nerve underneath that epineurium the axons are bundled into different fases right and each of the faasle is wrapped by a per nuum right and then within the perin nuum or within the fasle are multiple axons that are covered by the endon nuum all right and this is what it looks like so here the whole nerve is covered by the eperium each of these is a fasle right they can be different sizes all right with the fasle Bund which have bundles of axons the fasal are covered by the perin nuum and then inside the fasle are separate axons and the axons are covered by the endon nuum which encloses the myin sheath and the axon as well think of it as a way of um insulating one axon from another all right but we also bundle all of the axons into a single nerve for Comm Comm unication make ease of communication right and everything's kind of in one area and here is a scanning electron micrograph of a neuron right showing your your the the the faasle itself right in the Peruan that covers a faasle this whole thing would be covered by the epin nuum and each of these axons is covered by the endon nuum within the fascal itself and the the axon then ends up being little the little uh um dot in the middle of these um circles now you'll notice that some of these are are white and some have like a white circle surrounding the middle part that white circle is the milin sheath of uh of the axon so how do we relate neurons to nerves right so nerves are made up of lots and lots of axons from different neurons and we can classify nerves based upon where they originate from structurally you they come from they originate from the brain which are cranial nerves and there are 12 cranial nerves all right or they can extend from the spinal cord and you have 31 spinal nerves all right so really cranial nerves from the brain spinal nerves from the from the spinal cord that's structural classification of nerves now functionally it's a little bit different right either a nerve can be sensory where it carries information into the central nervous system only sensory information it could be motor which carries motor information away from the central ner nervous system or it could be mixed right and those mixed can have both sensory and motor neurons so that's kind of like a two-lane road that's present right because information can go be can be relayed into the central nervous system or away from the central nervous system for those mixed nerves right but individual neurons within that nerve only carry information One Direction so do not get that to do not get that um mixed up right a nerve can be can carry mixed information because it's made up of lots and lots of neurons but each singular neuron within the nerve can only carry either sensory or motor information because there's no two-way street on a neuron only on a nerve now at the end of a neuron are what we call a synapse and we talked about this in in the muscle chapter right a synaptic Clift or synapse is a separation between the neuron space where one neuron ends and the next neuron or muscle or gland begin all right so that's what the synapse is it is a separation between a muscle or excuse me the end of one neuron and the beginning of another cell all right and there are two types of synapses chemical and electrical and chemical synapses are more far more common than electrical synapses and they are they are synapses that utilize right these utilize a neurotransmitter so for the most part we're going to be talking about those right so think about acetylcholine crossing the synaptic left from neur motor neuron to muscle cell okay and for the most part most of the the synapses in the body are chemical synapses however there are some electrical synapses and so an electrical synapse involves your PR PR synaptic and post synaptic neurons what does that mean right so let's say here's the axon of one neuron and it terminates here and then the next neuron is the dendrite of the next neuron starts right there I'll just kind of go like this in terms making this a a uni neuron there's no space in this case between the we call a pre pre synaptic means before the synapse and post synaptic neuron right so post is after the synapse okay in this case the there the two neurons are held together by Gap Junctions which allows the impulse to be carried down and propagate directly into the next neuron all right so there's no synaptic delay there's no release of neurotransmitter the neurotransmitter doesn't have to uh diffuse across the across that synapse and bind to its receptor right it just the ions and the electrical impulse directly are um transferred from one neuron to another so your chemical synapse your press synaptic neuron right so here's your press synaptic neuron with the axon Terminus and your post adaptic neuron we'll call this a little multipolar one right there's a a a space between here we're going to release neurotransmitter that has to go across cross the synapse bind to the dendrite or the neuron or gland and then that message can be relayed from one to another all right now in this case all right and so that you have a synaptic delay all of the events that happen from release of neurotransmitter diffusion across the synaps and then binding to the receptor on the neuron or on the target cell takes a little bit of time that time is the synaptic DeLay So that covers kind of the characteristics of neurons we'll get more into how neurons function in terms of generating action potential in a later lecture for now let's talk talk more now about um the cells that support neurons or what we call neurog Gia right or gal cells right the so these nervous tissue cells are not excitable they do not they don't carry impulses but their job is to support the cells found in the Central and peripheral nervous system they're mainly there to support neurons and protect neurons right so they really protect and nourish neurons these cells are capable of mitosis they are smaller than neurons but they are more numerous they they can uh they do not relay messages they're not excitable however they are capable of M of mitosis okay and they are critical for the normal function at neural synapsis and the noral the normal function of many neurons in general there are six types of gal cells okay four of them will be found in the central nervous system okay and then two will be found two types in the peripheral nervous system I want to talk about each of them all right so first gal cells of the C central nervous system are first one are astrocytes these are star-shaped cells um they kind of look like this all right they provide a very important function for the brain and for the uh the central nervous system in general right they help provide what's and form the blood brain barrier right their job is actually they wrap these feet around blood vessels all right so here's a blood vessel and those feet are wrapped around it and it prevents things from getting out of the brain out of the blood into the brain right so it it kind of selectively permeable it guards the gate the the aite guard the gate and the entry into the brain itself all right and they get help is very important because there are substances we do not want to get into the brain because they could be damaging to neurons right so things that can get in there include you know like plasma um some nourishment we want glucose to get in there things we don't want to get in there are like big um Pharmaceuticals right so drugs we don't want anything could harm neurons we don't want to get in there all right and so they regulate the tissue fluid composition around the neurons by absorbing potassium ions and help regulate its concentration and this is going to be very important this is going to be very important when we talk about an action potentials right think about all of the action potentials that have to be going on in your brain at one time and that's a lot of sodium and potassium that going to be moved you know into the cell out of the cell and if if too much potassium builds up outside of the cell then we can it might stop the repolarization of the neuron and can stop neurons from propagating producing Action potentials so these cells astrocytes can absorb pottassium and prevent potassium from ever like building up too much in outside of a of a neuron cell so it can always produce Action potentials okay and then another important activity is of asites is that they when neurons die Asos asites take over the space they fill in the space when a neuron's dead second type of gal cells are called endal cells and these are simple cuboidal EP or simple columnar epithelial cells that are found right they form What's called the choroid plexus they're found in the ventricles of the brain right their job is that they big job is that they help produce cerebral spinal fluid okay cerebral spinal fluid is liquid that kind of bathes and fills the cavities of the central nervous system it's found in the ventricles of the brain it washes over the brain kind of like where it's the fluid that the brain kind of floats in within in the skull it also cerebral CSF or cerebral spinal fluid also floats around the spinal cord and inside the middle of the spinal cord and helps protect that as well right so very important um material or or fluid that's Pres present in in the brain right and it's the choid plexus right is is the area where these endal cells are and they help produce cerebral spinal fluid um within the ventricles of the brain the next type of gal cell within the central nervous system is our microa these are fosic cells right these are your kind of waste management system of the nervous system right they removed debris and uh from damaged uh central nervous system tissue they also engulf infectious M agents that could find their way into the brain itself right so these are cells that help protect and remove wastes from the central nervous system the last type of central nervous system um gleo cell it are olend sites and oligodendrocytes are the cells that um they form the myin sheath around neurons and this is only in the central nervous system right so that's only in the brain and spinal cord so these cells will kind of have extensions that kind of wrap like hold on to and wrap around the axon Terminus of nearby neurons insulating them from each other all right and the purpose of the myin sheath is that that insulation allows for faster action potential conduction right faster action potential propagation so the impulse travels faster on a melinated axon as opposed to an unmated axon so here are the cells of the uh gal cells of the central nervous system right we have here right so here's the endal cells that line the centrical of the brain and they help produce cereal spinal fluid these green cells are your astrocytes they wrap around the blood vessels of the brain forming the blood brain barrier okay and you have a couple neurons these bluish ones are your micral cells these cells will break down all right they fagoo anything that's around right and break down remove any cellular debris from damaged or uh dead neurons and then finally these light blue ones are your olgod dender sites and you can see they have extensions that wrap around the axon of nearby neurons insulating them and allowing for faster conduction gal cells of the peripheral nervous system two types satellite cells and neurocytes all right satellite cells their job is that they are arranged around cell bodies in a ganglia right remember that a ganglia right is a collection or group of cell bodies of neurons right so we have all these cell bodies that are present right and kind of be like this here's a cell body all right and this maybe this is a dendrite cell body all these are present and they're grouped together but in this case there's no insulation between one cell body and another and so these satellite cells help protect kind of like insulate and separate one cell body from another one okay because there's no presence of a m and sheath around a cell body so we have to have some type of insulation to separate these two um separate cell bodies from each other you know electrically and then finally our last type of gal cell um are neural oyes all right neurocytes are also called Schwan cells um and they their job is that they um and sheath peripheral nervous system axons with myin right they per they and they produce the myelin sheath uh on peripheral nerves right so neurons within the peripheral nervous system are are the myin sheath is produced by Schwan cells and again M and sheath in general allows for faster action potential propagation due to what we're going to call saltatory conduction we'll talk about that um in a later lecture right but the the presence of the Mya sheath allows for uh saltatory conduction and that is a faster conduction of an action potential than if you if an axon wasn't an unmated a on all right so here's the two types of gal cells in the bral nervous system right here's your cell body and you can see that all this collection of cell bodies all close but they're they're separated from one another by these satellite cells and then you have the Aon that is wrapped by this neural lemoy wraps around grows part of the membrane and wraps it around the axon um and providing a milein sheath around the Axon clinically some of the things that are related to the central nervous system include uh tumors of the central nervous system right these sometimes occur in the central nervous system typically they're not um originate from neurons right remember that neurons are atic so typically it is a um a supporting cell that is is growing faster that um will or has uncontrolled growth that will cause a a a brain cancer or a nervous system Cancer all right those tissues with the capacity to undergo mitosis do that and they become they grow abnormally and then unprotected and then now they grow too much and then they start to form problems right and these are typically we call gomas right you might have something like an astroy that's a a grow a growth of the of the um astrocytes a gly blastoma is a Goma right it's a it's a gal cell tumor right and they can be malignant and they can be capable of metastasizing most can be relatively benign problem is that any any growth that happens inside the skull could cause um problems to nearby tissues right so maybe it's not not metastasizing or invading other tissues but probably putting too much pressure on other areas um and then causing um other problems with just kind of the general structure of the brain in general and where it is in the capacity of the skull we talked about myelination right is the process of wrapping an axon with myin right and there's several layers of membrane right so think about kind of what that milin is we have an axon I just kind of like this is the axon if we're looking down the axon and then around the axon are layers of myin of the membrane of the the neurolo site okay and then what you have and and then you have another one over here right those layers are extensions of the cell membrane of that Schwan cell that wraps around the axon many times so what you end up having is multiple layers of phospholipid bilayer surrounding the axon thereby insulating it from the nearby cells and then we talked about what neuro fibral nodes were and the nodes of ranir when we talked about the structure of neurons here's how that works right so we have neurol lemoy is grow and as it grows it's going to tuck over tuck under this membrane and continue to kind of grow from there eventually having lots and lots of layers of uh the uh cell membrane of the Swan cell that is insulating the axon underneath right and then same thing so here's your your milin sheath in the peripheral nervous system neurocytes right we talked about the neuro fibral nodes which is the separation between um where the the breaks in the myin sheath itself right and the central nervous system little bit different oligodendrocytes produce that and extensions of these cells uh of the Endo oligodendrocytes wrap around nearby axons they're the axons in the nous nervous system and the central nervous system are very close together so there's no ner leml formed but you have this um protection of the m and sheath as these um oligodendrocytes wrap around the axons in the ner in the central nervous system now UNM we not all axons are melinated we do have axons that exist in the peripheral and in the central nervous system that are unmated right so they're not associated with oligodendrocytes or they're not covered by a neurol lemoy right so in this case here showing you this neural lemoy Schwan cell is kind of starting to protect a couple of these you have multiple axons these are unmated right but it's separating out right so allows starts to develop envelop these things and that it kind of separates them in general right so a separation but we're not not really wrapped around completely around the axon these are unmated axons and then in central nervous system there's just not no association with oligodendrocytes in general major major clinical uh condition that's associated with um the myin sheath is multiple sclerosis multiple scler sclerosis is a progressive loss of the myin sheath in the neurons within the central nervous system this is an autoimmune disorder right what this means autoimmune is means that your immune system is recognizing something in your body that's should be there normally a normal body protein or body part of a cell or something but your immune Sy system is reacting to that as if it was not supposed to be there so it's actually those the in this case the oligodendrocytes that create the Ain sheath in the central nervous system are being attacked by immune cells and they're dying off therefore the there's a loss of the myin sheath in the central nervous system and so these repeated inflammatory events cause scarring right loss of of overall loss of the myin sheath and eventually can lead to permanent loss of function okay another clinical uh condition is Julian bar syndrome which is a loss of myin from P peripheral nerves due to inflammation all right so this could also be it's can be related to Multiple Sclerosis all right but when we're losing the myin sheath from peripheral nerves not send not nerves within or neurons within the central nervous system okay but Julian bar syndrome most function can be recorded recovered with um some medical information right but this is characteristics of some uh some muscle weakness in distal Limbs and um this can advance to proximal muscles in the limbs itself right so we don't want that to happen we want to control multiple sclerosis and prevent uh repeated inflammatory results or inflam FL we call flare ups because every sub every subsequent flare up is going to there's going to be loss and loss of more continued loss of more and more milin from the central nervous system neurons and then that's going to lead to a a further decrease in in overall function so in this lecture we went through the stru the organization of the nervous system both structurally and functionally the classification of different parts was like anatomy of the neuron uh and we classifi them both structurally and functionally um and kind of different parts either sematic uh or or or visceral right um and then we talked about them either sensory or motor and then we talked about different parts of the neuron um and went through the kind of the microanatomy of the neuron in general we also talk about the gleo cells uh six types of gal cells four in the central nervous system two in the peripheral nervous system and we went over what they do especially went through the structure and the importance of myin in the nervous system so that finishes nervous system lecture one