Transcript
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Introduces the six types of neuroglial cells in the CNS and PNS and details astrocyte structure and functions, including ion balance, neurotransmitter recycling, synapse support, and blood–brain barrier maintenance.
Speaker A
This is lecture 16, part E. So this is the last part, part of Lecture 16, PowerPoint, and we are going to talk about the supporting cells of nervous tissue, which are your neuroglia.Okay?So you have six different types of neuroglial cells in your nervous system.Four of them are found in this cns, so, so in the brain and the spinal cord, okay?And two of them are found in the pns, okay?
So found really within your spinal nerves or cranial nerves.Okay?And this image, you can see three of the six neuroglial cells.So they're.These guys right here are called astrocytes.
These guys are called microglia.And these guys right here are oligodendrocytes.So all three of these, along with other neuroglial cells known as ependymal cells, are found in this cns, okay?And two of them called Schwann cells, which are shown here, or these guys, these purple ones found around the cell body of this sensory neuron.These guys are called satellite cells.
So neuroglia are really, really abundant.They outnumber neurons, especially in the CNS, 10 to 1 or even more, and make up brain.Neuroglia, unlike neurons, can divide throughout life, okay?So they do undergo mitosis.And in fact, in fact, most brain tumors are due to glial cells dividing unchecked, the unchecked division of glial cells, so undergoing more mitosis than they should be.
Speaker B
So the four types of neuroglial cells
Speaker A
in your CNS are called astrocytes, microglia, ependymal cells, and oligodendrocytes.
Speaker B
So first we're going to talk about astrocytes.
Speaker A
They actually have quite a lot of functions.So the overall function for neuroglia is support.
But then each neuroglial cell has different types of functions.So these astrocytes, the first of all, they're the most abundant neoglial cell type.The reason they're called astrocytes is because they look like stars.Whenever you hear the term astral, that has something to do.
Whoever named them thought they looked like stars.So they have many cytoplasmic processes.So this is right here an astrocyte with its many processes that terminate in these little end feet, which, and these little end feed surround either neurons.So you can see this is an axon and an axon terminal of a neuron.So this astrocytes, these processes are, these end feed are surrounding the neuron here.
But then these guys are the, these end feet of this astrocyte.Same astrocyte is surrounding, attaching to brain capillaries.So you can also see that in this image here is a neuron and an axon or a dendrite, this, this purple guy here and here, that's supposed to be capillaries.
Speaker B
Right.
Speaker A
So your astrocytes surround both your neurons, but also surround at high levels your capillaries.
Okay.Now one of their function is functions, is to take up and release ions to control the environment around neurons.So we didn't really, when we talked about the action potential, we didn't really talk about the ionic environment.The environment, like what type of ions are found outside of the neuron and inside of the neuron.We briefly talked about those sodium ions, but we didn't really talk about calcium ions and, or potassium ions.Those are really, really important as well for neurotransmission.
Speaker B
Super important.
Speaker A
And they are discussed.Well, at least calcium ions are discussed in my PowerPoints, but we are not going to talk about them in this semester.But nonetheless, the environment, the ionic environment that's outside of the neuron plays a really, really important role in neurotransmission and, and the ability to generate action potentials or, or graded potential.
And astrocytes, one of their jobs is to kind of control the ionic environment by either taking up ions inside of them or releasing ions just to make sure that the, the environment outside of a neuron is just right.Okay.They also recycle or take up and recycle neurotransmitters.Okay.So those neurotransmitter, these little dots right here that are released by axon terminals of neurons, they don't stay around the synaptic cleft forever.Ok?Okay.In fact, you don't want them to be there.You want to be able to stop neurotransmission when you want to.
Speaker B
Right.
Speaker A
So you have to remove that neurotransmitter.And there's multiple ways to remove that neurotransmitter there.One way is to, you have enzymes here that can break down this, these neurotransmitter molecules.Another way to remove this neurotransmitter from the synaptic left is, is to take it back up into the neuron.
Speaker B
Okay.
Speaker A
And a third way is that that neurotransmitter can be taken up.You can see this arrow right here.So certain neurotransmitters, such as glutamate, can be taken up by astrocytes, converted into something known as glutamine.And then that glutamine is then brought back into the axon of this neuron so it can be reused again.
Another, some Other important functions is that they're really, they're very much involved in cell synapse formation, in developing neural tissue.So in utero as well as in childhood and, and adolescence, your neural tissue is developing and you're forming synapses, right?So you know, this right here, what is this?This is a synapse, right?So anytime an axon terminal, typically an axon terminal of a axon of a neuron, is close to and communicating with the dendrite or cell body of another neuron, that's considered a synapse.
And so a little bit about synapses.Now, the way you might wonder, like if, if we don't make more neurons, if we're, if our brains are in spinal cords, are not really great, good at making a lot of new neurons, which is something I already told you, right, that neurons don't undergo division, then how is it that we can learn, okay, and, and, and learn and memorize things?It's not because we're making more neurons, right, to store more information that way, but what we are making of and strengthening is synapses.So we can increase the number of connections between neurons, these synapses, okay?And also not only increase the number of them, but also strengthen the connection between them.
Now, this is much more complicated than that.We don't have the time to go into that.But just know that synapse formation, both in developing neural tissue as well as in, in adulthood as well, synapse formation is an, is an important thing.And astrocytes are involved in that.Now, astrocytes also are important in producing molecules that are necessary for neural growth when neurons are growing, when they're budding axons from cell bodies and their axons grow and make connections.
And finally, astrocytes are important in helping maintain and support cells, something that's known
Speaker B
as the blood brain barrier.
Speaker A
The blood brain barrier.So for the time being, I'm going to, I'm not going to talk about
Speaker B
the blood brain barrier.
Speaker A
This, that's something that's going to be covered in lecture 17.So for the time being, just remember they're important in maintaining and supporting the blood brain barrier.Okay?
Speaker B
Think of these capillaries.
Speaker A
And these, these astrocytes will be important a little bit later when we're talking about lecture 17.
Speaker B
Okay?
Speaker A
So keep that in mind for that.
Describes microglia as CNS phagocytes, ependymal cells lining ventricles and producing cerebrospinal fluid, and oligodendrocytes forming myelin sheaths around central axons.
Speaker A
Now, microglia, they're called microglia because they're really small.They're the smallest out of all the neuroglial cells, and they're their least abundant, okay?And they're basically the phagocytes and macrophages of the central nervous system.
Speaker B
So they come, they are derived from
Speaker A
the same blood cells that your macrophages derive from, which are known as monocytes.
Speaker B
So we are going to talk about.
Speaker A
And that's a white blood cell.So we're gonna.In the next unit, when we talk
Speaker B
about blood and blood cells, we'll get
Speaker A
into greater detail about the five white blood cells that you find in blood.And one of them is monocytes.And their job is they, they become, differentiate into macrophages once they're outside of the bloodstream.Okay?So in the nervous system, in the cns, specifically, specifically, microglia are basically the macrophages of the cns.Their job is to engulf invading microorganisms as well as dead neurons.So neurons that have died, they, the
Speaker B
part, their parts get, that cell debris
Speaker A
gets phagocytosed by your microglia.Then we have a, a third type of neuroglial cell in the central nervous system.These are known as ependymal cells, which translates into.Ependymal translates into wrapping garment.Okay.
And these actually stem from a simple epithelium.From epithelium.And they are found lining the central cavity of the brain.
Speaker B
Okay.
Speaker A
And your spinal cord.
Speaker B
So your brain and your spinal cord.So this right here in the cream color, in the screen color, that's the
Speaker A
brain tissue and, and spinal cord tissue.
Speaker B
But if you were to do a
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cut through your brain or your spinal cord, like a cross section through your spinal cord or a coronal section or a horizontal section right here, a cross
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section through the brain, you would find
Speaker A
that there's hollow spaces inside and that
Speaker B
how those hollow spaces collectively are known
Speaker A
as your brain ventricles.If it's in the inside of the brain or the central canal running through the spinal cord, okay.
And these brain ventricles are, are, have different parts to them.We'll talk about that in lecture 17.These different parts, but lining, and so they're hollow on the inside, okay.And they're filled with a fluid, okay.And that fluid is known as cerebrospinal fluid or csf.
Speaker B
You might have heard of that.Okay.
Speaker A
So when someone gets a split spinal
Speaker B
tap, basically they are, they're cs.A little bit of their CSF is
Speaker A
being removed from their spinal cord.So this, their CSF can be measured for what's in it, different ions, hormones, so on, so forth.
Speaker B
So these ependymal cells, their job is
Speaker A
to make and also helps circulate the cerebrospinal fluid that is found in these ventricles okay?
Speaker B
So right here, what you're seeing is brain tissue.
So this is all brain tissue right here, okay?
Speaker A
So that would be this right here.
Speaker B
And then this space right here, that fluid cavity.Fluid filled cavity.That would be these regions right here.
Speaker A
Okay?These ventricles, these brain ventricles.
Speaker B
Ventricles here.
Speaker A
Or if this was from, taken from the spinal cord.Right, this was taken from the spinal cord.
Then this space right here, that fluid
Speaker B
filled cavity would be called the central canal.Okay?
Speaker A
And lining, just like pretty much all
Speaker B
other hollow cavities in your, in your body, whether it's hollow organs or eventual body cavities, lining the this fluid filled cavity, these ventrals, these brain ventricles in the central canal are these special neuroglial cells that are known as ependymal cells.And if you look at them, they are epithelial.
Speaker A
Okay?
Speaker B
So there are, there are epithelial cells, and in certain parts.So these ependymal cells line the entire, this entire hollow cavity.And in certain parts, the, these epithelial cells, these ependymal cells have this cilia
Speaker A
on them that help take that fluid
Speaker B
that's actually made by these ependymal cells, and they help circulate that fluid throughout these hollow cavities.Okay, now we will talk about what the function of CSF is in lecture 17.
All right, and then the final neuroglial cell type in this cns, they're called oligodendrocytes.Oligo means few, dendro means branch branches, and sites means cells.
Speaker A
Okay?
Speaker B
So please don't call them oligodendrides.That's a common mistake, Right?
Like these guys right here coming off of an axon, those are called dendrites because that looks like a tree branch, right?So these are dendrites, this neuroglial cell right here.Here, it's called oligodendrocyte.Oligodendro means few.It literally translates to few branch cells because they just have a few branches, if you count 1, 2, 3, 4, 5.
Whereas if you compare it to your astrocytes, they have many, many more branches, okay?So that's why they were called oligodendrocytes.Now if you look, these branches actually take themselves and wrap themselves around parts of axons of neurons, right?So here's an axon of a neuron, here's another axon of a neuron, and it's covered in different regions with these parts of oligodendrocytes.So these oligodendrocytes, these processes extend and wrap themselves tightly around portions of neuronal axons and these.And they form these sheaths.They ensheath these parts and they call form these myelin myelin sheaths around axons in the cns.So we're going to talk a little bit more about this in a few slides.What exactly is myelin?Okay, but you should know that some of your neurons in your brain and your spinal cord cord, some of those neuronal axons, are myelinated.So that means oligodendrocytes wrap themselves around those axons, forming these myelin sheets.
But there are also neurons in your CNS brain and spinal cord that are unmyelinated.Okay, we'll talk more about this.Now, you might ask, like, what is this purple guy here?Where's this coming from?Like, how.How does this have a myelin sheath when there's no oligodendrocyte attached to this?This is just how they drew it.Okay, so imagine if I were to draw the.The actual cell body and the process extending to it.
This is not just randomly here.This belongs to another oligodendron.They just didn't end up drawing it in this diagram.
Covers satellite cells surrounding peripheral ganglia and Schwann cells in the PNS, then explains how Schwann cells and oligodendrocytes wrap axons in concentric membrane layers to form the myelin sheath.
Speaker B
Okay, so those were the neuroglial cells in your central nervous system.And then there's two neuroglial cells in your peripheral nervous system.Okay, there's the satellite cells.Those are found surrounding cell bodies that are found within ganglia.
Speaker A
Okay?So remember, cell bodies that lie outside
Speaker B
of the CNS along sp spinal or cranial nerves.Right?They're clustered in these structures, these expanded portions of nerves called ganglia.And those neurons, since they're not encased in your skull or your vertebral column, they need some extra protection.
Speaker A
So they have these satellite cells wrapping
Speaker B
kind of around the cell body.
Okay, now the other type of peripheral nervous system neuroglial cell is known as Schwann cell.So these are the Schwann cells.So Schwann cells do the same thing as oligodendrocytes, but they do it in the pns and they do it a little bit differently, okay, in terms of how they look.But each one of each individual, one of these structures, like this blue guy, this blue guy, this blue guy.This blue guy is one individual Schwann cell.Okay?So it works a little bit differently than with your oligodendrocytes because you can see that this oligodendrocyte, its processes can wrap around multiple axons.Right?So, like this oligodendrocytes, not only does it wrap around this part of the axon, and then this part of the axon leaving a little space in between.But this process of the oligodendrocyte, same oligodendrocyte, wraps itself around this, this other whole other neuron, this other neuronal axon right here and right here.
Whereas with Schwann cells, each individual Schwann cell wraps itself tightly around one portion of one neuron, okay?But ultimately they're doing the same thing.Both Schwann cells and oligodendrocytes form these myelin sheets around certain axons, okay?Most of your peripheral axons.So most axons belong to most motor neurons, and pretty much most sensory neurons are myelinated.
Okay.In your brain, some of your axons, some of your neurons are myelinated, and some are.Some of them are not myelinated.
Speaker A
Okay?
Speaker B
And the job of this myelin is really to form protecting the axons.
That's one job, actually.But one of the more.One of the other jobs, really, really important jobs is to form this insulating sheath that increases the speed of action potentials.Okay, so I'll talk about that in, in a few minutes, but let me talk a little bit more about how.How these Schwann cells and also oligodendrocytes work, how they kind of wrap themselves around and what really is a myelin sheath and what is myelin anyway?Okay, so both Schwann cells and oligodendrocytes, although oligodendrocytes do it slightly differently, wrap concentric layers of plasma membrane around the axon.So if you look over here, this right here.So this right here, this is an axon.And then this guy that kind of
Speaker A
looks like a C shaped structure around
Speaker B
the axon is the schwanzel.Okay?
Speaker A
So this is kind of like a
Speaker B
developing neuron, for example, or a neuron maybe in the periphery that's healing itself.Okay?
So.So this is that part of the neuron that's known as the axon.And here's the Schwann cell, right?So here's the cytoplasm.This is the nucleus of the Schwann cell.And this right here.Well, what's the outer portion of this Schwann cell?Well, that's your plasma membrane.Okay?So your.
Both your Schwann cell, plasma membrane, and also your oligodendrocytes, plasma membranes, you know, because all of this, you know, these processes here, here have plasma membranes, right, are made up of something known as myelin, which is basically a mixture of proteins and phospholipids that form this whitish insulating sheath ultimately around axons.So it's kind of this fatty material, okay, that looks whitish.And its job is to protect the axon and insulate it.Okay.Now during.
So when.When you see first are forming this, you have this schwanzel that kind of envelops this part of the axon.And then it grows, the schwantzel kind of grows and starts wrapping itself more and more in these concentric layers around this portion of the axon.And then once it decides like, okay, I'm done growing, I'm done making these layers, that cytoplasm that's here, the cytoplasm that here, here gets squeezed to the very periphery of the Schwann cell.So the cytoplasm gets squeezed to the most outer layer of the Schwann cell, which is known as the ne neurolemma of the Schwan cell.
And so basically what you end up with is just layers and layers and layers of plasma membrane, Schwann cell, plasma membrane.And remember that a big proportion of this Schuan Schwann cell plasma membrane, as well as the oligodendrocyte plasma membrane, is made up of myelin.So that's why we.Why we call this portion right here the myelin sheath.Okay?
So again, the job of Schwann cells, as well as oligodendrocytes is to make these myelin sheaths, right, that surround axons.
Explains how nodes of Ranvier enable saltatory conduction in myelinated axons and contrasts the propagation speed differences between myelinated and unmyelinated fibers.
Speaker B
Okay?Now when.If you look, look at this neuron, right?
Speaker A
This, this is.
Speaker B
Would be a peripheral neuron.So this would be.And because of its structure, this, it's multipolar structure, I know that this is a motor neuron rather than a sensory neuron, okay?But you can see that this Schwann cell, this Schwann cell is wrapping itself around the axon here.This Schwanzel is wrapping around the axon here.This Schwann cell is wrapping itself around the axon here.Right?So like here it would be one Schwann cell, another Schwan Schwann cell, another Schwann cell, right?Forming these insulating myelin sheets.However, when they wrap, they leave a little bit of axonal membrane free and open right here.
Okay?And what.This is important because in.When neurons axons have myelin sheath surrounding them, they're basically covering big portions of the plasma membrane of the axon.So the plasma membrane of the axon here, here, and here is covered, okay?
And because that's the case, it ends up making the action potential much faster than it would be if it was.If this was an unmyelinated neuron.So I'll explain.Explain that in the next couple of slides, okay?But for the time being, what this, what this is saying is that these, first of all, these gaps right here, there's a name for them.You should know that these gaps here, here, here, or also these gaps in that you see here in central nervous system neurons, okay, Formed by the oligodendrocytes.So these gaps right here, all of these different gaps, those are known as nodes of Ranbier, okay?And Schwann cells on oligodendrocytes in the cns, along with these nodes of Randy Ranby, are these gaps that are found in between myelin sheets in greatly increase your action potential conduction.So they increase basically the speed of action potential.
Initials, okay?
Just like you have insulating sheets wrapping be wrapped around copper wires, okay?Elect or not just electrical wires, which a lot of the time are made up of copper.The job, the.The reason you do that is we'll want to protect yourself from electrocuting yourself.But it also actually increases the speed of electricity because there's not loss of charge.There's nothing loss of, like electrons leaving the wire, okay?They can't escape.So that.That increases the speed of electricity, okay?And so having an insulating sheath around axons of neurons can all that also increase the speed of action potentials, okay?
And that kind of conduction, that kind of action potential conduction where basically, basically the action potential jumps from one node of Ranbier to the next.It looks like it's jumping, okay?That's known as saltatory conduction.Saltatory conduction because saltaire is to jump in Latin.Okay?
So let me explain this a little bit more.
Speaker A
Okay?
Speaker B
So in a neuron that is unmyelinated, okay?In a neuron that does not have myelin sheaths around it.So whether that's in the central nervous system, so there's no oligodendrocytes wrapping themselves around the axon, or whether it's in the peripheral nervous system.So there's no Schwann cells around.Conduction is relatively slow.
Speaker A
I say relatively slow because it's still pretty fast.
Speaker B
But.But compared to a myelinated neuron, it's.It's slower.Okay, why is that?Well, in an unmyelinated axon, action potentials must be regenerated along the entire length of the axon.If you remember that little animation I showed you of a neuron, you know, being.It's all negative here, and then it becomes positive here, and then it goes back to negative income, becomes positive here and goes Back to negative and goes pop becomes positive here.So the action potential even.
Speaker A
So we say, we say the action
Speaker B
potential is conducted or propagated.You're actually kind of regenerating it at every adjacent part of the exonal membrane.Okay?
So in a non myelinated neuron here, you have to depolarize this portion of the neuron here.So here it becomes plus 30 millivolts.And those sodium ions, when they diffuse to this region and you reach a threshold here, at minus 55, those voltage gated sodium channels open and you have a rush of sodium ions in here and you make this become plus 30 millivolts.And those sodium ions will diffuse to here, making it go from minus 70 to minus 55.When it becomes minus 55, voltage gated sodium channels here open and sodium rushes in and it becomes plus 30 millivolts again.Right?So you're kind of going step by step, step.Okay?Now in a myelinated neuron, in the regions where it is myelinated, so here and here with here, right?These regions are these regions right here.
Ions cannot flow across, okay.So they can't.First of all, ions cannot leak out.Okay?There are no current leaks, there's no
Speaker A
loss of electricity density, basically, if you
Speaker B
would think about it like that.And also you don't have to worry about depolarizing this and this entire region.Okay?So for example, when voltage gated sodium channels open in these areas, these node
Speaker A
of ranbiers, which they're really, really, really
Speaker B
highly concentrated in those areas, especially in myelinated neurons, they're even more concentrated there.The sodium ions flow in, making an action potential happen here.Now these sodium ions will diffuse and they'll diffuse.If they were to just diffuse here and this was not myelinated, they would, this, you would have to repeat this process over here first.
But because this is insulated, because this is myelinated, the sodium ions will continue all the way to here and cause voltage gated sodium sodium channels to open here.Sodium ions rush into here, causing another action potential here becomes plus 30 millivolts here.And those sodium ions that came into here, they diffuse here and generate another action potential here.So instead of going action potential, action potential, action potential, action potential, you can go action potential, action potential, action potential, action potential.So basically you're skipping over these parts.You don't have to worry about depolarizing
Speaker A
this part, this part and this part.
Speaker B
Okay, so instead of, you can imagine yourself like if you're walking somewhere from one, one area of the room to the other.And you're going like step by step, like one foot next to putting one foot in front of the other foot in front of the other foot, like touching, you know, the front of your foot to the back of your other foot.That's going to take much longer, longer than if you take like actual normal steps, right?
Like a wide step, that would be much faster.So you can think of it that way.The wide steps, that's saltatory conduction.In a myelinated neuron, you're skipping over parts of the floor, basically, whereas in a non myelinated neuron, you're going step
Speaker A
by step by step, like very like
Speaker B
foot to foot to foot.
And so this is also true.So even though the kind of describing this in, like in this, the saltatory conduction and notes of Ranbier in this slide, talking about Schwann cells here, and also kind of in this image, this also happens in your cns.So neurons that are myelinated in your brain or your spinal cord, they are going to conduct action potentials much faster than the neurons that are not myelinated.
Speaker A
Okay?
Reviews cranial and spinal nerves, defines nerves as collections of axons, and outlines connective tissue sheaths (endoneurium, perineurium, epineurium) along with related terminology.
Speaker B
And to end this lecture, we want,
Speaker A
I want to review what nerves are,
Speaker B
okay, so here, these, first of all, what are these nerves extending from your brain?Right?These are your cranial nerves, okay?And you have 12 of them, okay?You have 12 cranial nerves.And you will learn all of them by name and also number, okay?And then these nerves right here, here extending from your spinal cord, these are called spinal nerves, okay?And you have 31 pairs of spinal nerves.And you will be learning some specific spinal nerves that are that kind of branch from these 31 pairs, okay?You won't be learning all these 31 pairs here, but branches of them.Okay?So what are nerves?
So we've already talked about this, but just to review, nerves are these cable like organs of the PNs that consist of numerous axons, potentially thousands of axons.And a lot of the time, axons, especially when they're long, are called nerve fibers.Okay?Nerve fibers, when they're found with, within the pns or nerve cell fibers, if they're actually neurons in the, in the cns.Because another name for neuron is nerve cell.
Okay?So nerves.So this right here is one nerve, a portion of a nerve, okay?So this would be one of these or one of these.So if you open it up, you can find that you have these guys, you have lots and lots of these axons, potentially thousands of axons in a, in a nerve, okay?
And these axons, the organization of a nerve is kind of similar, and you're going to be using a similar termin terminology to how muscles, your skeletal muscles are organized.So your act, this is an axon.And most of the time, most axons inside of your peripheral, your nerves are myelinated.Not all.Okay, all motor.All.I'm sorry, all somatic motor axons are myelinated.Not all visceral motor axons are myelinated, but that.This right here is a myelin sheath.Just outside of that myelin sheath, okay, which lies just outside of the axonal plasma membrane.
But just outside of the myelin sheath, you have a loose connective tissue covering here.Here, that's known as the endoneurium.So not endomysium, that will be found around a skeletal muscle cell, but around a exonal neuronal axon.Just outside of myelin sheath, usually is your endoneurium.And if you look, several axons, right, Are bundled into one bundle.And what is the name of this?Just like in muscle fibers, this is known as fascicle.Okay, so this is a fascicle.And what is the connective?It's a fibrous connective tissue sheath covering around this that would be called perineurium.
So similar to perimysium, but it's called perineurium.Okay?And then you have several fascicles bundled into one big nerve.And the dense, irregular connective tissue sheath covering around, making up the outer layer of a nerve, covering the nerve is known as not epimysium, but epimerium, epineurium.Okay?
And then finally, just some other terminology.Another name for neuron is nerve cell.Okay?So another name for neuron is nerve cell.Okay?
Another name for accent, especially when it's a long axon, okay?Found within
Speaker A
a nerve.
Speaker B
Although some people even call long accents.Within the cns, they call that the nerve fibers.Okay?So fibers are long axons.I will refer to nerve fibers as the long accents found within nerves.Okay, and then what's a nerve?It's a collection of nerve fibers in the pns.So again, nerve, whenever you hear the nerve, at least in our class, right, when you hear the nerve, the word nerve, think that's part of the pns.That's.Those are these structures here and here.And ultimately they're just collections of peripheral axons.Okay, so those are.What's in here would be your sensory and your motor.Accents of sensory and motor neurons.Okay.
Speaker A
Okay, so this is lecture 16.