okay welcome back anatomy today we're going to talk about cells of the nervous
system in my class we have a quiz tomorrow and it's covering both the
neurons and neuroglia. So these were two separate cell or two separate lectures
in class but we're combining them into one for the purpose of studying for our
quiz so just reviewing we have neurons and we have neuroglia the neurons are
the ones that you typically think of as a nerve cell so this is a typical neuron
and we need to be able to label a neuron like this we need to be able to classify
it according to its structure and its function. So first of all let's talk
about the fact that a neuron cannot reproduce so any any damage to a neuron
is going to have a long-lasting effect because we can't make any more of
them and that's different from the other cell, the neuroglia, can reproduce I'm
the neurons can transmit impulses in neural glia can not so there's two big
differences between the two types of cells so the nerve the neuron has three
main parts so the dendrite the pieces out here that look like tree branches
Dendra comes from the word tree and here is the soma which is the cell body not
the green in the middle that's the nucleus and then we have this long
extension here called the axon so the cell body is what you would think of as
a typical cell, it contains cytoplasm mitochondria nucleus the other
organelles that that all cells would have it needs to make proteins it needs
to make energy all of those things out here the dendrites for sensory cells
those that say are in your skin we're going to call these dendrites receptors
so that's where we're actually going to receive information the job of the
dendrites is to take information to the cell body now the axon its job is to
take body or information away from this out body so maybe it is going to another
cell to send impulses to neurons or maybe it's going into an effector cell
like your muscle or a gland or an organ and telling another part of your body
what to do so it might be transmitting signal
to another signal transmitting cell or its Indian sending signals to a style
telling it what to do alright so here's some other features that you could
identify in a typical neuron: one is it has the axon terminal here at the end
that's where we're going to release our chemical messengers our chemical
messengers are called neurotransmitters we have lots of different
neurotransmitters each for different purposes so information is going to be
sent out of these axon terminals and received from another receptor on
another cell so we talked about acetylcholine and muscle cells in the
last chapter that would be good example here this coding that you see on the
outside of the cell that's called a myelin sheath so myelin we find on many
axons and that insulates the the axon and it protects it from damage because
remember we can't replace it if it's gone it's gone and so that's going to
help speed up signal transmission as well the other thing in between each of
these cells making up the myelin sheath there is an exposed accent and that
exposed axon will be called the node of ranvier so the node of ranvier is the
space in between on the schwann cells in this case that that allows for impulses
to travel so the importance things about the myelin sheath here is that it
creates a faster transmission so this transmission is called Saltatory
conduction saltare means "to hop" so what I see here is a depolarization only
happening at the axon if you remember an order for depolarization to occur ions
have to cross the membrane so sodium is going to rush in potassium is going to
rush out if I have another cell wrapped around that acts on it can't happen
there so we can only have depolarization where the axon is exposed so it's going
to jump over that insulation and that allows it to go very quickly so over
here this cell has statutory conduction on
and the one on the bottom has constant conduction so every single nanometer
along that accent has to depolarize so that's going to make that a much slower
transmission okay so we know the basic pieces and parts of a neuron now we want
to be able to classify neurons so we classify them either according to
function which refers to the direction the impulses traveling with respect to
the central nervous system or we classify them according to their
structure which is referring to how many extensions are connected to the body so
here I see this arrow is showing me the direction the impulses traveling so this
is going towards the cns and this one is through the cns and this is coming out
the cns so going toward the cns will call the sensory going through is enter
and going out is motor and I have a separate slide on each of those and over
here you see this isn't cell body it has two extensions so I'm going to call that
one bipolar this one only has one extension connected to it so i'll call
it unipolar this one has several look at all those dendrites around the body and
we'll call that one multiple polar so down here this is the typical neuron
that you see it's the most common so whenever you have to diagram and iran
you're looking at a motor neuron that's multi-polar so this is the structure of
both interneurons and motor neurons and bipolar up here you see there's two
extensions connected to the cell body so one going in and one going out so one
dendrite one axon bipolar are found in your special senses like your eyes in
your nose and your mouth in your tongue and so the dendrite remember is called a
receptor the unipolar down here so see there's only one extension connected to
that and then it branches into proximal and distal extensions so we find those
in our general census so what's the difference between a general sense and a
special sense sorry general senses are found all over your body so your sense
of touch is a general sense proprio reception which
to do with tension in your muscles the tendons in your muscles since when
there's a difference in tension and you have a tendency to like counteract it
umm so so senses that are found all throughout your body are called general
senses so those in our skin that maybe we feel the pinprick in the common
example that would be a unipolar neuron whereas those that are found in specific
areas so i only have rods and cones in my eyes i don't have them anywhere else
those are called special senses and those are going to be bipolar so
functionally we classify them according to the direction the impulses traveling
with respect to the CNS so now that we just talked about a unipolar neuron we
can look at a unipolar in action so here is some skin here is some receptors
those receptors are picking up some signal maybe you touched something that
was hat or cold or maybe it was sharp or smooth or rough so you have these sense
receptors here those are the dendrites of a sensory neuron so that sensory
neuron then is an afferent neuron meaning the impulse is going toward the
CNS so with the sensory neuron the dendrites and the cell body are both
outside in the peripheral nervous system but over here I'm looking at the spinal
cord so here you have a gangly on and that's where you find a cluster of cell
bodies and those then are outside of the CNS but the axons extend into the cns
connected to those are associative nerves here's an associative nerve its
branches aren't very long but it does have many extension so we know that's a
multipolar neuron so that's entirely within the cns so this would be entirely
within my spinal cord or my brain and what it's doing is simply connecting a
motor nerve to this would be my motor nerve to a sensory nerve so the sensory
nerve picks up information from your external or your internal stimuli takes
it to the CNS hangs out in the spinal cord comes back out or it goes up to the
bridge and decides what to do and then it comes
back down and then it sends it signal off through the motor nerve the motor
neuron a multipolar neuron so here I see the motor neuron is connected to
hopefully you recognize that as muscle so you see the fascicles all in bundles
that make up the muscle so this is apparent it's sending signals away from
the spinal cord the brain and spinal cord over here again sensory cell taken
information in and then it's handed off to the efferent neuron or the motor
neuron which takes it out to a gland an organ for a muscle hmm so this is just
repeating that this is how cells are communicating so you see the sensory
associative motor I like to spell the name Sam because it helps me remember
that or you can think a ferent in enter in between and motor going out or
efferent going out so those are the neurons the the ones that can actually
send signals but can't reproduce now we're going to talk about the neuroglia
the ones that can't send signals but they can reproduce so neuroglia means
nerve glue glue and sometimes you just see it called glial cells and that's
fine so together they support they insulate they protect neurons because
remember once the neurons are gone they're gone so we need to protect them
as best we can so there are six of them for are found in the cns two are in the
pns so pay attention to which is which so this is an astro sight I don't know
if you can tell how big that is but think all these other little cells you
can hardly see right so an astrocyte is very large it's the most numerous of
your neuroglia so those sound like good test questions um it's also star-shaped
which is where it gets its name Astro refers to the star so what it does it
anchors on neurons to their blood supply it anchors them to capillaries and so it
can do a little bit of filtering perhaps on it supports the blood-brain barrier
and and that has to do with some epithelial cells within the
nervous system and it also controls chemical environment by picking up
release neurotransmitters we want to recycle them so we can keep using them
and excess ions we don't want depolarization happening just any old
time we want it kind of coordinated and in specific moment so often on not so
often hopefully if we have some injury to our brain and astrocytes kind of make
up the scar so if you think of a scar on your skin is built up south you have
some built up cells in an injured area so it fills the gap fills the space and
those are the astrocytes mm-hmm microglia hopefully you recognize the
prefix micro means small they're small phagocytic cells so phagocytic means
that they engulf and eat foreign things so your white blood cells are our
phagocytic cells and microglia serve the same function as white blood cells do in
your central nervous system so they're considered the primary immune defense
and then they're going to gobble up bacteria and other things that don't
belong debris dead cells once your brain cells are gone we said they don't
reproduce so we need to get rid of them I've been demo cells so these are
modified perhaps epithelial cells they have cilia and they line the brain in
the spinal cord so here you have an open space so you have some ventricles in
your brain that have open spaces when you look at the spinal cord there's some
open space in there as well so cerebral spinal fluid is in those spaces and
cerebral spinal fluid has antibodies in it so it protects us from infections it
also has nutrients so um that kind of keeps the help of all the cells
basically the cilia they work to brush that cerebral spinal fluid so it keeps
it circulating kind of keeps it fresh so that's the purpose of the ependymal
cells so this is the last one that's found in the central nervous system all
the ones I've talked about so far are CNS so astrocytes microglia epic
demo sales and oligodendrocytes are all found in the cns and sometimes any of
these words they might drop the site and put glial on the end so it's an illegal
gender site as in singular or collectively
oligo gender glia that's hard to say mmm so what I see these blue cells these are
the oligodendrocyte the yellow one is your neuron so what it's doing it has
these long extensions that wrap around and around and around and around around
around the axons to protect them so that we can keep sending signals and not have
any mechanical damage perhaps to those axons again we talked about South
dettori conduction so it allows for the quick impulse it insulates the cell as
well two cells left so oligodendrocyte is in the cns schwann cell similar cell
in the pns so down here you see the oligodendrocyte notice its whole body is
outside of the cell here you have the schwann cell Theodore shots run we
learned about in ninth grade with the South theory so this cell wraps itself
around and around and around around the axon just like these extensions did so
the oligodendrocyte does in the cns what the schwann cell does in the pns it
creates see here we see it going around and round and round and round so it
creates the protective coating of the axon and helps to speed up neural
transmission finally we have the satellite cell satellites go around and
around bodies right so this satellite is going around and around the cell bodies
of those neurons that are in the pns so they're more likely to get hurt out and
about right outside of our brain and spinal cord we have a lot more I bump
into things all the time so we want to protect these as much as possible so
they're going to put a protective coating on the outside of the cell body
so that it can be as safe as possible let's say sometimes these do become
injured and then they start to send lots of signals related to pain so um they're
associated with chronic pain nobody wants that so that's it we got the
neurons we classified them functionally and structurally we
the neuron pieces and parts so we need to be able to diagram a neuron and then
we talked about neuroglia so first we should know to differences reproduction
and transmission between neurons in regalia we should know for neuroglia
that are found in the cns and two they both start with an s so that makes it
easy to that are found in the pianist so for all six of those you need to know
their characteristics by description you need to know the function of each so I
think you can do it so I hope that's helpful good luck on your quiz