- [Voiceover] Muscle tissue comes in three different types.
The first type to talk about is skeletal muscle.
Now skeletal muscle is growing muscles
that are attached to your bone
and muscles that move your body parts.
So if you think, let's raise your hand
or move your leg, those are skeletal muscles
performing that voluntary action.
So if you are constantly thinking about something,
you want to do something, a movement,
that movement that you can do is a voluntary movement.
Now these skeletal muscles are multinucleate.
That means they have multiple nuclei per cell.
That's kind of unique.
Most cells have one nucleus.
Well these skeletal muscles are so large and so long,
that they actually are multinucleate.
Cardiac muscle, now cardiac, you think heart.
Cardiac muscle is the muscle of the heart
that allows for the contraction of the heart.
Now if you find cardiac muscle anywhere else,
now you really shouldn't,
because cardiac muscle is only in the heart.
Now cardiac muscle is involuntary.
You cannot think heart speed up, heart slow down.
No, you can't do it.
Sure, you can speed your heart up by working out.
You can slow your heart down a little bit by relaxing.
But can you just at instant notice think, speed up?
Doesn't work that way.
So it's involuntary muscle.
And they typically have a single nucleus.
Then we have smooth muscle.
Now smooth muscle surrounds hollow structures.
That's pretty vague and pretty general,
because it's around a lot of things.
You can think of any hollow structures like your stomach,
your small intestines, large intestines,
a lot of your blood vessels,
they're all going to contain smooth muscle in the wall
that'll help to contract and move the substance through.
Now you're thinking, well, digestive tract,
that's stomach and intestines, cardiovascular,
that's blood vessels, they're all involuntary.
You cannot control them.
That means smooth and cardiac are both
involuntary control mechanisms.
And again, smooth muscle has a single nucleus.
So really, cardiac and smooth share features
of the involuntary.
Skeletal, that's voluntary, you can control those.
So a little bit different that way.
Here's a small micrograph picture
of the skeletal muscle tissue.
The one on the left, the kind of purplish shape,
is the actual view through the microscope.
The one on the right is the artist's rendition
of what the view looks like.
You can see how the muscle cells are going left to right.
They actually extend beyond this field of view.
So very long muscles, they have very many nuclei,
they're multinucleate.
If you notice those little vertical lines,
the ones that are going along each individual muscle cell,
kind of giving you a strip pattern,
those are called striations.
Now, those little tiny lines are striations,
they're made from the protein that makes the actual cell.
Here's cardiac muscle.
It looks kind of similar.
You still have those striations.
But now we have these very dark bands every so often.
Those dark bands every so often are intercalated discs.
The intercalated disc is how two cells are joined together,
through your intercalated disc.
Now also, if you notice, there's a little more space
in between the cells, that's that little off-white area.
So cells aren't quite packed as tightly.
And here is smooth muscle.
If you notice, smooth muscle does not have any striations.
All you're seeing is many little cells all packed together.
The cells are almost spindle-shaped.
So tight little spindles, or diamond shapes,
they're kind of put together.
They make sheets of muscle.
These sheets are what wrap around the hollow organ.
So our skeletal, cardiac, and smooth muscle,
some views showing what they look like.
The next category, the nervous tissue.
The nervous tissue really only has one primary cell,
but then a whole lot of secondary cell types.
The primary cell is going to be the neuron.
The neuron is this specialized cell
that actually generates electrical impulses
and then transmits that electical impulse
to the next neuron or next tissue.
These electrical impulses,
these are our controlling mechanisms.
When you think you want to raise your arm,
or you want to move your leg,
your brain, or spinal chord,
are going to send these electrical impulses
down to the muscle.
It's these electrical impulses
that will stimulate the muscle to move.
Well, the electrical impulses are also
what allow you to think.
All those thoughts,
all the processes going on in your brain,
are all electrical impulses.
So, in general, a neuron has three main parts.
It has the structural components
the body, dendrite, and axon.
The cell body is where the nucleus is,
it's more kind of a main chunk of the actual neuron is.
The dendrites and axons are going to be protrusions
or like branches coming off the cell body.
The axon itself will carry information
away from the cell body.
The dendrite will bring information toward the cell body.
Because what happens to neurons is
one neuron might connect or synapse with another neuron.
And you just sent information from point A to point B.
So that first neuron can send information down
from the cell body to the axon.
Then that axon will give the information
to the dendrite of the next neuron.
So axons send information away from the cell body,
dendrites receive information
and bring it towards the cell body.
Now the secondary cells, they're not
transmitting impulses, they're not transmitting
electrical impulses at all, they're strictly support.
The glial cells are meant to support.
They come in many different sizes,
many different shapes, many different functions.
Don't worry about all the different parts and pieces.
What we're focusing on is the fact
that glial cells are there to support the neuron,
to keep the neuron healthy, keep the neuron viable.
Because once a neuron is killed off
you may never get another one to replace it.
Neurons are pretty much there for life.
So here's your micrograph on the left-hand side,
so you can see right through your microscope,
the very large purple cell right in the mmiddle
with all the protheses or branches coming off,
that is the neuron.
The central core right there, you can see the cell body,
then you have an axon going up,
and a whole bunch of dendrites
going off to the side and down.
All the little purplish blackish dots around the neuron,
those are all the glial cells,
those are actually the nuclei of the glial cells,
but we can call them glial cells.
Those are all there to support, to help,
to protect that neuron, to make sure it stays healthy,
functional, and to make sure everything is functioning 100%.
If your neurons go down, your nervous system goes down.
So neurons are kind of important.