- [Voiceover] In this chapter
we're going through the muscular system.
We're looking at some--
Let's start here.
This is what you'd look like pretty much
if you pulled all your skin off.
Kind of a weird look to it.
Pull the skin off,
pull all the fascia that held things together,
and here's where we are.
What we do in this slide is go through
and identify some of the major muscles.
Start with the pectoralis major.
Now the pectoralis major, you see it
obviously both sides of the body,
it's drawing the arm forward.
What happens is, it's literally
sticking your arm out in front of you.
It's pulling that arm forward in front of your body.
Serratus anterior.
Think of the term serratus as like a serrated knife.
The edges are kind of jagged.
This is going to help you to raise your arm up,
pulling that shoulder blade, that scapula right in the back,
it's helping to pull that forward,
so kind of raising, bringing the arm up.
Serratus anterior.
The biceps brachii, that large muscle
that's right on the top of your upper arm,
on the front or anterior side.
When it contracts you bend at the elbow.
Rectus abdominus, well everyone knows
that is the six-pack muscle.
Well, that six-pack muscle's there in every single person.
It's meant to help compress the abdominal cavity,
meant to help bend your vertebrae, your backbone.
So everyone has a six-pack.
Question is, is it visible or not?
You can always work on that.
External oblique.
These are the muscles that are around
the more lateral, more outside edges of your abdomen.
You could help to compress the abdominal cavity again.
It helps to have you twist at the waist a little bit.
Adductor longus helps you to flex your thigh.
Now, what's flexing the thigh?
It's move your entire leg forward,
as if you're kicking a soccer ball,
you're going with the leg forward.
The adductor longus.
Sartorius.
It's that long, thin strap there.
Well, if you look at what it says it's doing,
it's bending the thighs at the hip,
bends lower leg at knee, rotates thigh outward.
What's that doing?
It's causing your leg to be curved over,
so you're crossing your legs in front of you.
Sitting, your legs interwined,
and your ankles underneath your upper legs.
Quadriceps group, all those muscles of your thigh.
Their action?
Helps to cause your knee to extend.
It straightens out your leg at your knee.
Tibialis anterior.
That's that muscle that's right next to
your shin bone or your tibia there.
It's going to help take your toes
and pull your toes up towards your knee,
so it flexes the foot towards the knee.
Deltoid that's on the lower part of your shoulder.
That's going to help you raise your arm
away from your body, so you're going straight out away.
Trapezius, more commonly known as your traps,
is going to help brace your shoulder,
or pull your head backwards.
Triceps brachii, they do the exact opposite
of those biceps brachii.
The triceps brachii are on the back side of your upper arm,
causing the elbow to straighten.
Latissimus dorsi, you might have
heard of them as your lats.
The latisimus dorsi is drawing the arm backwards.
It's partially pulling the arm back away from the body.
Gluteus maximus, the major thing here
is it causes thigh extension.
It's going to take your leg if you're standing up
and cause your leg to go backwards.
The hamstrings.
The hamstrings are doing the exact opposite
of the quadriceps.
The hamstrings cause your knee to bend.
Gastrocnemius, that's your calf muscle.
It causes you to point your toes downward,
so it's pulling your heel up
and pointing your toes downward.
The Achilles tendon.
All it's doing is holding that gastrocnemius muscle
into your ankle, specifically the heel part of your ankle.
What are these muscles really doing?
All those muscles are contracting.
That's what every muscle has in common.
Every muscle contracts.
The contraction is shortening the distance the muscle runs.
In the case of skeletal muscle,
contraction of muscle moves the bone.
Now, when are these muscle groups are considered
synergistic or antagonistic?
In the case of synergistic, they're working together.
The several muscles, to be precise, four muscles
of your quadriceps, they're working together.
They're synergistic.
The three muscles of your hamstrings,
again, they're working together, synergistic.
Antagonistic is the opposite.
Antagonistic, they do the opposite.
They don't want to work together.
Biceps brachii, triceps brachii,
they perform opposite actions.
Biceps brachii bends the elbow.
Triceps brachii straightens the elbow.
Every one of these skeletal muscles
has what's called an origin and insertion.
The origin is where the muscle attaches
and does not move.
The insertion is also where the muscle attaches,
but this is the side that does move.
In this particular example you can see
the biceps brachii and triceps brachii muscles.
Let's look at the biceps brachii.
You can see it's attached up by the shoulder
and then down past the elbow.
Well, you cause your biceps brachii to contract.
You tighten.
You bend your elbow.
Which is moving?
Is your shoulder moving,
or is the arm just past the elbow moving?
Well, your arm just past the elbow is moving.
It's being pulled towards the shoulder.
Up in the shoulder of the origin,
insertion will be down towards the elbow.
The origin's up by the scapula.
Insertion is down past the elbow.
These muscles themselves are built upon
units and units and units.
They're all tiny little pieces that are
wrapped together to larger and larger and larger.
There's this term called fasicle.
A fasicle is a bundle of muscle fibers wrapped together.
Kind of think if you took a whole bunch of straws
and put them together, then wrapped Saran Wrap around them.
The Saran Wrap would be the connective tissue
holding the straws in place.
The straws are the muscle fibers.
Now, these muscle fibers, they're cells,
long, thin, tube shaped, and many nuclei,
so they're referred to as multinucleates.
You can have one muscle fiber, or one muscle cell
that's 10 inches long and can have dozens of nuclei.
It can have so many nuclei because as it's being formed,
it's just multiple cells all being fused together.
Inside that muscle fiber,
you're going to find actin and myosin.
These are the two filaments that are really meant
to overlap and cause movement.
This picture, if you look at the top right,
you can see there's the whole muscle.
All those little sections you see there,
that one that's pulled out, that's a fascicle.
Within each fascicle, you can see each individual piece.
That's a single muscle cell.
Now, inside the muscle cells,
you have those individual myofibril.
What are they?
All they are is literally tons and tons of little filaments.
On the histology in the bottom, in the actual photograph,
you can notice that the muscle cell is labeled.
That one band is the same exact thing
as what you see drawn above it.
So one long, thin cell.