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- [Voiceover] In this chapter

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we're going through the muscular system.

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We're looking at some--

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Let's start here.

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This is what you'd look like pretty much

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if you pulled all your skin off.

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Kind of a weird look to it.

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Pull the skin off,

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pull all the fascia that
held things together,

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and here's where we are.

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What we do in this slide is go through

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and identify some of the major muscles.

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Start with the pectoralis major.

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Now the pectoralis major, you see it

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obviously both sides of the body,

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it's drawing the arm forward.

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What happens is, it's literally

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sticking your arm out in front of you.

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It's pulling that arm forward
in front of your body.

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Serratus anterior.

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Think of the term serratus
as like a serrated knife.

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The edges are kind of jagged.

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This is going to help
you to raise your arm up,

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pulling that shoulder blade,
that scapula right in the back,

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it's helping to pull that forward,

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so kind of raising, bringing the arm up.

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Serratus anterior.

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The biceps brachii, that large muscle

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that's right on the top of your upper arm,

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on the front or anterior side.

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When it contracts you bend at the elbow.

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Rectus abdominus, well everyone knows

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that is the six-pack muscle.

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Well, that six-pack muscle's
there in every single person.

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It's meant to help compress
the abdominal cavity,

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meant to help bend your
vertebrae, your backbone.

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So everyone has a six-pack.

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Question is, is it visible or not?

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You can always work on that.

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External oblique.

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These are the muscles that are around

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the more lateral, more
outside edges of your abdomen.

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You could help to compress
the abdominal cavity again.

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It helps to have you twist
at the waist a little bit.

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Adductor longus helps
you to flex your thigh.

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Now, what's flexing the thigh?

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It's move your entire leg forward,

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as if you're kicking a soccer ball,

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you're going with the leg forward.

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The adductor longus.

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Sartorius.

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It's that long, thin strap there.

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Well, if you look at
what it says it's doing,

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it's bending the thighs at the hip,

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bends lower leg at knee,
rotates thigh outward.

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What's that doing?

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It's causing your leg to be curved over,

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so you're crossing your
legs in front of you.

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Sitting, your legs interwined,

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and your ankles underneath
your upper legs.

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Quadriceps group, all those
muscles of your thigh.

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Their action?

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Helps to cause your knee to extend.

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It straightens out your leg at your knee.

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Tibialis anterior.

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That's that muscle that's right next to

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your shin bone or your tibia there.

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It's going to help take your toes

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and pull your toes up towards your knee,

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so it flexes the foot towards the knee.

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Deltoid that's on the lower
part of your shoulder.

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That's going to help you raise your arm

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away from your body, so you're
going straight out away.

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Trapezius, more commonly
known as your traps,

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is going to help brace your shoulder,

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or pull your head backwards.

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Triceps brachii, they
do the exact opposite

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of those biceps brachii.

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The triceps brachii are on the
back side of your upper arm,

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causing the elbow to straighten.

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Latissimus dorsi, you might have

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heard of them as your lats.

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The latisimus dorsi is
drawing the arm backwards.

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It's partially pulling the
arm back away from the body.

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Gluteus maximus, the major thing here

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is it causes thigh extension.

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It's going to take your
leg if you're standing up

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and cause your leg to go backwards.

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The hamstrings.

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The hamstrings are
doing the exact opposite

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of the quadriceps.

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The hamstrings cause your knee to bend.

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Gastrocnemius, that's your calf muscle.

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It causes you to point your toes downward,

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so it's pulling your heel up

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and pointing your toes downward.

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The Achilles tendon.

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All it's doing is holding
that gastrocnemius muscle

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into your ankle, specifically
the heel part of your ankle.

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What are these muscles really doing?

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All those muscles are contracting.

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That's what every muscle has in common.

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Every muscle contracts.

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The contraction is shortening
the distance the muscle runs.

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In the case of skeletal muscle,

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contraction of muscle moves the bone.

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Now, when are these muscle
groups are considered

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synergistic or antagonistic?

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In the case of synergistic,
they're working together.

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The several muscles, to
be precise, four muscles

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of your quadriceps,
they're working together.

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They're synergistic.

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The three muscles of your hamstrings,

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again, they're working
together, synergistic.

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Antagonistic is the opposite.

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Antagonistic, they do the opposite.

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They don't want to work together.

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Biceps brachii, triceps brachii,

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they perform opposite actions.

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Biceps brachii bends the elbow.

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Triceps brachii straightens the elbow.

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Every one of these skeletal muscles

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has what's called an origin and insertion.

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The origin is where the muscle attaches

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and does not move.

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The insertion is also
where the muscle attaches,

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but this is the side that does move.

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In this particular example you can see

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the biceps brachii and
triceps brachii muscles.

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Let's look at the biceps brachii.

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You can see it's attached
up by the shoulder

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and then down past the elbow.

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Well, you cause your
biceps brachii to contract.

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You tighten.

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You bend your elbow.

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Which is moving?

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Is your shoulder moving,

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or is the arm just past the elbow moving?

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Well, your arm just past
the elbow is moving.

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It's being pulled towards the shoulder.

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Up in the shoulder of the origin,

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insertion will be down towards the elbow.

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The origin's up by the scapula.

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Insertion is down past the elbow.

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These muscles themselves are built upon

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units and units and units.

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They're all tiny little pieces that are

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wrapped together to larger
and larger and larger.

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There's this term called fasicle.

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A fasicle is a bundle of
muscle fibers wrapped together.

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Kind of think if you took
a whole bunch of straws

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and put them together, then
wrapped Saran Wrap around them.

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The Saran Wrap would be
the connective tissue

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holding the straws in place.

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The straws are the muscle fibers.

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Now, these muscle fibers, they're cells,

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long, thin, tube shaped, and many nuclei,

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so they're referred to as multinucleates.

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You can have one muscle
fiber, or one muscle cell

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that's 10 inches long and
can have dozens of nuclei.

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It can have so many nuclei
because as it's being formed,

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it's just multiple cells
all being fused together.

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Inside that muscle fiber,

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you're going to find actin and myosin.

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These are the two filaments
that are really meant

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to overlap and cause movement.

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This picture, if you
look at the top right,

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you can see there's the whole muscle.

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All those little sections you see there,

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that one that's pulled
out, that's a fascicle.

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Within each fascicle, you can
see each individual piece.

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That's a single muscle cell.

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Now, inside the muscle cells,

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you have those individual myofibril.

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What are they?

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All they are is literally tons
and tons of little filaments.

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On the histology in the bottom,
in the actual photograph,

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you can notice that the
muscle cell is labeled.

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That one band is the same exact thing

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as what you see drawn above it.

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So one long, thin cell.