Muscle 2- Skeletal muscle organs

Muscle 2- Skeletal muscle organs


– Now skeletal
muscle tissue is one component of a skeletal muscle organ. We know that the definition
of an organ is a structure that is composed of many
different kinds of tissues that all work together
for a common function. A skeletal muscle
organ is composed of multiple different
kinds of tissues, one of which, the primary one of
which is skeletal muscle tissue. When you look
at a skeletal muscle organ, we’re going to dive in
and look at basically the organ level all the way
down to the cellular level and smaller than cellular level,
in order to kind of understand how the skeletal
muscles function. But there’s a couple of things
that you can know just from looking at the big
picture organ itself. First of all, most skeletal
muscles attach to bones. We’ve already done the bone lab
and we’ve done the joint lab. So if you can imagine that skeletal muscle organs
attach to bones and span joints, we can shorten
the skeletal muscle organ and cause a movement
to take place. In order
for this to happen we need two, at least two attachment points.
And the attachment points– this is a picture,
I can’t draw on it. But the attachment points, we have an origin attachment and
we have an insertion attachment. The origin, and it
gets super gray and muddy, and do we really want
to spend a lot of time debating
and figuring this out? No, not in my class. The origin is the attachment
that moves the least and the insertion is
the attachment that moves the most.
Honestly, it doesn’t matter to me if you distinguish
between those. The important thing is knowing
where our attachments are. Then once you’ve identified
the attachments for a skeletal muscle you can actually look
at the fiber direction. Now, each one of these fibers is
anatomically a fascicle. And I’m telling you that
now and we’re going to look at it and write it
down in the next section. Because the skeletal muscle
organ is made up of bundles of fascicles and the fascicles
are what you can actually see, the long thin–
what are they? Like you eat them,
like, you can shred. You can shred a piece of steak,
right? There’s like an easy way to cut
the steak with the grain and then there’s like
a hard way to cut the steak, where you are cutting across
all the little shredded– does anybody know what
I’m talking about? I hope you’re vibing
me right now because otherwise,
I’m sorry. But these are gross anatomy structures that you
can actually see. Now, what’s the whole point?
The point is if you identify the fiber direction and you
identify the attachments, you can actually figure out the
action of the skeletal muscle. And that happens because
skeletal muscle shortens along the fiber direction.
What? That means the fiber
direction is this way from, let’s say, sternum.
Sternum, this is pec major, sternum to, whoa,
humerus. And if these fibers shorten, look at what’s going to happen
to the movable attachment, which is the humerus. The humerus is actually
going to move toward the torso, and that happens because of the shortening of these
muscle fibers. If you know these things you
can figure out the action. The action is the movement
that the muscle causes. Now let’s see what else
do you need to know. Usually muscles come in pairs. They come in movement pairs. One muscle causes one movement. One muscle causes A-D-duction and the other muscle in the
pair causes A-B-duction, and those muscle pairs are
called antagonistic pairs. Physiologically a muscle
can’t actually relax itself. It needs its antagonistic pair to stretch back out
into a relaxed state. Which is kind of an
interesting thing that we’ll spend a little
bit of time thinking about, but we won’t get a whole
lot of details in anatomy. I think the entire skeletal
muscle organ is surrounded in a connective tissue
sac called the epimysium, and that’s where
we’re going to start. We’re going to look at and
then the entire muscle organ is made up of various
other things. So now we’re going to go into
what is this hierarchical organization
of skeletal muscle.

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