before we get into our discussion of the specific muscles that are affecting the joints that we just
discussed let's talk a little bit more about the specifics of what muscle actually is in
order to understand that we need to understand the properties of muscular tissue so I'm going
to discuss four specific properties these are not just unique to skeletal muscle which will be our
focus but of the three main categories skeletal smooth as well as cardiac muscle so when you're
talking muscular tissue one thing that you need to understand is that it's electrically excitable
what in the heck does that mean this means that it can can change due to some type of external
stimuli be it something electrical or in terms of hormones and we'll talk about that when we get
into smooth muscle so you can have a stimuli so an ion change in terms of the muscle tissue allowing
for an action potential to allow for contraction so you have these specific two muscles as well as
nerve cells and you'll get into that quite a bit more with Dr. Sullivan in subsequent videos now
all muscle tissue is capable of contracting so with the action potential that allows for those
sarcomeres within the skeletal muscle to contract allowing for the muscles to move and move the
bone in turn so contractility is a property of muscular tissue extensibility is a big one the
ability to stretch now depending on what type of muscle tissue you're talking about you can
have quite a bit of extensibility or less so so skeletal muscle is kind of in between cardiac and
smooth muscle it's kind of one of the in-between and the connective tissue that's associated with
the muscle tissue will really play a role in terms of only allowing it to stretch so much and lastly
elasticity so you have the extensibility which is the ability to stretch elasticity is the ability
for it to go back to its original shape without damage so elasticity plays a big as big a role
in terms as extensibility all right functions of muscular tissue obviously the big one producing
body movements when you have the contraction of the muscle it's going to pull the bone allowing
for movements to occur at the joints so without muscles you're not going to have body movements in
addition many of the muscles of your body are continuously contracting not really forceful
contractions but smaller contractions allowing for the stabilization of body position allowing
for me to sit upright or if I were to stand up you would have those muscles of the lower limb as
well as the pelvis stabilizing your body positions additionally muscles can store and move substances
within the body calcium is a big one calcium keeps coming back particularly when we're talking about
musculoskeletal system so you have the storage of calcium and some you have blood as well that
are gonna is going to play a big role in terms of being stored within the body for the muscles and
lastly producing heat think about it when your muscles contract this is going to release some
heat one of the best examples a way to really visualize this let's think about when you're
really really cold what's one of the first things you're gonna do your teeth are going to kind of
chatter or you're gonna shiver throughout the body that is allowing for muscles to contract
and allow for heat to be released now we are going to focus mainly in terms of skeletal muscle cells
when we're talking about the musculoskeletal system we're talking skeletal muscle cells
now both skeletal muscles as well as cardiac muscles are referred to as striated muscles and
all this means is that the two main contractile protein filaments which are myosin and actin
these two particular proteins are going to be very
well organized into what's referred to as a sarcomere
so this organization when you're looking histologically at these particular cells will
allow for this very organized appearance that you see in skeletal muscle cells and cardiac
muscle cells now skeletal muscle cells for the most part are voluntarily controlled okay so
you think about it I'm thinking about moving my elbow I'm contracting the muscles that are going
to allow that to happen now it's important to note that not all skeletal muscle cells have a purely
voluntary component there is going to be some involuntary control for some specific muscles
so we'll talk about that in more detail later now the major difference between the skeletal
muscle cell and the cardiac muscle cell well obviously the main one is that cardiac muscle
cells are solely located within the heart so they're making up the the walls of the heart
another another important part is that this is going to be involuntarily controlled and what's
very unique and you'll go into quite a bit more depth with Dr. Fox and subsequent lectures is
that cardiac muscle cells have their own pacemaker within so whereas you're going to have nerves that
are going to allow for skeletal muscle cells to send that signal to allow for an action
potential you're gonna have components within the heart totally within the heart not part of
the central nervous system that are going to allow for the the heart to actually those muscle cells
to contract so very unique in terms of having its own pacemaker within the heart now the last and
kind of the more unique of the muscle cells is the smooth muscle cells and you're gonna have these
obviously as the image shows associated with your gastrointestinal portion some forming the walls
of your GI system but also importantly you're going to have smooth muscle cells associated
with blood vessels so particularly in terms of arteries you're gonna have quite a bit of smooth
muscle cells associated with that now if you're looking at the schematic here you can see that
you don't have that typical striation that you have in the skeletal muscle cells as well as the
cardiac muscle cells you do not have the organization of those filaments the myosin and the actin into the
sarcomere so histologically it you don't have that presentation now you very much obviously
have myosin and actin because there's contraction it's just not organized in the same manner now
one of the more unique things about the smooth muscle cells is the amount of extensibility that's
allowed in these so the ability to stretch the smooth muscle cells is quite a bit more
than you have in the skeletal and cardiac muscle cells additionally as similar to the cardiac
muscle cells this is going to be involuntarily controlled so that's kind of an intro in terms
of the types of muscle cells that you're going to encounter throughout your time in this Anatomy
MOOC but we're going to focus on the skeletal muscle cells as we discuss the MSK portion