so now we have an understanding of the the main muscles of the face as well as the neck and the
back so let's move anteriorly and discuss the muscles of the thorax so let's remember what
we're what we're talking about in terms of area so let's talk about the thoracic cage or review
it really quickly so remember we have these ribs how many ribs do we have we have 12 right 12 on
each side and each of these ribs either have their own costal cartilage which is indicated
here in this kind of tan right here or they have a shared costal cartilage so you're gonna have
muscles that are going to be in between in these intercostal spaces right here as well as muscles
superficial to that that are going to play more of a role in terms of the shoulder joint so these
axioappendicular muscles they're going to extend from that thoracic cage all the way to the humerus
so anytime that you cross over the shoulder joint that means that it can have some type of role in
the movement of the shoulder joint so that's what these muscles are doing here so you can
see one of the main ones right here we refer to this as your PEC or your pectoralis major this
is going to have most of its belly right here in terms of the thorax that it's actually going
to attach over here in terms of the humerus so it's not going to play a big role in terms of
movement of the ribs it's going to play a role in terms of movement of the shoulder joint but
I wanted to make sure that we understand that there are these superficial muscles here your
serratus anterior is another example of that so we'll talk more about these muscles when we talk
about the upper limb a little bit later but the main muscles of the thorax are these intercostal
muscles so let's let's get an understanding of where we're at so here our ribs excuse me here
our ribs right here and I told you that we're going to fill in those intercostal spaces with
muscle and you're gonna have three main types of muscles external internal and innermost and they
make sense the external is going to be the most superficial internals right underneath and then
innermost very closely associated the internal intercostal muscles let's talk about fiber so
what we're seeing mostly right here are your external intercostal muscles and you can see
them the direction of their fibers all right think about putting your hands in your pocket
that's the direction that these fibers are going whereas the internal intercostals you can see
are going perpendicular kind of think about getting the hair out of your face that's the
direction of your internal intercostal muscles so it's important that these muscle fibers are
perpendicular to one another to really provide extra extra stability in this region because if
you think about what's right underneath or deep - your thorax you have those lungs right there
so you need that additional protection of those very important organs now these muscles while
they are while they play a big role in terms of increasing just the stability or the tone of
this region they don't play a big role in terms of active movement okay so they're not playing the
big role in terms of flexion extension because they're not attached to the spinal column now
in cases where you have forced inspiration so think take a really deep breath those external
intercostals are going to play a role whereas if you really kind of blow the air out like
you're mad or something like that that's forced expiration and your internal intercostals are
gonna play a role they're typically the the main thing that's causing expiration that's a passive
movement so gravity's really allowing that and really in terms of inspiration that's going to
be the diaphragm muscle which we'll talk about in another section that's going to be the main muscle
there so these are really in cases where you're having you really think about you know breathing
in and breathing out those particular muscles will play a role so these are really the only muscles
that we're going to talk about in terms of the thorax these the main ones we'll move into some
of them the deeper muscles or the cardiac muscles when you get into the cardiorespiratory sequence