hello anatomy friends this is dr alsup and let's finish our discussion of the regional
musculoskeletal uh anatomy of the thorax with the muscles and really our main focus will be
on the intercostal muscles particularly those that are easiest to see which are the in external and
internal intercostals but i do want to note that some muscles are going to be attached
to or covering the thoracic cage and these are really primarily involved in serving or
moving other regions of the body so we will talk a lot about axial appendicular muscles
that will extend from the thoracic cage like you can see here with the pectoralis major
or from this portion portion of the axial skeleton to bones of the upper limb or the appendicular
skeleton so pec major that you can see here pink minor which is deep and the serratus anterior even
are going to have their proximal attachments associated with a thoracic cage and then
attaching to say the scapula or the humerus so really more involved with moving those regions
so we'll get to those when we're talking about the upper limb
but it's not only the axial appendicular scale muscles that you will see there will
be muscles that are attached to the thoracic cage that are also attached to the anterior
lateral abdominal wall the neck and the back so there are lots of different muscles associated
with the thoracic cage but it's really only these intercostal muscles that are intrinsic
in the fact that they both um originate and insert within or on the thoracic cage
so it's these intercostal muscles that are going to occupy those intercostal spaces between the
ribs so here's say rib 2 and rib 3 and then here is your intercostal space right here
and it's really more than just one muscle you'll actually have three different sets of muscles
running in different direct the muscle fibers will run in different directions
the most anterior superficial of these muscles will be the external intercostal muscles
anteriorly as you get closer to the sternal region the muscle fibers are replaced by
external intercostal membrane so you won't really see the muscle belly as much but
this almost tendinous looking region now these muscle fibers will run inferior anteriorly so
it's kind of has this attachment superior superiorly to the inferior border of the rib
above and then it kind of continues down to the superior border of the rib below and these muscles
are most active during inspiration or breathing in or inhalation it is not the muscle of inspiration
that will be the diaphragm but these will be most active and assist in terms of inspiration
the intercostal muscles which you can see here are going to be just deep to the external intercostals
and they the muscle fibers will run in right angles to the external intercostal muscles
and these are weaker in terms of their contraction power than the external intercostals but they will
play a form of a role in terms of expiration or exhalation now you can see one more muscle here
and this is the deepest or the innermost of these and this is the innermost intercostal
it's very similar in terms of the internal intercostal i think the this illustration
kind of makes it seem a bit too vertical the fibers i think go a little bit more this way
but this is base this is essentially the deeper part of the internal intercostals
and really it's only separated from the internal intercostals by neurovasculature the intercostal
neurovasculature which will run in between the innermost and the internal intercostals
okay so that is it in terms of the muscles we're going to cover for the thorax and just
one quick hopefully a softball question but maybe not and if not that's okay too
but i want you to try to think through which of these intercostal muscles that we just discussed
is going to be most active during inspiration is it external innermost or internal and pause
the video if you need to um obviously we're only talking interco intercostal muscles here
but really the key of this stem is most active during inspiration and only one of these will be
will be most notably active and that is the external intercostal the internal is
going to be more in terms of expiration or exhalation and the innermost is really just
kind of an extension or the deeper part of the internal so it will have a similar role
okay so that should uh wrap up our discussion of the thorax please make sure to review the concepts
and the structures that we have discussed and if there's any areas that you need more clarification
or you just want to kind of talk through a concept please feel free to reach out to me with any of
those questions thank you for your time and attention and have a great rest of your day