Let's discuss axioappendicular muscles and we broached the subject we were talking about
muscles at the thorax specifically the anterior muscles now these muscles we are discussing
here because they're going to play a bigger role in terms of the shoulder joint some of
these muscles attach directly to the scapula and will play a role in terms of movement of
the scapula but more of them are going to play a role in terms of the movement of the glenohumeral
joint so moving the pectoral girdle in addition to the glenohumeral and when we're
talking anteriorly the main muscles that we're talking about are your pectoralis muscles and
we probably all heard of these and when we think of the pectoralis muscles we're mainly thinking
above about the pectoralis major and deep to the pectoralis major is the PEC minor now
on the side you're going to have your serratus anterior muscles and this is a really unique
muscle in terms of its innervation so let's start with pectoralis major this is going to
have two different heads associated with it you're gonna have a clavicular head
and a sternocostal head so attached to the sternum and the costal cartilages both heads
when they're contracting are going to be very important in terms of adduction or bringing
your the shoulder joint back to anatomical position as well as medial rotation of the
shoulder so this you have to have both muscles or both heads contracting but they can contract
individually and they'll actually be antagonistic to one another so the clavicular head is going to
flex whereas the sternocostal head can extend so that's very unique not all muscles can actually
do opposite motions but these since there are two different heads can so you can see here you
have the nipple in this region you have your deltoid right here and this is your PEC major
now like I said pectoralis minor is going to be deep to major so you can see your major has been
reflected here and the much smaller pectoralis minor here so this one doesn't actually play
a role in terms of the glenohumeral joint it's going to play a very important role in terms of
stabilizing scapulae specifically in movements allowing for the higher range of motion of the
glenohumeral and keeping that scapula where it needs to be and this particular muscle has an
attachment to that coracoid process remember on the anterior side of the scapula the serratus
anterior and that this is one of my favorite muscles I think it's a very uniquely shaped you
can see it's the sawtooth appearance here this is your serratus anterior now this is a very
unique muscle and the fact that the nerve which you can't see in this image but I kind of show
you where it would be it's actually gonna run superficial to the muscle okay so most nerves
you're gonna see on the deep side of the muscle this is not true for the serratus anterior it's
going to be on the superficial side so if you have a direct blow to this side or some type of stabbing
wound in this area it can directly damage that long thoracic nerve and cause what we refer to as
a winged scapula or the scapula will kind of move posteriorly out of the way okay so if you think
of protraction kind of putting the scapula out like that if you're doing a push up this is where the
serratus anterior is really playing a big role okay so those are the main anterior muscles let's
move on the posterior side and it's quite a bit more complex in this region you have three main
categories of region you have superficial and these are going to be the larger of the muscles
your trapezius and your latissimus dorsi your deep which are not going to go into too much
detail here they don't play a big role in terms of the actions but these muscles are referred
to as the rhomboids you have a rhomboid major and a rhomboid minor and your levator scapulae
and then muscles associated with the intrinsic shoulder so playing an important role in terms
of not only the actions of the shoulder joint but also the stability of the shoulder joint
and we all have heard of the deltoid that's the muscle that kind of cap on top of your shoulder
and then your rotator cuff muscles which are forming kind of a very important protection
on either side of the shoulder joint so let's start with the superficial muscles now we
know we've talked about trapezius before but a real quick review it's gonna be this trapezoid
shaped muscle here it's not going to play a role directly in terms of the shoulder joint it's
really playing a role in terms of the scapula so similar to the pectoralis minor in terms of
stabilization as you move inferiorly you have this bigger fan shaped muscle or your latissimus
dorsi this does actually attach to the humerus so crossing the glenohumeral joint and can play
a role in terms of extension adduction and medial rotation so extension adduction and
medial rotation a lot of actions that come into play when you're swimming so oftentimes you hear
this muscle referred to as the swimmer's muscle so anytime you look at a swimmer they'll have
very developed latissimus dorsi muscles the deltoid muscle is going to be that cap that
you can see right here on the top a very thick very robust muscle is an area of intramuscular
injection so if you think of where you get your shots oftentimes it's in the deltoid this the
main role of the deltoid muscle is abduction it is going to do the majority of abduction of the
shoulder joint so think about moving your arm this way but different areas of the deltoid so
different muscle fibers of the deltoid can also play a role in terms of flexion and extension of
the shoulder joint it's going to be innervated by one of the terminal branches of the brachial
plexus your axillary nerve then all the rest the rotator cuff muscles we talked quite a bit about
the rotator cuff muscles when we discuss the specifics of the glenohumeral joint but let's
talk a little bit more about the actions that can occur at these joints so if you're talking about
all the posterior muscles here you have your supraspinatus infraspinatus and teres minor so
let's look at these here supraspinatus is above the scapular spine infraspinatus is below since
the names make sense and then underneath here you have the teres minor these are all going
to attach on that greater tubercle of the humerus that's why the greater tubercle is larger than the
lesser tubercle supraspinatus is going to initiate and I should have put this in here it's going to
initiate abduction so allowing for the movement of abduction to start and then deltoid the deltoid
muscle will take over whereas infraspinatus and teres minor are gonna play a role in terms
of lateral rotation of the shoulder joint if you were to flip on the other side now we're looking
at an anterior view you have your subscapularis muscle which is quite a large muscle it's pretty
much taking up the whole space right here this is going to attach on the lesser tubercle of the
humerus it's the only muscle that attaches here that's why the lesser tubercle is going to be
smaller and as opposed to the infraspinatus and the teres minor subscapularis is going to be a
medial rotator of the shoulder so you've heard of rotator cuff muscles probably before this is an
area that's often damaged specifically or more commonly you're gonna have your supraspinatus
tendon being damaged so let's talk about why that would be so let's find supraspinatus here
you're gonna see it located here the tendon is going to be attaching to the greater tubercle
and if you think about you have some bones right here specifically your acromion process you have
your coracoid process here you have a very strong ligament right here and in actions of circumduction
it's going to get pinched often so if you are an individual that circumducts your arm quite a
bit so if you think of a baseball pitcher you're using that area quite a bit there's going to be
friction and that can lead to damage or a tear in terms of the supraspinatus tendon so that's
why you're gonna have this being the most commonly injured of the specific tendons of the shoulder of
the rotator cuff if you have damage here this can cause quite a bit of instability because this is
really the main force in terms of protecting your glenohumeral joint and recall and we've discussed
this in terms of the joints it's in this kind of ring around but then you have this weak area
inferiorly so when you had that dislocation it'll move inferiorly and then typically anteriorly