hello anatomy colleagues this is dr alsup and in this video we will be discussing
the muscles we need to identify in the shoulder brachial plexus and arm session
in the shoulder region the most superficial and largest muscle is the deltoid muscle which
i think of as a cap on the shoulder this is a very coarsely fibered muscle and is dominant
is a very dominant structure in both an anterior like we can see here and a posterior
view so both of these are the deltoid muscle this is an anterior view this is a posterior view
it starts off wider and then it begins to taper off distally
into almost a point actually i would make it go down a little bit further there we go
and it will distally attach on the humerus a little bit uh above mid-shaft region
deep to the deltoid and also in the shoulder region are the rotator cuff muscles
there are three posteriorly located rotator cuff muscles and one that is anteriorly placed and we
will discuss the posterior one first and note that these three muscles all three of these
will have a distal attachment on the greater tubercle which is right here of the humerus
when trying to identify these rotator cuff muscles on the posterior region i first locate
the spine of the scapula which is this right here this bony portion right here recall that
that spine will continue on and it will widen and that's the acromion that we hopefully are getting
familiar with and so knowing where that spine of the scapula is can help you differentiate
the muscles the supraspinatus muscle belly will be located superior to the scapular spine that's
where it gets its name supraspinatus whereas the infraspinatus will be inferior to the spine
see the supraspinatus tendon so here's the muscle belly this whole thing right
here is muscle belly it will continue and it will travel deep to the coracochromial arch
right here in order to reach the greater tuber greater tubercle
and so that relationship right there in terms of that tendon being close to the bone can play
a role in terms of some of the breakdown or damage to the tendon that can occur
the teres minor muscle tends to be the smallest of the rotator cuff muscles and it's located just
inferior to the infraspinatus sometimes it's really difficult to differentiate between the
infraspinatus and the teres minor it often looks like one big muscle but it's going to be just
inferior to the infraspinatus now also in this posterior region is the thick teres major muscle
major meaning it is notably larger than the teres minor the teres major is located between the teres
minor and the latissimus dorsi muscle that we dissected way way back when we were dissecting
the back region note this is the teres major is not a rotator cuff muscle its tendon does
not form part of the cuff that surrounds the shoulder joint but it will move the shoulder
joint when it contracts so it will play some role in terms of movement of the shoulder joint
the anterior rotator cuff muscle is the subscapularis which you can see kind of
deep in this region deep to the subclavian and the axillary artery right here its belly covers
the anterior side of the scapula and of course its distal tendon will form part of the rotator cuff
that's surrounding the shoulder joint you can see that around this region here it's
difficult to tell or difficult to differentiate between what is tendon and what is capsule here
moving now to the arm as we discussed in the last session there is an anterior in a
posterior compartment of the arm when looking at a superficial dissection which is what we have
here of the anterior compartment the most uh prominent muscle is the biceps brachii
the most distinguishable excuse me i can't talk the most distinguishable thing with the biceps
brachii is that the proximal portion has two heads or two proximal tendons you can see these are the
tendons right here here's one that's your short head this is your long head you don't have to
differentiate between the two heads but just for fun and they will come together to share a common
belly and have a common distal attachment you can really see that short head of the
biceps brachii attaching to the deep coracoid process right which is right underneath there
the long head is deeper so you see that it looks like it kind of is hidden underneath
the deltoid muscle it actually will have a portion of its tendon that
travels within the joint cavity of the glenohumeral or shoulder joint
in order to see the other two muscles of the anterior compartment you need to reflect
or remove the biceps brachii muscle which has been done in this dissection this is a deeper
dissection here and you can see the two tendons of the biceps brachii which have been cut
the corco or coracobrachialis muscle is more superiorly placed and it's um going to be
shorter as well so this is the coracobrachialis i like to say correct go but you definitely will
hear coracobrachialis a distinguishing thing regarding this muscle is that the musculocutaneous
nerve which i'm underlining right here will actually pierce the coracobrachialis and it's the
musculocutaneous nerve that is the dominant supply to this compartment this anterior compartment
the brachialis which i'm outlining right now with a few arteries that are getting wrapped
up in there so this is the brachialis it begins around its proximal attachment is around mid shaft
of the humerus and has a very similar belly shape to what we have had with the biceps brachii so key
here is that the brachialis is deep to the biceps brachii so if you can see the coracobrachialis
generally that means that you're deep and so brachialis is going to be on that same plane
the posterior compartment of the arm is a bit easier as there is one main muscle here which
is the dominant and large triceps brachii muscle when looking at a superficial dissection which
is on this side so this is superficial you uh see can only see two of the three heads of the
triceps you can see the long head and you can see the lateral head here you can see and they
kind of come together and they have this common tendon that's going to attach to the olecranon of
the ulna you need to do a deeper dissection which has been done on this side you see
the deltoids been removed you can see some of the lateral or excuse me the long head of the
triceps has been removed as well in order to see the medial head which is going to be more deeply
placed all right most excellent thank you for your time and attention here and hope you are
starting to get familiar with the muscles in this region please reach out if you have any questions