okay hello anatomy friends let us discuss the shoulder muscles or the muscles that are very
closely associated with the shoulder joint and we're gonna start with a posterior view here
which you can see fairly clearly and let's talk about why we know that this is a posterior view
because we're always trying to get these hints to help us get organized when we're looking at
something like this so for me the few things that really point out that I'm looking at a posterior
view so real quick I'm going to write that out once again you know my handwriting is better
than this in real life but I'm doing my best here so you can see a little bit of bone right
here that is going to be that scapular spine if it extends further this way you're getting
towards a chrome Ian so remember that scapular spine is always always posterior so a good hint
we're looking posterior additionally over here I can see your triceps brachii triceps brachii is
going to be that expanse of three heads in the posterior portion of the arm and that's always
going to be posterior and since you have that scapular spine and your triceps you know you're
looking at a posterior view so let's try to tell which muscles were looking at here specifically
the muscles that are associated with the shoulder region and this large kind of cap like muscle is
your deltoid our good friend the deltoid muscle it is usually pretty easy to tell you're looking
at the deltoid like I said I always think of it as kind of the cap of the shoulder kind of sits right
on top of it it's going to help form that rounded contour that we're all used to seeing through the
skin it is going to have its proximal attachments on the lateral clavicle which you can't see here
we'll see in an anterior view the acromion as well as the spine of the scapula which you can see here
and the osteological landmark that we do want you to know in terms of where it inserts or has it's
distal attachment on the deltoid tuberosity of the humerus and you can see about where that would be
located and that's on that lateral portion of the shaft of the humerus so the deltoid tuberosity
would be right about here ish as we have discussed in many many sessions before we know the deltoid
is going to be innervated by the axillary nerve now you you can see a little bit how they're kind
of separate fibers associated with the deltoid muscle and this helps form the different parts
of the deltoid you're gonna have a clavicular part which you can't see in this posterior view
right here would be the acromial portion of the deltoid and back here in the posterior
region would be the spinal portion of the deltoid these three parts can act independently and when
all three parts act together or contract at the same time that's really where you're gonna get
that powerful aBduction action that occurs with the deltoid okay now let's see which rotator cuff
muscles we can see in this posterior view and I always go back to that scapular spine because
that helps me to get organized in this region you can see above or superior to the scapular
spine is the supraspinatus so the supraspinatus muscle belly you can see fairly nicely here it is
sitting right on right within that supraspinous fossa as its proximal attachment and then it
will make its way to the greater tubercle in order to have its distal attachment and as
we discussed the supraspinatus is going to be the most commonly injured rotator cuff muscle
particularly its tendon which we've seen in some of the other dissection supplements now underneath
or inferior to the scapular spine is going to be the infraspinatus and it's going to be this kind
of larger expanse of muscle underneath here it is sitting in the infraspinous fossa of the posterior
scapula which you can see here and it also will have a distal attachment on the greater tubercle
now this one is from me then usually the most difficult one to tell and that is the teres
minor and as its name would suggest it is going to be smaller than the teres major and that
is certainly the case as you can see on this particular specimen in certain dissections in
certain individuals it is really difficult to tell the difference between the infraspinatus and the
teres minor muscle we would have to have a nice clear division between the muscles like we do in
this particular image for you to know that you're looking at the m4 spinous which will always be
superior to the teres minor and the teres minor will always be superior to the teres
major so to review these muscles that are in this region this is going to be the infraspinatus the
teres minor is going to be the smallest of these muscles still a rotator cuff muscle and then we
have the larger teres major right here which is not a rotator cuff muscle but a very dominant
muscle when you're looking at this posterior view so it's kind of sitting at this attaching here at
this inferior angle of the scapula and that's the inferior angle right about here and it will end
up inserting or having a sadistic attachment on the crest of the lesser tubercle so not quite on
the lesser tubercle like the subscapularis but on the crest that's a little bit distal to the
lesser tubercle and this is going to be visible or palpable in the posterior axillary region all
right this is still a posterior view and you may remember this particular image from when
we did the the early back dissections before we did the laminectomy x' and what i want you to
focus on here is the latissimus dorsi muscle or the latissimus dorsi muscle it's this expansive
muscle so the majority of the muscle belly is going to be based in a wide attachment in the back
region so it has attachment on spinous processes the thoracolumbar fascia if you remember this the
iliac crest so it goes all the way down to this region but it's important to note that it's distal
attachment or its insertion is on the humerus in the intertubercular sulcus of the humerus of
that means that it crosses the shoulder joint and therefore it will act on the shoulder joint so it
plays a role in terms of medial rotation ad or adduction and extension so while we think about
it oftentimes in in regards to the back because that's where the muscle belly is mostly located
it does cross the shoulder joint therefore it will act on the shoulder joint and this isn't
on your list of structures but let's remember our good friend the trapezius over here because
it is going to be very closely related to the shoulder region as well it inserts or has it's
distal attachment on the scapula so to play a role role in terms of scapular movements and so
really close to the deltoid which you can see here all right one more posterior view here as
a review just because we want to all make sure we're on the same page also in this particular
image you can see the tendons a little better so latissimus dorsi let's start with that one you can
see here is latissimus dorsi here it is going to be inferior to your Teri's major muscle and really
I think it's usually pretty easy to tell the difference between teres major and what system
is dorsi because you can see with this myth excuse me latissimus dorsi is going to be more expansive
but you can see how it's heading towards the humerus for its distal attachment teres major
is this large robust muscle that is going to be inferior to the Teres minor and this particular
specimen has a really nice clear division between the teres minor and the infraspinatus and a lot of
the ligaments and tendons attachments because the deltoid muscle has been completely removed in this
particular specimen you can see that scapular spine really nicely which would be occluded
in some areas because of the deltoid if it were there now following the teres minor you can see
its tendon heading over to help form that muscular tenderness rotator cuff same thing here with the
infraspinatus and then superior to the scapular spine you have your supraspinatus muscle belly
and you cannot see the tendon quite as well but it's going to be around this region here going
through the tunnel formed by the crack of acromial arch and lastly this is looking at an anterior
view and once again the deltoid muscle has been removed it would be kind of sitting right on top
of the glenohumeral joint region as well as the acromioclavicular region and you can see right
here because we've had to kind of laterally rotate on this particular specimen in order to see the
suprascapular muscle belly which is going to be located on the anterior portion of the scapula so
sitting right within the subscapular fossa on the anterior scapula and it will insert on the lesser
tubercle or we'll have a distal attachment on the lesser tubercle which is right about here ish
maybe a little bit more inferior it is the only one remember that it's going to have its distal
attachment on the lesser tubercle all the rest of the rotator cuff muscles are going to be on the
greater tubercle and so you can see how its tendon is really helping to reinforce this anterior
portion of the joint capsule for the glenohumeral joint region so if you're looking at an anterior
view and you know you're looking at an anterior view for a few reasons here's your clavicle
clavicle is always going to be anterior you can kind of see a little bit of your brachialis muscle
right here you can see your subclavian artery around this region as well which will transition
into the axillary artery so you know that's gonna be a more anterior they placed vasculature so this
is an anterior view here alright so those are the muscles of the shoulder region I think that
of muscles like compared to the forearm this region I think is particularly or one of the
easier ones to be able to identify the difference between the muscles I think probably the most
difficult one is telling the difference between the infraspinatus and excuse me the teres minor in
the infraspinatus just remember infraspinatus is going to be the larger one it's gonna be directly
underneath the scapular spine teres minor will be inferior to the infraspinatus and smaller
and certainly smaller than the teres major and we would have to have a nice division between
the muscle fibers in order for you to be able to identify the posterior muscles of the shoulder
region alright thank you for your attention I hope this has helped in terms of being able to identify
the muscles in the shoulder region as always please feel free to reach out to me and any of
my Anatomy colleagues we'd love to talk shoulder muscles please have a great rest of your day