hello all this is dr alsup and in this video we're going to begin our discussion on the muscles
of the upper limb as always we're going to start proximally and move our way distally so our first
set of muscles that we're going to discuss are those axioappendicular muscles so those
uh muscles that will have some form of attachment on the thorax in addition to either the pectoral
girdle or the shoulder or the humerus and then lastly we'll talk about those short intrinsic
shoulder muscles so you can see um that our major muscles are going to be pec major pectoralis minor
serratus anterior our shoulder cap muscle the deltoid and lastly the rotator cuff muscles
so again just a reminder of what we mean by axio appendicular muscles uh these are going to have
their muscle bellies on the thorax meaning that they'll have a proximal attachment on the thorax
and then those distal insertions or attachments will either be on the scapula or the humerus
and depending on whether it is attached on the scapula
or the humerus means that either only moving the scapula or this means that this could be
moving the shoulder joint so we'll talk about those major muscles as well they can also play a
role in terms of moving portions of the thorax as well in terms of a reverse action motion
okay so let's start with the big one pectoralis
major and this is kind of in the breast region so just deep to the breast you will have two heads
you will have the clavicular head which you can see right here and you can see it attaching on
that clavicle and then you have the larger more fan shaped sternocostal head and just kind of
working through where this attaches proximally you have the sternum and costal cartilages and then
both of these heads will kind of come together in a common tendon to attach on the humerus meaning
that these this muscle will directly affect the shoulder joint in terms of his actions
and so when both heads are contracting both the clavicular and the sternocostal
this will play a role in terms of adduction or moving that shoulder or the arm back towards
the midline as well as medial rotation so think of this anterior portion of the arm medially rotating
but interestingly when the two different heads contract independently they can be antagonistic
to one another so that clavicular head if it's contracting by itself will cause the arm to flex
meaning i think of the arm moving anteriorly whereas the sternocostal head when it contracts
by itself or independently it can't extend the shoulder particularly from that flex
position so it is cool that we have one muscle that can be antagonistic to
itself depending on what fibers are going to attack or what fibers are contracting
we'll have another muscle like that that we'll talk about in this video
deep to the pectoralis major so here's pectoralis major that has been reflected
you will have the pectoralis minor and as its name would suggest it will be minor or
smaller to the pectoralis major you cannot see pec minor until pec major has been reflected
it will have a distal attachment on the coracoid process as you can see here of the scapula which
means that it does not cross the shoulder joint so it will only affect the actions of the scapula
and it will play a role in terms of protraction of the scapula as well and we'll talk about
what that action is in a moment but really kind of the main role of pectoralis minor
is to stabilize the scapula um meaning not really allowing the scapula to move to allow the shoulder
joint to really do some more purposeful movements because the scapula is kind of stuck in place
the last axio appendicular muscle we're going to discuss is the serratus anterior and it is named
due to its kind of sawtooth appearance so you'll have these little slips of muscles
attaching on the ribs and then it will have an attachment to the anterior portion
of the scapula kind of that medial border as well and this is a pretty powerful muscle
it will cause protraction of the scapula because it is not crossing this shoulder joint it is going
to directly affect the scapular movements in protraction you kind of think of moving
the scapula particularly that medial border of the scapula away from midline all right
so think of kind of when you put your arm out in front of you or if you kind of punch
right out in front of you anteriorly that scapula is going to move away from the midline
a lot of times you'll hear this muscle referred to as the boxer's muscle because they're going
to utilize it so much in order to get this kind of forceful kind of punching movement
now there's something unique about the serratus anterior that i really want to
make sure that we understand when we're talking about neurovascular bundles and the innervation
of muscles typically the nerve that will innervate the muscle will enter the muscle kind of
deep to the muscular belly all right so almost every neurovascular bundle you will see
will be coming in deep to the muscle and that plays a role in terms of added protection
to that neurovascular bundle now what is unique about the serratus anterior and its innervation
is that its muscle or its nerve the long thoracic nerve will enter and innervate the muscle
superficially so here's the serratus anterior you can kind of think it would be like right
about here running down this region so that is very unique in terms of how that innervation
is organized in comparison to the muscle belly and you can kind of think about if you had some
type of injury say some type of like stabbing um right to the side right there or some type
of surgery in this region maybe to remove some lymph nodes you could directly affect and kind
of nick that long thoracic nerve as it's so superficial right there and that is referred
to as um paralysis of the serratus anterior but more commonly you will hear this referred
to as a winged scapula because supposedly that scapula will look kind of like wings
and you can see this medial border of the scapula on the injured side will kind of
move posterior laterally and kind of project and really it will project posteriorly and so it'll
become much more obvious than on the other side and so really this is most commonly caused by
injury to that long thoracic nerve which will lead to paralysis or weakening of the serratus anterior
okay now moving into the intrinsic shoulder muscles these tend to be short and they are going
to have their proximal attachments on the scapula and they will have their distal attachments on
the humerus so meaning that they will cross the glenohumeral joint and play a big role in terms of
movements of the glenohumeral joint and also very importantly stability of the glenohumeral
joint so we'll start with the big one the deltoid the deltoid is the shoulder cap muscle
if you think of the muscle that's sitting right on top of your shoulder that is the deltoid
it is a big muscle it is a very robust muscle the the fibers are very robust in this region
and it's going to have three different parts you'll have the clavicular part the acromial part
and the spinal part sometimes you hear these as anterior middle and posterior
but it really is kind of giving you an idea of their basic organizations of how they're organized
and the this is kind of similar to what you had in the pectoralis major where dependent on
which fibers are contracting you can have very different movements that occur
and they can be antagonistic to one another so you can have flexion and extension so flexion would
be that clavicular extension would be the spinal contracting independently same thing with medial
and lateral rotation now i'm not going to have you memorize which fibers cause which action like
i did with pec major just because there's a lot more actions here but i do want you to note that
dependent on which fibers are contracting this muscle can be antagonistic to itself
so so it can't flex extend it can medial and laterally rotate but really kind of the money
action when we're talking about the deltoid muscle and typically its most powerful action will be
abduction and so a lot of times you hear that this acromial part will play the biggest role
in abduction but all three uh parts are really contracting for abduction to occur so abduction
is really moving that that arm or moving the shoulder joint away from the midline and this
muscle is going to be innervated by the axillary nerve which is one of the terminal branches of
the brachial plexus so that axillary nerve if you recall is going to move around the
surgical neck of the humerus so if you have a fracture to that surgical neck you could
directly affect the axillary nerve which would affect these actions we're just talking about
okay and then deep to the deltoid muscle you will have the rotator cuff muscles and we talked about
the rotator cuff muscles when we were talking about the shoulder joint or the glenohumeral joint
as it is these muscles are extremely important in terms of the stability of the glenohumeral
joint so it'll form that almost complete cuff around the shoulder joint and so really
we're going to talk about some of the separate movements that these muscles will play a role in
but when you talk about all four of them together really one of the major functions of these four
muscles are to help stabilize and keep the head of the humerus us articulated with the glenoid fossa
there are four or they're four in all rotator cuff muscles but there are three rotator cuff muscles
that are going to be located posterior on the scapula in terms of their proximal attachments
you will have the supraspinatus which is above the spine of the scapula
the infraspinatus and the teres minor right here so these are three of the four rotator
cuff muscles all three of these muscles will have their distal attachment on the greater tubercle
of the humerus and that's why the greater tubercle is greater than the lesser tubercle because it has
three muscles attaching there rather than the one there are going to be different actions that are
associated with these muscles the supraspinatus or that most superior one will help initiate
abduction of the shoulder so about that first 15 degrees of the action of abduction is going
to be caused by the contraction supraspinatus and then from there deltoid muscle takes over
the infra and infraspinatus and teres minor are going to be very important lateral rotators
of the shoulder so kind of thinking of moving that anterior portion laterally
and then lastly the the fourth rotator cuff muscle is the subscapularis and this is the only one that
will be located anterior on the scapula so it's a it's a rather large muscle so this
is the anterior surface of the scapula just deep to the subscapularis and you can see it's pretty
much taking up almost all of the space right here and it will have its distal attachment on
the lesser tubercle and it will be a very powerful medial rotator of the shoulder okay so that should
cover us in terms of the muscles but before we leave i can't not talk about rotator cuff injuries
because you've probably heard of rotator cuff injuries and just you may known somebody who had
a rotator cuff injury you may have heard it in terms of some type of a sporting event
and what this is is kind of a complex of many many different types of things that can occur
but what is going to be most common is some type of tear or rupture or damage to that
muscular tendinous rotator cuff so that portion of the tenderness portion that is going to attach
and surround that the shoulder joint underneath here and anytime that you have any type of injury
or weakening of this rotator cuff this is going to be a cause of increased instability of the
glenohumeral joint because recall that rotator cuff is so important in terms of the stability
the most commonly injured or damaged will be the tendon of the supraspinatus and really i would
have this tendon a little bit further over here i think this is showing the muscle belly a little
too long because really that tendon can rub up against with increased friction the the
acromioclavicular joint region or these bony portions particularly if the arm is abducted or
flexed you know fully think about abducting your arm above your head you know thinking of
that particular in or type of movement you could see that tendon could feasibly pinch or kind of
rub up against the bones in this region making this tendon one of the most commonly injured
recall also that we had a bursa up there that subacromial or subdeltoid bursa
and so that inflammation in that region of that bursa or any of the bursa in these regions
uh could lead to bursitis or pain associated with the rotator cuff general regions
so not an uncommon thing that occurs this can happen due to overuse of this region
say like in an athlete a pitcher could be more susceptible to this type of injury but
also with increased age oftentimes you will hear rotator cuff injury frequencies increasing as well
okay so that should finish us in terms of the muscles that we are going to discuss in the axio
appendicular region as well as those intrinsic shoulder muscles so one a fairly important area
i want to make sure we review so damage to the axillary nerve may affect all of the following
actions except which of the following so kind of keys here are going to be axillary nerve
is damaged and we're looking at separate types of actions and so all of these are shoulder joint
so that should be helpful in terms of okay we need to be thinking shoulder joint region and
you need to think about which um which muscles are going to be innervated by the axillary nerve now
the teres minor is also innervated by the axillary nerve i'm not going to have you memorize that one
and terry's minor as you recall is going to be important in terms of lateral rotation that's not
on here so no worries there what's the other major muscle that is innervated by the axillary nerve
hopefully you recall the shoulder cap muscle or your deltoid muscle is going to be innervated by
the axillary nerve so we've got that part down we've we kind of had a second order question we
needed to know what the axillary nerve innervated so we know the deltoid now we need to understand
what are the actions of the deltoid muscle and recall that the deltoid muscle dependent on which
muscle or which muscle fibers are contracting can do quite a bit abduction is definitely one of the
major actions of the deltoid so this is not right adduction i don't really remember that one quite
as much and then remember that depending on which muscle fibers are contracting there's a lot of
actions that could occur that are antagonistic so flexion and extension
are feasible medial and lateral rotation are also possible at with contraction of the deltoid muscle
so it's really this adduction of the shoulder joint is which is basically the only action
that the deltoid muscle will not play a role role in so adduction is going to be the correct answer
here okay so make sure that you review these muscles and kind of the major things that we
reviewed in the lecture if it's not covered in the lecture it's not that it's not important
it's just not going to be something that you need to make sure you recall for the assessment
thanks for your time and attention here and have a great rest of your day