hello anatomy friends this is dr alsup and in this video we will be talking through some of
the specifics of the main anterior thorax muscles and when i say thorax thorax or think i want you
to think between the neck and the abdomen so that area there that has the rib cage and part of the
vertebral column these three muscles are going to be the two pectoralis muscles major and minor
as well as serratus anterior so let's start with pectoralis major muscle which is this large fan
shaped muscle which has two proximal attachments or we like to call these two heads of the muscle
you will have a clavicular head which you can see here it is going to as its name would suggest
attached to the clavicle and a sternocostal head which you can see is the larger one
and this will attach to the sternum aka that breast bone and the costal cartilages which
are how the ribs attach to the sternum the distal attachment is on the proximal humerus so you can't
really see the the bone here but you can see that it is heading towards the arm so it is going to
attach specifically to the crest of the greater tubercle of the humerus so looking at these
attachment points you can see that the pectoralis major muscle will cross the glenohumeral joint
which would be about here and so since it crosses the glenohumeral the shoulder joint when
it contracts it can directly affect some of the actions that occur at the shoulder joint speaking
of actions the pectoralis major muscle can do quite a lot but it is dependent on which part of
the muscle is contracting because the clavicular and the sternocostal heads can actually contract
simultaneously or separately so when contracting at the same time this will cause the shoulder
joint or arm to adduct all right so just think this muscle gets shorter and it would lead the arm
to adduct or move more towards the midline it will also or it can also medially rotate
the shoulder region so that means that anterior portion of the arm will kind of rotate medially
and there are some excellent videos in the blue link resources showing these actions and the other
major joints of the body so if you want to kind of look at what that looks like i'd highly recommend
those and it'll be a link in the learning objective text when only this clavicular head
contracts so when it contracts by itself or alone it can flex the shoulder joint or bring the
arm anteriorly kind of kind of towards us not down sorry i should say it's more it's kind of
hard to to draw that because it's coming anteriorly and the in the sagittal plane
whereas the opposite happens when the sternocostal head contracts alone which
will extend the shoulder moving it back towards anatomical position from that flexed position
or past anatomical position in a more posterior direction so kind of move your arm anteriorly
that's flexion and if you move your arm posteriorly that's going to be extension
all right now let's discuss the neurovascular supply of pectoralis major and both the lateral
and medial pectoral nerves will provide uh efferent and afferent innervation for this muscle
so you can see the lateral pectoral nerve here i'm outlining it here and the medial is going to be
here in here you can see it piercing through peg minor usually just one nerve will innervate
a muscle but in cases where there's a larger muscle like what we have with pectoralis major
there may be two nerves so that that's the case here and both of these nerves will originate
from the brachial plexus more to come on the brachial plexus much much more in upcoming blocks
arterial supply will be from the thoracoacromial artery
and this is actually quite a large artery i'm circling it right here and it has lots of branches
and some of those will head towards the pectoralis major as well as the minor to provide blood
and this is a branch of the axillary artery which is an important major artery of the arm
since this muscle is so large it has a few important anatomical or clinical relationships
it will form the anterior wall of the axilla and we like to kind of refer to the axle as the armpit
region additionally the investing deep fascia that will surround the muscle is called pectoral
fascia and this muscle and its associated fascia is very closely associated with the breast
which is just anterior to the pectoralis major and its fascia so there if there's any type of
breast pathology or surgery in that region that needs to be done this muscle or its fascia or its
neurovasculature may be affected or the muscle may need to be resected or moved to get to some
of the the deeper structures around there all right moving on to the pectoralis minor muscle
which is just deep to the much larger pectoralis major so if pectoralis major was here it'd be kind
of like right around this region going this way and it would completely cover the pectoralis minor
the muscle's proximal attachments are on the anterior surfaces of ribs three through five
it's odd looking three there and the distal attachment is on the scapula specifically
the coracoid process so you can see here that it does not cross the shoulder joint and the shoulder
joint would be right here so it does not cross the shoulder joint so it will not have a direct effect
on the shoulder joint but it will certainly have an indirect effect
instead the pectoralis minor muscle will affect the scapulo thoracic
joint and anytime you see something in quotes like i have here that should raise your eyebrows and um
so what is the scapulothoracic joint it's probably not one you've heard of before well it's
not a typical synovial joint like the shoulder the elbow or the wrist instead what we're describing
here is more the movements of the scapula on the thoracic cage so the thoracic cage is the the
rib cage basically connected to the sternum and the vertebrae and so it's basically how
that scapula will move in comparison to the thorax and you can see an image that kind of
shows a breakdown of the different types of movements that can occur with of the scapula
and it's these movements um that will also help facilitate a full range of motion at the shoulder
joint so you need that scapula to move in order to have that full range of motion say get your
arm all the way you know pointing all the way up that you need the scapula to move as well
specifically pectoralis minor muscle will play a big role in overall stabilization of the scapula
and what i mean here is that it will keep the scapula kind of locked down or in place while
other upper limb joints move so that's what we mean by stabilization but when more forceful
contracting of the pectoralis minor muscle occurs this can also play a role in terms of protraction
or moving that scapula more anteriorly and laterally protraction is sometimes referred to
as abduction of the scapula the neurovasculature is very similar to that of the pectoralis major
muscle the only substantial difference is that only the medial pectoral nerve will innervate
pec minor and a very notable relationship is that additionally this pec the medial pectoral nerve
will actually pierce directly through the pectoralis minor muscle as it heads to the
more superficial pectoralis major so if you had hypertrophy of the pectoralis minor muscle
to a very large extent it could feasibly pinch on the medial pectoral nerve
another important relationship is that the pectoralis minor muscle will subdivide the
axillary artery which is right here and it will subdivide it into three parts so you can see
pec minor muscles tendon right here it would kind of continue this way over here to the ribs
and what it will do is you can see that the belly would be located kind of right here
and the axillary artery will be described based on its relationship to the pectoralis minor so
is this portion would be medial to it that would be the first part this would be the second part
that would be deep to pec minor and then this part lateral to it would be the third part don't worry
so much about first second and third part we'll come back to that later on in the musculoskeletal
content but this is an important relationship an anatomical relationship of pectoralis minor
lastly we have the serratus anterior muscle which is going to lie over a fairly substantial part of
the lateral part of the thorax and it has this very sawtooth appearance which is actually where
it gets its name the serrated type of appearance with these little slips of muscle which are
actually not that little they're actually fairly robust and this muscle will approximately attach
to the superior most rib eight ribs so ribs one through eight and it will distally attach
to a large portion or the majority of this anterior portion of the scapula so this is
posterior should be on this anterior part so again this muscle is not crossing the shoulder joint
and will more directly affect the movement of the scapula serratus anterior is actually an extremely
powerful muscle and is a very powerful protractor of the scapula more so than pectoralis minor so
a boxer may have a hypertrophy serratus anterior muscle so it may be more built up because punching
involves protraction of the scapula so kind of try to punch your arm out and that scapula will be
moving kind of lateral and anterior the more inferior portions of serratus anterior will rotate
the glenoid cavity which is the part that attaches or that articulates with the humerus
it will rotate that glenoid cavity of the scapula upwards and this will really allow the arm to be
able to be raised above the shoulder so this is what i'm talking about how pectoralis minor
and serratus anterior are directly affecting the scapula but it will play an indirect role
in terms of the glenohumeral joint it can also play a role in overall stability of the scapula
serratus anterior is innervated by the long thoracic nerve which is also a branch of the
brachial plexus and this nerve is very uniquely placed so most nerves are going to be located deep
to the muscle it innervates but this is not the case for the lung thoracic which runs right down
the superficial portion of the muscle and so just thinking about this this would make this nerve
more susceptible to injury think of a stabbing injury to the side of the body or that side of
the thorax but also in surgeries around this region or around the axillary region so like an
axillary lymphatic node dissection or surgery that could directly affect or cause a lesion or a kind
of nick to the long thoracic nerve and thus that would affect the actions of the serratus anterior
and this would lead to what is called a wing a winged scapula which is going to
cause the scapula to be visibly displaced posterior laterally supposedly residualing
wings and this can greatly affect scapular motion but also shoulder joint movement and this
anatom this i have a star here i'm going to put another star here and maybe another star here
these this anatomical clinical relationship of that long thoracic nerve um causing or a lesion
of the long thoracic nerve causing what's referred to as a winged scapula is one of those things that
very often come up not only on your upcoming assessments but also some of those step tests
that i'm sure you may have heard of so this is one of those classic anatomical clinical relationships
alright we have made it to the end into our summary slide these are those really big
picture high yield concepts we want you to walk away with as you review please always
feel free to reach out with any questions and thank you for your time and attention