hi let's talk about the posterior triangle of the neck in this video I'll provide you with an
overview of the muscles and structures that are forming the boundaries of the posterior
also known as the lateral triangle of the neck and it's sub triangles we'll also talk about the
high-yield contents of these triangles what the actions of the muscles are and what innervates
those muscles so let's start with a general look at the posterior triangle so the anterior
border of this triangle is the lateral border of the sternocleidomastoid muscle which is here
the posterior border is the anterior or lateral margin of the trapezius muscle which is there and
the inferior border or inferior lateral depending on how the the limb is is the superior margin of
the clavicle so what we have here marking the spot is the posterior cervical triangle that posterior
cervical triangle is divided into the occipital triangle superior lis so there's our occipital
triangle and the subclavian or a mocha color triangle inferior li but we'll take a closer look
at that in a little bit so let's talk a bit about these muscles that are forming the border so the
sternocleidomastoid muscle has a wonderful name it it's name from its attachment points you know
there is the sternum the manubrium of the sternum specifically the the medial third of the clavicle
and then the mastoid process of the temporal bone so this sternocleidomastoid is a very thick strap
that when it contracts with its counterpart on the other side is going to flex the cervical
spine or flex the neck think of the action of drawing your chin down towards your chest
that would be flexion of the c-spine if only one sternocleidomastoid muscle is going to contract
it's going to laterally flex the neck and rotate the face or if you think about the movement of
the chin in the in the contralateral direction of the muscle or the opposite direction of the muscle
the the SCM is innervated through two sources its efferent innervation is cranial nerve 11 or
the accessory nerve it's a ferrant innervation are branches from the ventral primary Ram I of
cervical nerves 2 & 3 it's supplied by blood from the occipital artery the trapezius muscle
I line it here gets its name from its trapezoidal shape so if we were to look at the the posterior
portion of this muscle
kind of looks like that so this would be the superior border of it that would be the inferior
border of it that would be the medial border and the lateral border of it the trapezius
muscle consists of upper middle and then lower fibers or superior middle and inferior fibers
all of these fibers are originating from well up here would be the occipital bone and then
the the spinous processes of various cervical and thoracic vertebrae and then are also attaching to
the spine of the scapula and a little bit of the clavicle as well and so this trapezius muscle if
the if the scapula is that's that's a poorly drawn scapula see if the scapula is is there is going to
be capable of elevating the scapula depressing the scapula retracting the scapula which actually sort
of a medial adduction of it it's also capable of superiorly rotating the glenoid cavity so that's
the shoulder tip so is to work in concert with movement of the upper limb so that that trapezius
muscle can do a lot if the scapula is anchored the the upper fibers of trapezius are capable
of extending the cervical spine so if you think of the action of looking upwards you know where
your chin is elevating that would be extension of the c-spine like the SCM the trapezius muscle
has dual innervation efferent is the accessory nerve just like yeah and a ferrant branches from
the ventral primary Rami of c3 and c4 carry that sensory information back and trapezius is served
with blood through the transverse cervical artery so that's a branch of the thyroid cervical trunk
of the first part of the subclavian artery which we'll discuss in another video breaking up the
posterior triangle is the inferior belly of the omohyoid muscle keep in mind that omohyoid has
two bellies there's a and inferior belly should be there and then there's a superior value there
there's a tendinous intersection with a little bit of a facial sling omohyoid is one of the
infrahyoid muscles so it's going to be one of the muscles that are capable of depressing the
hyoid bone but this inferior belly divides this posterior triangle into the occipital triangle
and the subclavian triangle also known as the Omo-clavicular triangle let's look at some of
the contents that that we can see here so we'll get some of those other labels out of the way
from our anterior next session we have the nerve point of the neck which paradoxically is exiting
or entering through the posterior triangle even though it is serving the anterior neck as well
as parts of the inferior head so we can see there are various cutaneous nerves from that
nerve point of the neck so that nerve point in the neck is up in the occipital triangle we also
have the accessory nerve so the accessory nerve I'll just run parallel to it they're so running
down underneath the SCM accessories coming from the jugular foramen so it's heading this way has
quite a variable course through the the triangles on its way to trapezius one of the ways that that
I like to identify the accessory nerve in this in this milieu of neuro vasculature back here is
that it very frequently has kind of a phone coil appearance to it it looks looks twisty another
content of that posterior triangle specifically the clavicular triangle is the external jugular
vein let me outline that here external jugular vein or ejv crosses the sternocleidomastoid you
can see here I'll just highlight that portion that's crossing the SEM and then it dives
down deep in this clavicular triangle where it eventually joins up with the subclavian vein on
its way to the brachiocephalic vein the external jugular vein is a is a vein that has dual origins
so coming from behind the ear is the posterior auricular vein and then coming down from anterior
to the ear but behind the behind the parotid gland that's the retro mandibular vein retro mandibular
vein has two branches there's an anterior and a posterior and that posterior division of retro
mandibular joins up with posterior auricular to form ejv that anterior division is going to join
up with the facial vein to rain into the internal jugular vein this is ejv is an interesting vein in
that usually one can't see it but sometimes with with issues of the heart and particular right-side
heart failure or even hypertension pulmonary hypertension in particular it can become quite
large and distended so one can I one can can see that that ujv here's a view of well both posterior
and anterior with the sternocleidomastoid muscle reflected and the the one element that that I
wanted to bring to your attention here is we can see some of those c2 and c3 fibers
innervating SCM but we can also see accessory nerve travelling what would be deep - SCM and
on its way to trapezius and we can definitely see it's a little little coiled as it does so look for
that coiled appearance of the accessory nerve so sometimes you may hear the accessory nerve called
the spinal accessory nerve that's the old name for it the new and improved name is the accessory
nerve it's a little more concise in to the point the the accessory nerve actually originates so its
nuclei are in the c-spine you can see those from the cervical spine coming together here and the
nerve comes up through the foramen magnum of the occipital bone so we can see that came here in the
c-spine going in through the foramen magnum and then it comes out the jugular foramen and when it
comes out the jugular foramen it is accompanied by cranial nerve nine which is glossopharyngeal
cranial nerve 10 which is Vagus itself and that's where the ijv originates so a lot is
coming through those jugular foramen ah and then you can see it descending down the neck under SDM
and on its way to trapezius and we can see here are some contributions from c2 and c3 and c4 to
provide the efferent innervation from trapezius in sternocleidomastoid so contributions from c2
and c3 are the afferent for SEM contributions from c3 and c4 are the afferent four trapezius but the
efferent or the motor is the accessory nerve cranial nerve 11 so let's round this up with a
question to test your retention and understanding so a patient is suffering pulmonary hypertension
and right-sided heart failure so what's happening here is that there is increased resistance for the
pulmonary arteries that are delivering blood to the lungs from the right ventricle and as a
result of that the right side of the heart the right ventricle is beginning to enlarge it's
hypertrophied because the muscle has been working harder and when muscles work harder they enlarge
or hypertrophy and as a result of that blood is flowing slower to and through the right side of
the heart so there's diminished capacity of blood which visibly distended veins may be a sign of
this right-sided heart failure a external jugular veins B internal jugular veins C subclavian veins
well the truth is all of these veins can become distended as a result of pulmonary hypertension
and right-sided heart failure but it is the external jugular veins that are going to be the
most visible recall the relationship between the external jugular veins and the sternocleidomastoid
muscle so external jugular veins cross over the SCM in the neck and it's this region that makes
the ejv so very visible if there is any element of distinction to it thank you for your time