hi let's talk about the nerves of the posterior neck so with respect to the nerves in this area
there are a few recurring themes that we're going to revisit continually throughout throughout this
course one of the major themes that will repeat is that of the vagus nerve or cranial nerve 10
the vagus nerve exits from the jugular foramen it is bound up with the internal carotid and the
internal jugular vein by condensations of deep cervical fascia called the carotid sheath so
within the carotid sheath we were able to see a couple of major elements and they're pulled
apart here so here we have the internal carotid artery there's the external carotid and they meet
the common carotid and here we have the internal jugular vein and descending down here is the vagus
nerve or cranial nerve 10 let's erase all of these keep in mind that these elements have been pulled
apart for the sake of being able to see that the deeper elements so normally the the common
carotid and the internal jugular are approximate to one another and then the the vagus is sort of
intermediate and posterior to these two elements so let's let's talk a little bit about the the
vagus nerve and some of the branches that we'll see from the vagus so this right here is the
lower edge of the parotid gland and if we're to look deep and beyond there we can see the the
bulk of the vagus nerve traveling down and this would be within the the carotid sheath and before
it descends too far we see this bifurcation there that bifurcation is the superior laryngeal nerve
and so the superior laryngeal nerve as its name would suggest serves the larynx there are two
branches to it and we can see there's one branch that's heading this way this a little bit larger
on this particular donor it continues there and it then pairs up with an artery branch and this would
be the superior laryngeal artery and the to dive through a little hiatus in the thyrohyoid membrane
which is located between the hyoid bone and the thyroid cartilage here and they they serve the the
deeper parts of the larynx so that would be the internal branch of the superior laryngeal nerve
and that internal branch of the superior laryngeal nerve is going to serve the the mucosa superior
to the vocal folds and we'll learn more about the vocal folds when we discuss the the larynx
this particular nerve is afferent and secretomotor to that mucosa superior to the vocal folds
the other branch which which we can see here is a little smaller on this specimen or more delicate
and it's coming down there it's running behind the bifurcation of the common carotid and it's picked
up there and continues on down where it innervates the cricothyroid muscle so that's the external
branch of the superior laryngeal nerve which is efferent or motor to the cricothyroid whenever
I have to quickly think about which is which you know I think about myself and you know I'd like
to think that I'm muscular on the outside or the external and sensitive or sensory on the inside or
the internal so let's let's follow the path of the the vagus as it continues to move down through the
carotid sheath it's going to send a branch to the pharyngeal plexus and we'll discuss that when we
talk about the pharynx but eventually the vagus is going to enter into the thorax as it passes
through the root of the neck and when it does so the vagus is going to send another branch to the
larynx called the internal I'm sorry called the recurrent laryngeal nerve that recurrent
laryngeal nerve is different on the right versus the left side so we'll we'll look at both now so
here is the right common carotid artery there is the right internal jugular vein and kind of
between them here we can see the the vagus nerve meandering down through and we know that we're in
the root of the neck because we see the right subclavian artery there we would see the right
subclavian vein continue there so between the two down comes the other vagus nerve and that vagus
nerve is transmitted through the thorax eventually it's going to end up in the abdominal cavity but
right past the root of the neck the right vagus nerve sends the right recurrent laryngeal nerve
looping around the right subclavian artery so that's really high in the root of the neck
that's going to continue on and it's going right for the trachea esophageal groove so there's a
groove between the trachea which is anterior and the esophagus which is posterior and it's right on
the side there and it travels up toward the lyrics on the left side here's the left common carotid
artery there's the left internal jugular vein and here's the left vagus nerve coming down as you can
see it shoots through the other root of the neck it's continuing on down Wow it's going really far
and then it sends the left recurrent laryngeal nerve wrapping around the concavity of the arch
of the aorta and that like its counterpart on the right is heading straight for the trachea
esophageal groove and then it finds that groove and ascends in that groove up to the larynx the
recurrent laryngeal nerves are sometimes referred to as the inferior laryngeal nerves whenever they
cross the plane of the cricoid cartilage which is approximately there so that cricoid cartilage as
will learn in the in the session of the lyrics is a ring of cartilage that forms the base of
the larynx and when these nerves pass that plane some sources will refer to the recurrent laryngeal
nerve as the inferior laryngeal nerve whatever you call it you know a rose is a rose is a rose
the recurrent or the inferior laryngeal nerve these are efferent to all of the other intrinsic
laryngeal muscles so all of the intrinsic laryngeal muscles with the exception of
cricothyroid are supplied by their innervation by the recurrent laryngeal and they're also afferent
and secrete a motor to the mucosa inferior or distal to the vocal folds the vagus nerves are
going to have a large role in the thorax they're going to supply the the parasympathetic input
to the the cardiac plexus the cardiac autonomic plexus the respiratory or pulmonary plexus ease
there they supply the esophageal plexus and then they're going to be parasympathetic to the the
gut tube and organs of the gastrointestinal system in the in the abdominal pelvic cavity as we'll see
let's take a look again back at the the neck and here we're going to see the accessory nerve
it will be highly variable I'm going to just kind of trace over it here the accessory nerve usually
has a slight sort of telephone cord like bent to it and now that I've I've outlined it there I'm
going to erase that so that that you can more clearly see it and I'll just circle that there
the accessory nerve or cranial nerve 11 is an interesting cranial nerve it's a predominantly
efferent or motor mainly motor nerve as we say it arises from the cervical spine as rootlets
and then those rootlets coalesce into the nerve and that nerve enters the skull via the foramen
magnum and then it travels up and leaves through the jugular foramen with the glossopharyngeal and
vagus nerves so cranial nerves nine ten and eleven all exit through the jugular foramen
and we can't see the the jugular foramen here on this particular skull but it would be deep
to this area here we can see a very distended IJ heading up in in that particular direction and so
the accessory nerve is efferent or motor to the sternocleidomastoid and trapezius muscles we say
mainly motor they may there may be some afferent fibers contained within the accessory nerves some
sources do discuss this but predominantly the afferent to SCM and trapezius muscles are branches
from the ventral primary rami of cervical nerves two three and four as we've discussed
the spinal nerves as they exit from the the spinal cord are going to exit as ventral and dorsal
primary Rami now in the so if I were to just draw a spinal nerve here so this would be the root of
that spinal nerve there's that the dorsal I'm sorry that would be the trunk of the spinal nerve
there's the dorsal roots and then that dorsal root ganglion and then those dorsal root let's there's
the ventral root and the ventral rootlets so afferent comes in through the dorsal efferent goes
out through the ventral and so this trunk here is mixed and then we have a dorsal primary ramus
and a ventral primary ramus so wherever you see vpr that's ventral rami or ramus it's typically
these ventral primary Rami which come together in certain areas to form plexuses a plexus is a
group of of rami that coalesce together and then form various nerves and the advantage here is
that different spinal nerve levels are able to contribute to different nerves so when we talk
about the cervical plexus we're talking about the ventral primary Rami of cervical nerves C 1 C 2 C
3 and C 4 one of the nerves that arises from the cervical plexus is the phrenic nerve and we can
see the phrenic nerve descending down here that would be this lovely and it enjoys a very special
relationship with the anterior scalene muscle which has been reflected away and that is that
the phrenic nerve runs just anterior and upon the anterior scalene muscle so then the phrenic nerve
is running between the subclavian artery and what would be the subclavian vein at the root of the
neck and it continues on down to innervate the diaphragm the phrenic nerve has its roots from
c3 4 and 5 so you'll notice that c5 sometimes will contribute to the cervical plexus but it's
more a component of the next plexus that will discuss the brachial plexus so that phrenic nerve
sometimes you'll hear the mnemonic c 3 4 5 keeps the diaphragm alive because that's what innervates
the diaphragm so moving more inferiorly now or distally down the the spinal cord we have
the brachial plexus the brachial plexus consists of ventral primary ram i from c5 through t1 and
while I'm not a dancer I always remember this as the brachial plexus is C 5 6 7 81 now these are
what are known as the roots of the brachial plexus the roots of any plexus are ventral primary ram I
students get confused all of the time because in the sense of the spinal cord if you recall
with dorsal and ventral roots these come together to form a trunk and then there's a dorsal ramus
and a Ventura ramus so these here are the roots of a spinal nerve these here are the RAM I of the
spinal nerve but in the context of a plexus it's these Ram I and in particular with the cervical
and brachial plexus it's the ventral primary ram i which are the roots of these plexuses so
don't get that confused the brachial plexus is going to innervate both efinitely and efferent
lee the upper limb inclusive of the shoulder so we can see very well here so this is c5 c6
c7 c8 and t1 these roots coalesce so c5 and c6 come together to form the superior trunk
see seven continues without coalescing to form
the middle trunk and then c8 and t1 coalesce to form the inferior trunk
these trunks are then going to form divisions these divisions will form chords and from roots
trunks divisions and chords we have branches the branches are the individual nerves that
come out of the brachial plexus and there's a mnemonic for everything in anatomy and that
mnemonic for the brachial plexus that you hear quite a bit is Randy Travis drinks cold beer
roots trunks divisions cords and branches so we've discussed two cranial nerves the
vagus cranial nerve 10 and the accessory cranial nerve 11 the cervical plexus and one of its motor
branches the phrenic the brachial plexus and its structure thank you for your time