Vagus. Vagus is the 10th cranial nerve, comes out through
the jugular foramen, lies within the carotid
sheath. It’s so close to the midline, it
runs in front of the subclavian artery.
So far, so good. Now that distinguish the
difference between the right and the left
vagus. On the right vagus, as it passes in front
of the subclavian, the recurrent laryngeal
nerve is given out which hooks around the
subclavian and comes back. That’s your recurrent
On the left side, it goes down to the arch
of aorta, then it hooks back and then you
have ligamentum arteriosum.
To the left of ligamentum arteriosum
it hooks and comes back to the neck. So on
the right side it is hooking back on the subclavian
artery, on the left side it’s hooking back
on the arch of aorta. So the action of the vagus
and the glossopharyngeal are quite similar
in the pharynx and the larynx and superiorly.
What are the main branches of the vagus? Just
tell me some main branches you can think of.
Recurrent laryngeal you said, that’s fine.
Is it the external laryngeal?
Is that a branch of the vagus?
That’s right. Though you have,
you are right, because you said that. Vagus
gives off a superior laryngeal nerve which
divides into an external laryngeal and an internal
laryngeal, and then you have the recurrent
laryngeal coming down. So because, this essentially
supplies the whole of larynx. So your superior
laryngeal nerve divides into external laryngeal
and internal laryngeal. The external laryngeal
nerve supplies the cricothyroid. All
the other motor muscles in the larynx are
supplied by the recurrent laryngeal.
The action of cricothyroid is for high pitched
voice. So if a patient has got a superior
laryngeal nerve injury or an external laryngeal
nerve injury, they will have absence of high
pitched voice. But if the recurrent laryngeal
nerve is affected, what happens?
Lost voice. One side stutters.
What if one side is divided, what is it? Hoarseness.
Bilateral? Stridor or aphonia. Completely,
there’s probably no speech at all.
Sensation, above the vocal cords is supplied
by the internal laryngeal nerve, below the
vocal cord is supplied by the recurrent laryngeal.
So similar to your tongue, if you divide
it into --
Does it abduct the vocal cords as well?
Abduction of the vocal cords as well.
Was that the recurrent laryngeal or was that
the superior laryngeal one?
Ah, recurrent laryngeal because superior laryngeal
supplies only the cricothyroid, yeah. So if
you divide your larynx into above the vocal
cord and below the vocal cord, below the vocal
cord, both sensory and motor is by recurrent
laryngeal. Above the vocal cord, the cricothyroid
is supplied by the external laryngeal and
the sensation is supplied by internal laryngeal.
Both are coming off the superior laryngeal.
You’re right. Now, then you have the
I’m sorry but do you mind slowing down?
Don’t get confused with this, just remember
all the muscles in the larynx are supplied
by the recurrent laryngeal, except cricothyroid
which is supplied by the external division
of the superior laryngeal.
Okay, that’s it.
Now, take your sensation below the vocal cord,
it’s by the recurrent laryngeal and above
the vocal cord it is by the internal division
of the superior laryngeal. So that’s
it, that’s all they will ask about the larynx.
That’s it. Then they might ask you something
on the pharynx. What is the pharynx supplied
by, mainly? What are the main muscles in your
Constrictors. So you have your superior constrictor,
middle constrictor, inferior constrictor.
You’re right. Yeah palatoglossal, styloglossus,
stylopharyngeus, those muscles. They are
all supplied by the vagus, except the stylopharyngeus.
In other words, your larynx, pharynx has to
be from vagus with a bit of exception. The
glossopharyngeal nerve doesn’t have too
many motor branches. It has got the lesser
petrosal nerve and a couple of small branches
but nothing major. Vagus is a big one. Vagus
is the one that mainly supplies most the neck.
The other way you can remember is you know
you have a nasopharynx,
oropharynx, and hypopharynx.
So, nasopharynx, oropharynx, and hypopharynx.
We won’t go into detailed anatomy because
that is more part like B, but here what you
need to remember is your hypopharynx, remember
cranial nerve X because it’s lower. Oropharynx
is IX and this is V. That means the maxillary
division of trigeminal nerve supplies the nasopharynx.
So that’s quite easy to remember. If at
all you’re asked about nerve supply of the
oropharynx, hypopharynx or the nasopharynx.
So the first one is nasopharynx, oropharynx,
hypopharynx and remember V, IX, and X.
I think I’ll just go through
some of the slides now. I know that similar
to your upper limb everything is available
on the slides so --
In the MCQs they will specifically asked about
the triangles of --
Boundaries of the kind of individual triangles
that are in the neck or do we just need to
grossly be aware of them and not the actual --
You need to be aware of the submandibular triangle
and the carotid triangles because they are
the most important ones. You don’t have
to know about the posterior triangle divisions,
but these ones you need to know, because they
are anatomically and clinically quite significant.
So as I said, there’s no new information
in these slides, so don’t worry about going
through detail. Just to reinforce what
We discussed about the hyoid, thyroid cartilage,
cricothyroid membrane and then you have the
cricoid cartilage. Significance, the larynx
and the trachea, does the junction at the
cricoid cartilage, and the pharynx with the
esophagus. So pharynx begins
as the esophagus from C6 vertebra and the trachea
is formed from C6 level as well. Right,
this is what we went through, so that’s your
carotid triangle and occipital triangle.
Submental triangle, submandibular triangle,
carotid triangle, occipital triangle, supraclavicular
triangle or the subclavian triangle.
Theory, you don’t have to read it now. It
will be available online. I’m sure you don’t
have to know it in detail as long as you have
a fair idea of the main muscles, or the only
two muscles you need to remember. Well if
they say four that will be sternocleidomastoid,
trapezius, big triangles, then your
digastric and omohyoid. That’s it.
Triangles and structures in each triangle. Of this,
submandibular triangle is very important,
remember that, and the carotid triangle, even
though there are lots of structures, all you
need to remember is carotid sheath. If you
remember that, you know that jugular vein,
carotid artery, vagus. So if you remember
these three, everything else is fine, because
these are the three big ones.
Posterior triangle. All you need to remember
is spinal accessory nerve, branches of the
cervical plexus. There are these cutaneous
ones, brachial plexus and phrenic, but phrenic
is quite away from the clavicle here. Carotid
artery we don’t have to discuss, the only
thing is the bifurcation occurs at the level
of C4 and then the branch is the external
carotid, exactly what we discussed before.
Right, the only one thing that I need to point
out here, it’s not very anatomical, but
carotid artery stenosis, more than 70% is
significant. You need to know the clinical
indications. You need to know this amaurosis fugax,
at what point you offer surgery to a patient
with carotid artery stenosis. So the current
guideline say anything between 70 - 99% of stenosis,
you need to offer surgery, but 100% stenosis
you don’t have to treat. So this is quite
important. You may be getting a question in
the exam, so if you have a patient with carotid
artery stenosis, if it’s 50% of plaque,
wait and observe. If it becomes 70% then you
get worried. That’s when it’s throwing
off embolus. So between 70 and 99 you need
to operate, but if it is completely occluded,
what do you do?
It’s probably throwing off emboli.
That’s right. But the only thing you need
to do is you need to scan the other side.
Just to make sure that the other side is patent.
So if 70 - 99% is asymptomatic, do you still treat?
If they are absolutely asymptomatic then perhaps
not, but be very careful because they can
just have a stroke anytime. They don’t have
to have a TIA, they can just have a stroke.
So it is better to treat.
Basically, it’s coming anyway because they
have had a symptom or something apparently --
That’s right, yeah but the guideline is
70 - 99%, so in the exam if they ask you say yes.
Parotid region, branches of the facial nerve, you
know that. Parotid gland, parotid ducts and
those are your branches. And that is exactly what
Is it also called Stensen’s duct? The parotid
duct, is it also called Stensen’s duct?
Stensen’s duct. The submandibular duct is
called the Wharton’s duct. Stensen’s duct
is 5 cm long. It comes from the anterior border
of the submandibular gland, overlies the masseter
muscle, pierces the buccinator and empties
into the upper second molar tooth. So if you
clench your teeth and roll your finger, you’ll
feel the parotid duct. On the finger is the
parotid duct and that’s the one which pierces
the buccinator. Okay, so that’s fine.
Branches of the parotid,
you know that. We touched upon this when
we discussed submandibular gland. So the question
might be related to excision of the submandibular
gland, lesion or gland. What are the nerves
that can be injured? So V1, V2, V3, this is
what we said,
ophthalmic, maxillary and mandibular. Okay,
as per here, the commonest reason for epistaxis
Do you mean cause of --
Cause of epistaxis. Usually in the epistaxis,
the 90% of it occurs in the Little’s area
or the Kiesselbach's plexus. Your question
will be related to the arteries in that area.
Sphenopalatine, yeah. Greater palatine, yeah,
very good. Labial, superior labial.
Septal arteries, yeah, and mainly the ethmoidal.
Anterior and posterior ethmoidal arteries.
What is the other significance of the
Little’s area apart from --
Infection! Go on, tell me…
It kind of causes cavernous sinus thrombosis
because of the relation to the cavernous sinus
to get infection.
How is the cavernous sinus related to that area?
You’re right but -- Is it because of the
arterial supply that
leads directly to the cavernous sinus?
Yes, because whenever you have an arterial
supply, the venous drainage will also be going
back to that area. In this area, or the
Little’s area of the nose, is where your
external carotid anastomosis with the internal
carotid. Essentially the veins are
going back into the cavernous sinus. So you
get an infection in this area that leads to
cavernous sinus thrombosis, that’s because
of this anatomy. So there are not many
small arteries you need to know in the face,
but these ones are asked, these names.
The specific branches of external carotid
and internal carotid because of Little’s
area, because of epistaxis.
Right, just one slide for larynx, that’s
all you need to know. That’s it. Exactly
what we discussed. I’ll leave it to you
to remember it. Motor and sensory innervation
of the larynx is mainly through two branches
of the vagus, superior and recurrent. Superior
divides into external, internal.
External supplies cricothyroid muscle, and recurrent
supplies all the muscles in the larynx except
Sensory above the vocal cord is internal
laryngeal and below is recurrent. Another
question that comes up: Recurrent laryngeal
nerve injury, unilateral injury you get hoarse
voice, bilateral injury, partial airway obstruction
or aphonia. External laryngeal nerve injury,
patient’s inability to produce high pitched
sounds. So this question will be related to
nerve injury or thyroidectomy. Post-thyroidectomy
complication will be a question on this. Post-thyroidectomy,
patient iss unable to produce high pitched
sound and the patient has
got hoarse voice, which nerve is injured?
And the question would be, unilateral recurrent
laryngeal nerve, bilateral recurrent laryngeal,
external laryngeal, internal laryngeal. Okay?
Pharynx. Nasopharynx. Oropharynx. Laryngopharynx
or the hypopharynx. So this what I said: V,
IX, X. So remember I said about all your constrictor
muscles? Middle constrictor, superior constrictor,
inferior constrictor, they are all in that
laryngopharynx, right? The laryngopharynx.
So that’s why they are all by the vagus.
Thyroid. The malignancy of thyroid is important,
but as far as anatomy is concerned all you
need to know is the blood supply of the thyroid.
So we discussed about the superior thyroid
artery which comes from the external carotid.
Then you have the inferior thyroid coming
from the thyrocervial trunk, which we’ll
cover when we do the thorax, and then you
have the thyroid ima artery. So these are
the main arteries supplying the thyroid gland.
So superior thyroid, inferior thyroid,
and thyroid ima artery. Thyroidectomy. The
only reason for this slide is just to reinforce
the idea that you get exactly the same injury
in the thyroidectomy and the nerve injuries
related to recurrent laryngeal.
Lymph nodes of the neck. This is what
I said, Level I, IA, IB. Level II. Level
III. Level IV. The C1, C2 describes the name
of lymph nodes. So Level I, level II, level III,
level IV, evel V. And the next slide
goes through the anatomy of the lymph nodes
and what are the areas drained. So this is
something you may have to revise quickly before
your exam because they might give you a clinical
scenario and say, “Which lymph node does it drain to?”