The vagus nerve is a cranial nerve.
It is the longest of the cranial nerves.
It has the most extensive distribution. Vagus
is derived from a word meaning “wandering”
and so, it does wander throughout the entire
body almost. It conveys various fiber types.
These are somatic, afferent or sensory fibers.
Going to the body wall, we also will see visceral
afferents. So, these are sensory fibers that
are conveying senses from the organs. Somatic
afferents and so these are motor fibers to
We also have two types of visceral afferent
fibers being conveyed to the vagus nerve.
These will be general visceral afferents as
well as special visceral afferents. And if
we take a look at the course of the left vagus
nerve, we see the left vagus nerve descending
from the neck into the thoracic cavity and
it is crossing anterior to the arch of the
aorta. And the visceral afferents that are
conveyed in the vagus nerve, these afferents
are parasympathetic fibers.
Here, we are looking at the same image, but
I want to call your attention to the right
side of this illustration. Here we have the
right vagus descending from the neck. It was
cut and removed to show more clearly some
additional structures in this region, but
here’s your right subclavian artery. The
right vagus nerve will course anterior to
your right subclavian and then, we see the
distal cut end of the vagus and then, we will
see it continuing in the thoracic cavity along
the right lateral margin of the esophagus
and left one will also start to occupy here
initially a similar course
on the left margin of the esophagus.
Now, let’s take a brief moment to explore
the various fiber types and their distribution.
This slide shows us the general visceral efferents
and the general visceral afferents. The general
visceral efferent fibers are innervating the
smooth muscle that’s associated with respiratory
tree. We also have the mucous glands that
are associated with the respiratory tree.
Hence, they are innervated by these visceral
general efferents. The heart also receives
distribution through this fiber type and these
same fibers are conveyed and distributed to
the esophagus. Sensory fibers from the viscera, the thorax,
constitute the general visceral afferents of the vagus nerve.
Here, we are looking at the distribution of
the vagus nerve to the heart. These general
visceral efferents are parasympathetic fibers
and they are shown in purple in this illustration.
So, we have our right vagus here purple, we
have our left vagus and then, you can see
branches are coming off the vagus nerves and
are distributed to the atria and then, very
sparse distribution to the ventricles and
the primary distribution to the ventricles
would be the coronary vessels that supply
Functionally, the parasympathetic fibers being
conveyed in the vagus will decrease the heart rate.
They have minimal influence on myocardial
contractility or force of contraction because
of that sparse distribution to the ventricles,
but they do directly vasodilate the coronary
vessels and then, those coronary vessels will
subsequently start to, then, constrict because
of the decrease in heart rate.
This particular slide is demonstrating the
parasympathetic fibers that are being distributed
to the esophagus. These are the general visceral
efferents again. We see both vagus right and
then, left here and we see various branches
that contribute to the innervation of the
esophagus, more distally.
What will happen is the left vagus will come
more anterior whereas the right will turn
more posterior in relationship to the esophagus
and the left vagus will become what is known
as the anterior vagal trunk. The right vagus
being rotated posteriorly will become the
posterior vagal trunk and this is due to developmental
events of the primitive GI tube being rotated
to the right side of the body. There is a
pneumonic to help you remember which vagus
is the anterior trunk versus the posterior
trunk. That pneumonic is LARP and this simply
means that the left becomes anterior, the
right vagus will become a posterior.
The visceral efferents, that are generally
supplying the esophagus, are involved in peristalsis
of the esophagus and the parasympathetics
will also allow for a bolus of food to move
from the esophagus into the cardiac region
of the stomach, thereby relaxing the lower
esophageal sphincter. If there is damage to
the parasympathetic components anywhere along
this pathway within the wall of the esophagus
via parasympathetic components, mediastinal
mass compressing the vagus or even a stroke
where the motor nuclei are located, any one
of those kinds of events can cause failure
of the sphincter mechanism and as a result,
you have a disease or disorder called achalasia.
Within the thoracic cavity, the vagus nerve
will give rise to recurrent laryngeal nerves.
Both of these recurrent laryngeal nerves are
detected in this illustration. So, let’s
take a brief moment for you to take a look
at them. Here is your left vagus nerve coursing
anterior to the aortic arch. And right at
this particular point, we see the left recurrent
laryngeal nerve branching off the left vagus.
It will then wrap underneath the aortic arch
and then, will ascend posterior to it into
the neck and here, we can pick it up again
and it will disappear under cover of the thyroid
gland that we see here more superiorly.
On the right side, the right recurrent laryngeal
nerve has a slightly different course to ascend
into the neck and what it will do is, it will
issue from the right vagus, we see the right
vagus here, right vagus, as mentioned before,
will cross anterior to the subclavian. The
subclavian has been cut right along here distally
and it’s more proximal attachment will be
back in this general direction, but right
here, we can see coming up this distal segment
of the vagus, we can see the right recurrent
laryngeal nerve. It would then ascend along
the trachea and then, pass deep or posterior
to the right subclavian vein and then would
continue its ascend upwards into the neck
under cover of the thyroid.
The recurrent laryngeal nerves convey special
visceral efferents and these visceral special
efferents are going to innervate all the intrinsic
muscles of the larynx except for the cricothyroid.
The special visceral efferents will also innervate
muscles of the pharynx with the exception
of the thyropharyngeus muscle and the palate
with the exception of the tensor veli palatini.
If you have a mediastinal mass such as the
mediastinal tumor, that tumor could, in some
cases, encroach upon one of your recurrent
laryngeal nerves and let’s just say, the
mass is over here on the left side encroaching
upon the left recurrent laryngeal and if there
is too great of a involvement of that mass
on that recurrent laryngeal nerve, that can
lead to hoarseness and even vocal cord paralysis.