226 Neuroanatomy: Draw It to Know It
Cranial Nerves 9 & 10
Here, we will draw the glossopharyngeal nerve (cranial
nerve 9) and the vagus nerve (cranial nerve 10), together.
First, draw a sagittal view of the brainstem. Begin with
the inferior salivatory nucleus, which is a small nucleus
in the upper medulla. Indicate that it innervates the otic
ganglion with GVE fi bers of the glossopharyngeal nerve.
Th e otic ganglion provides parasympathetic innervation
to the parotid gland. Next, directly underneath the infe-
rior salivatory nucleus, draw the dorsal motor nucleus of
the vagus, which spans the remainder of the medulla.
Indicate that it provides parasympathetic innervation to
smooth muscle of the oropharynx and parasympathetic
innervation to viscera within the thoracoabdomen
through GVE fi bers of the vagus nerve. Its actions
include pulmonary bronchiole constriction, heart rate
reduction, and augmentation of gut peristalsis. Now,
draw nucleus ambiguus, which spans the height of the
medulla. Indicate that it innervates the throat muscles
with SVE fi bers of the glossopharyngeal and vagus
nerves. Its glossopharyngeal innervation is to stylopha-
ryngeus, which elevates the pharynx during speech and
swallowing, and its vagal innervation is to the pharynx,
larynx, select palatine muscles, and one tongue muscle:
palatoglossus. Next, show that nucleus ambiguus also
provides parasympathetic GVE innervation to the
carotid body and carotid sinus through the glossopha-
ryngeal nerve, and to the heart and aortic bodies through
the vagus nerve.
Now, draw the spinal trigeminal nucleus, pars cauda-
lis, which spans from the inferior medulla to the upper
cervical spinal cord. Indicate that inferiorly it receives
cutaneous sensory reception from GSA fi bers of the
glossopharyngeal and vagus nerves (and the facial nerve).
Its sensory aff erents originate from many sites of the
head and neck, including the oropharynx, external ear,
and the tympanic membrane; also, the GSA component
of the vagus nerve carries posterior cranial fossa dura
mater sensory input.
Finally, draw the solitary tract nucleus, which spans
the height of the medulla. Show that within its upper
(gustatory) region, it receives taste aff erents from the
posterior third of the tongue via SVA fi bers of the
glossopharyngeal nerve and from the epiglottis via SVA
fi bers of the vagus nerve. Th en, indicate that within its
lower (cardiorespiratory) region, it receives GVA fi bers
of the glossopharyngeal nerve from the carotid body
chemoreceptors and the carotid sinus (aka carotid bulb)
baroreceptors. Lastly, indicate that the solitary tract
nucleus receives GVA fi bers of the vagus nerve from the
thoracoabdomen: specifi cally, from the heart, barore-
ceptors in the aortic arch, chemoreceptors in the aortic
bodies, pharynx, larynx, lungs, and proximal gut.^13
Next, note that both the glossopharyngeal and vagus
nerves each have superior and inferior sensory ganglia
that are protected by the skull base; they lie within or
near to the jugular foramen. Cell bodies of the GSA
fi bers lie in the superior ganglia and those of the GVA
and SVA fi bers lie in the inferior ganglia.^10
Now, draw an axial view of the medulla. Show that
the glossopharyngeal and vagus fi bers exit the medulla
laterally through the post-olivary sulcus to enter the
cerebellomedullary cistern (aka inferior cerebellopon-
tine cistern). Th en, return to our sagittal diagram and
show that these nerve fi bers traverse the skull base
through the jugular foramen along with the accessory
nerve (cranial nerve 11) and the internal jugular vein.
Next, show that within the periphery, within the carotid
space, cranial nerves 9, 10, and 11 and also cranial nerve
12 (the hypoglossal nerve) and the internal jugular vein
and internal carotid artery run together.^1 – 8 , 10 – 12