182 Neuroanatomy: Draw It to Know It
Cranial Nerve Nuclei
Here, we will draw the organization of the cranial nerve
nuclei in coronal view. Draw a coronal section through
the brainstem and upper cervical spinal cord and mark
the boundaries of the midbrain, pons, and medulla.
Th en, denote the sulcus limitans, which divides the
brainstem into basal and alar plates. Along the top of
the brainstem, list the positions of the cell columns. At
the medial end of the basal plate (ie, at the midline of the
brainstem), label the general somatic eff erent column;
lateral to it, label the general visceral eff erent column;
continuing laterally, label the special visceral eff erent
column; then, label the combined general visceral aff er-
ent and special visceral aff erent columns; then, label the
special somatic aff erent column; and fi nally, label the
general somatic aff erent column.
We organize the cranial nerves into three groups of
nerves: the somatomotor (aka somitic), solely special
sensory, and pharyngeal arch derivatives. Each of the dif-
ferent cranial nerve sets involves various populations of
cell columns. Th e somatomotor set is nearly exclusively
general somatic eff erent, but also includes a single gen-
eral visceral eff erent nucleus; the solely special sensory
set is exclusively special somatic aff erent; and the pha-
ryngeal arch derivatives contain all of the cell column
types except for the general somatic eff erent and special
somatic aff erent cells.
Begin with the somatomotor set. It lies in midline
and comprises cranial nerves 3, 4, 6, 12, and 11. Th e
somatomotor set is considered the brainstem extension
of the spinal neurons because it innervates somite tissue
derivatives. However, whereas the spinal neurons con-
tain general somatic eff erent and aff erent and general
visceral eff erent and aff erent cells, the somatomotor cra-
nial nerve set comprises only general somatic eff erent
cells and a single general visceral eff erent nucleus — the
Edinger–Westphal nucleus. To demonstrate the actions
of the somatomotor cranial nerve set, move your eyes in
all directions using cranial nerves 3, 4, and 6; protrude
your tongue using cranial nerve 12; and shrug your
shoulders using cranial nerve 11. Notice that these move-
ments involve midline muscles, which helps us remem-
ber that the general somatic eff erent cell column lies near
to midline.
Now, in the general somatic eff erent column, in
descending order, draw the nuclei of the somatomotor
set. Label the oculomotor nucleus of cranial nerve 3 (the
oculomotor nerve): it extends from the upper to the
lower midbrain, spanning the height of the superior col-
liculus and reaching the level of the inferior colliculus.
Th en, underneath the oculomotor nucleus, label the tro-
chlear nucleus of cranial nerve 4 (the trochlear nerve): it
is a small nucleus that lies in the caudal midbrain at the
level of the inferior colliculus. Next, label the abducens
nucleus of cranial nerve 6 (the abducens nerve): it spans
from the mid to the lower pons. Now, show the hypo-
glossal nucleus of cranial nerve 12 (the hypoglossal
nerve), which spans most of the height of the medulla.
Th en, label the accessory nucleus of cranial nerve 11 (the
accessory nerve) in the upper cervical spinal cord: it
spans the fi rst fi ve cervical spinal cord levels.
Next, in the general visceral eff erent cell column, draw
the Edinger–Westphal nucleus of cranial nerve 3 (the
oculomotor nerve), which lies in the rostral midbrain.
Note that although we distinguish this nucleus from the
oculomotor nucleus, it is actually a rostral subnucleus of
the oculomotor complex, which comprises all of the
nuclei of cranial nerve 3.
Now, we will draw the solely special sensory set, which
comprises cranial nerves 1, 2, and 8, all of which are
purely sensory. Cranial nerve 1 is involved in olfaction,
cranial nerve 2 in vision, and cranial nerve 8 in vestibular
and auditory function. Only cranial nerve 8 resides
within the brainstem. Cranial nerve 1 comprises tiny
nerve fi laments that traverse the cribriform plate, and
cranial nerve 2 is the set of optic nerves that run under-
neath the base of the brain.