206 Neuroanatomy: Draw It to Know It
Oculomotor Nuclei ( Advanced )
Here, we will draw the Warwick model of the oculomo-
tor complex and the perioculomotor cell group model.
Let’s begin with the oculomotor complex. In the 1950s,
R. Warwick created a classic model for the oculomotor
complex, and although details of this model have been
updated over time, its basic construct remains unchanged.
Th e model shows that the superior rectus subnuclei proj-
ect contralaterally, the single levator palpebrae subnu-
cleus projects bilaterally, and the remaining subnuclei
project ipsilaterally. As an important clinical corollary,
levator palpebrae subnucleus lesions naturally cause
bilateral eye muscle palsies and superior rectus subnu-
cleus lesions also produce bilateral palsies because when
the superior rectus fi bers exit their subnucleus, they
immediately pass through the contralateral subnucleus.
Now, let’s draw Warwick’s model of the oculomotor
complex in sagittal view. Label the rostral–caudal and
dorsal–ventral planes of orientation. First, let’s draw the
lateral subnuclei from ventral to dorsal. Draw the long ,
narrow ventral subnucleus; designate it as innervating
the medial rectus (although in actuality, three separate
oculomotor regions supply the medial rectus muscle).
Above the ventral subnucleus, draw the intermediate sub-
nucleus, which innervates the inferior oblique; and above
it, draw the dorsal subnucleus, which innervates the infe-
rior rectus. Medial to these subnuclei, draw the medial
subnucleus, which innervates the contralateral superior
rectus (note: this subnucleus is commonly unnamed).
Th en, on the dorsocaudal surface, draw the small central
caudal subnucleus, which innervates the bilateral levator
palpebrae. On the rostral surface, draw the visceral nuclei,
which include the Edinger–Westphal nucleus, anterome-
dian nucleus, and the nucleus of Perlia.^10
Next, let’s draw the perioculomotor cell group, which
places the Edinger–Westphal nucleus, anteromedian
nucleus, and nucleus of Perlia into a larger context of
neural substrate responsible for the accommodation
refl ex. Th e accommodation refl ex (or near-response) is a
three-part refl ex that brings near objects into focus
through lens thickening, pupillary constriction, and
inward rotation of the eyes — eye convergence. First,
indicate that our diagram is in coronal view. Th en, draw
a large, long nucleus to represent a consolidation of
the oculomotor complex; note that this representation
excludes the visceral nuclei, which will be drawn as
part of the perioculomotor cell group. Next, along
the dorsal aspect of the oculomotor nucleus, draw the
preganglionic perioculomotor cell group; show that
the Edinger–Westphal nucleus lies within this part of
the perioculomotor cell group. Th e preganglionic cell
group is responsible for producing the lens thickening
and pupillary constriction responses of the accommoda-
tion refl ex. Next, along the rostral–caudal length of the
medial aspect of the oculomotor nucleus, draw the
motoneuron division of the perioculomotor cell group;
it innervates the multiply innervated muscle fi bers of the
accommodation refl ex, which produce the eye conver-
gence response. Show that the motoneuron division of
the perioculomotor cell group encompasses the antero-
median nucleus, anteriorly, and the nucleus of Perlia in
mid-anteroposterior position. Note that due to the actual
complexity of this nuclear complex, we should not
attempt to draw discrete functional meaning from the
positions of the Edinger–Westphal nucleus, anterome-
dian nucleus, and nucleus of Perlia from this diagram —
these nuclei are included, here, only to provide historical/
anatomic context to our perioculomotor cell group
model, and we should still simply consider them to
broadly enact the visceral actions of the oculomotor
nerve.
Finally, in regards to the accommodation refl ex, itself,
consider that supranuclear control of the perioculomo-
tor cell group comes from widely distributed areas,
which include the supraoculomotor area (which lies
within the mesencephalic reticular formation just dorsal
to the oculomotor complex) and numerous cerebral
and cerebellar smooth pursuit centers described in
Chapter 23.^2 , 6 – 9 , 11 , 12