180 Neuroanatomy: Draw It to Know It
Spinal & Cranial Nuclear Classifi cation
Here, we will draw the spinal neurons and the brainstem
cranial nerve nuclei in axial view. Draw an axial cross-
section through the spinal cord. First, divide the spinal
cord gray matter into alar (sensory) and basal (motor)
plates. Th en, divide the gray matter into three anatomic
horns: posterior, intermediate, and anterior. Now, label
the cell columns: general somatic aff erent in the poste-
rior horn, general somatic eff erent in the anterior horn,
general visceral aff erent in the posterior intermediate
horn, and general visceral eff erent in the anterior inter-
mediate horn.
Next, let’s draw the cranial nerve nuclear cell columns.
Th ey share the same general layout as the spinal neurons
but have two key anatomic diff erences. One diff erence is
that in the brainstem, the posterior-lying alar plate shift s
laterally to make room for the fourth ventricle; there-
fore, all of the cranial nerve nuclei end up oriented along
the horizontal axis of the dorsal brainstem tegmentum.
To understand this shift , imagine opening an orange —
the dorsum of the orange swings out laterally. A second
diff erence between the brainstem cell columns and the
spinal cord is that the brainstem involves additional cell
columns — the special visceral eff erent and aff erent cell
columns and the special somatic aff erent cell column.
Th e special visceral cell columns are part of the pharyn-
geal arch (aka branchial arch) cranial nerve derivatives,
which appear early in embryogenesis as bar-like ridges
that contain the ectoderm, endoderm, and mesoderm
that form the skeletal tissue, musculature, and linings of
the head and neck. Th e pharyngeal arches produce cra-
nial nerve, arterial, and musculoskeletal derivatives.^5
Now, let’s draw the cranial nuclear columns of the
brainstem. Draw one side of an axial brainstem compos-
ite: a compression of all three brainstem levels. Divide it
from posterior to anterior into tectum, tegmentum, and
basis. Th e cranial nuclear cell columns lie within the
dorsal tegmentum, just in front of the cerebrospinal fl uid
space. Next, label the sulcus limitans in the fourth ventri-
cle; it separates the eff erent from the aff erent cell columns.
Now, begin with the cranial homologues of the spinal
nerves: in the basal plate, from medial to lateral, draw the
general somatic eff erent and general visceral eff erent cell
columns, and in the alar plate, from medial to lateral,
draw the general visceral aff erent and general somatic
aff erent cell columns. Next, include the special somatic
aff erent column; within the upper medulla, its constella-
tion of subnuclei spans the width of the alar plate. Now,
we need to address the special visceral cell columns, both
of which hug the sulcus limitans. Draw the special visceral
eff erent cell column in the space between the general vis-
ceral eff erent cell column and the sulcus limitans. Th en,
join the special visceral aff erent cell column with the gen-
eral visceral aff erent column in the medial alar plate.
Note that some texts substitute the word “somatic”
with the word "sensory" when referring to the general
somatic aff erent and special somatic aff erent columns
and refer to them, instead, as the general sensory and
special sensory aff erent columns.^6 , 7