148 Neuroanatomy: Draw It to Know It
Brainstem Composite — Axial View
Here, we will draw an axial composite of the brainstem:
a consolidation of the diff erent brainstem levels into a
single general organizational pattern. First, draw an
ovoid outline of the brainstem. Th en, show the axes of
our diagram: indicate that the anterior pole is at the
bottom of the page and that the posterior pole is at the
top and then show the anatomic left –right orientational
plane. Next, label the left side of the page as nuclei and
the right side of the page as tracts.
Now, divide the brainstem from anterior to posterior
into its basis, tegmentum, and tectum. Th e basis com-
prises descending white matter tracts and certain supple-
mentary motor nuclei. Th e tegmentum is the central
bulk of the brainstem; it contains the cranial nerve
nuclei, neurobehavioral cells, ascending sensory tracts,
additional supplementary motor nuclei, and the supple-
mentary motor and sensory tracts. Th e tectum is the
roof of the brainstem. In the midbrain, the tectum is
the quadrigeminal plate, whereas in the pons and
medulla, by at least one commonly held defi nition, the
tectum is limited to the nonfunctioning medullary
velum. Note, however, that select authors include the
superior cerebellar peduncles as part of the pontine
tectum, as well.1–3
Within the basis, show the ventral-lying corticofugal
tracts, which comprise the eff erent fi ber tracts from the
cerebral cortex; they include the corticopontine, corti-
conuclear (aka corticobulbar), and corticospinal tracts.
Th e corticonuclear tracts peel off and synapse in target
nuclei as they descend the brainstem; the corticopontine
tracts synapse in the pontine basis; and the corticospinal
tracts pass through the medullary pyramids to reach
their targets in the spinal cord.
Moving posteriorly, label the supplementary motor
nuclei, which in the midbrain include the substantia
nigra and red nucleus; in the pons, the pontine nuclei;
and in the medulla, the inferior olive. Next, in the ante-
rior tegmentum, label the medial lemniscus pathway —
the major large fi ber sensory pathway from the body.
Th en, lateral to it, label the anterolateral system pathway,
which, most notably, carries the spinothalamic tract —
the major small fi ber sensory pathway from the body.
Next, posterior to the anterolateral system, label the
trigeminothalamic tracts, which carry sensory informa-
tion from the face.
Now, in the posterior tegmentum, label the cranial
nerve nuclei. Th e cell bodies for cranial nerves 3–10 and
cranial nerve 12 lie within the brainstem (cranial nerve
11 lies in the upper cervical spinal cord). Next, label the
neurobehavioral cells, which include the periaqueductal
gray area in the midbrain; the locus coeruleus in the
pons; and the raphe nuclei, which span much of the
height of the midline brainstem. Th en, label the broad
reticular formation in the tegmentum.
Now, label the supplementary motor and sensory
tracts, which include the medial longitudinal fasciculus
and tectospinal tracts, which run the midline height of
the brainstem, and the central tegmental and rubrospinal
tracts. Next, label the brainstem auditory components,
which are the cochlear nucleus, superior olivary nucleus,
trapezoid body, inferior colliculus, and lateral lemniscus.
We address these components in detail in Drawing 14-4.
Now, label the cerebrospinal fl uid space, which in the
midbrain is the cerebral aqueduct and in the pons and
medulla is the fourth ventricle. Lastly, label the cerebellar
peduncles: superior, middle, and inferior.^1 – 11