154 Neuroanatomy: Draw It to Know It
The Pons
Here, we will draw an anatomic, axial cross-section of
the pons. First, 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, in the
opposite corner, draw a small axial pons section and sep-
arate the large basis from the comparatively small teg-
mentum. For our main diagram, exclude the bulk of the
basis to make room for the complexity of the tegmen-
tum. Next, label the left side of the page as nuclei and the
right side as tracts.
First, in the basis, draw the corticofugal tracts, which
we pare down to the corticospinal and corticonuclear
tracts because the corticopontine fi bers synapse within
the pons, itself. Draw the pontine nuclei within the pon-
tine basis; the frontopontine and additional corticopon-
tine fi bers synapse within these nuclei. Next, show that
the pontine nuclei send pontocerebellar tracts into the
cerebellum via the middle cerebellar peduncle (aka
brachium pontis) as part of the corticopontocerebellar
pathway.
Now, draw the inferior cerebellar peduncle, which
comprises the restiform and juxtarestiform bodies.
Spinocerebellar, reticulocerebellar, and olivocerebellar
fi bers pass through the restiform body, whereas the jux-
tarestiform body is primarily reserved for fi bers that pass
between the vestibular nucleus and vestibulocerebel-
lum.^8 Next, show that the superior cerebellar peduncle
(aka brachium conjunctivum) lies posterior to the infe-
rior cerebellar peduncle. Th e middle and inferior cere-
bellar peduncles are the main infl ow pathways into the
cerebellum and the superior cerebellar peduncle is the
main outfl ow pathway. Th e superior cerebellar peduncle
attaches to the upper pons and midbrain; the middle
cerebellar peduncle attaches to the pons and extends to
the pontomedullary junction; and the inferior cerebellar
peduncle attaches to the lower pons and medulla. Now,
draw the anterior spinocerebellar fi bers in the postero-
lateral pons; the other spinocerebellar pathways enter
the cerebellum below the pons through the inferior cer-
ebellar peduncle (see Drawing 7-5).
Next, show that in the pons, the medial lemniscus lies
medially — unlike in the midbrain, where the red nuclei
push the medial lemniscus out laterally. Th en, lateral to
the medial lemniscus, draw the anterolateral system, and
along the posterior wall of the medial lemniscus, draw
the anterior trigeminothalamic tract.
Now, let’s show the supplementary motor and sensory
tracts of the pontine tegmentum. Indicate that the
medial longitudinal fasciculus and the tectospinal tract
continue to descend through the dorsal midline tegmen-
tum and that the central tegmental tract descends
through the dorsal, central tegmentum. Also, include
the rubrospinal tract just posterior to the anterolateral
system. Now, label the cerebrospinal fl uid space of the
pons as the fourth ventricle and show that the central
gray area surrounds it. Next, label the locus coeruleus in
the posterior tegmentum, just in front of the central gray
area.
Although technically the locus coeruleus spans from
the caudal end of the periaqueductal gray area in the
lower midbrain to the facial nucleus in the mid-pons,
locus coeruleus nuclei are most heavily concentrated in
the pons. Th e locus coeruleus nuclei are nearly entirely
noradrenergic and, thus, are far more uniform in their
neurotransmitter makeup than the periaqueductal gray
area and even more uniform than the raphe nuclei, which
are mostly serotinergic.
Next, label the reticular formation and raphe nuclei
and then label the nuclei of cranial nerves 5, 6, 7, and
8 in the dorsal pontine tegmentum. Cranial nerves 6 and
7 lie within the mid to low pons; cranial nerve 8 lies
within both the pons and medulla; and portions of cra-
nial nerve 5 lie along the height of the brainstem. Again,
note that our diagram does not refl ect the medial-lateral
position of the cranial nerve nuclei. Next, draw the
pontine components of the auditory system: the lateral
lemniscus in the lateral tegmentum and the trapezoid
body and superior olivary nucleus in the anterolateral
tegmentum.^1 – 11