260 Neuroanatomy: Draw It to Know It
Nuclei & Circuitry ( Advanced )
Here, we will draw the cerebellar nuclei and circuitry.
Label the left side of the page as the cerebellar nuclei.
Begin this diagram with a saddle-shaped cerebellar hemi-
sphere. Include along the surface a single fold, called a
folium. Th e folding of the cerebellum into lobes, lobules,
and folia allows it to assume a tightly packed, inconspic-
uous appearance in the posterior fossa. Th e cerebellum
has a vast surface area, however, and when stretched, it
has a rostrocaudal expanse of roughly 120 centimeters,
which allows it to hold an estimated one hundred billion
granule cells — more cells than exist within the entire
cerebral cortex. Note that this is in part due to the small
size of the granule cells, themselves. It is presumed that
the cerebellum’s extraordinary cell count plays an impor-
tant role in the remarkable rehabilitation commonly
observed in cerebellar stroke.^8 , 9 , 18
Now, indicate that the two main classes of cerebellar
nuclei are the cerebellar cortical neurons and the deep
cerebellar nuclei. Draw a magnifi ed view of the folium in
order to show the diff erent cerebellar cortical cell layers.
Indicate that on the outside is the molecular layer, under-
neath it is the interposed Purkinje layer, and on the inside
is the granule layer with the subcortical white matter
underneath it. Show that the molecular layer primarily
comprises cell processes but also contains stellate and
basket cells; the Purkinje layer contains a single layer of
large Purkinje cell bodies; and the granule layer is highly
cellular: it contains granule cells, Golgi cells, and unipo-
lar brush cells.
Next, let’s address the centrally located deep cerebel-
lar nuclei. At the bottom of the page, list their names.
From medial to lateral, they are the fastigial, globose,
emboliform, and dentate nuclei. Show that together
the globose and emboliform nuclei are also known as
the interposed nuclei. An acronym for the lateral to
medial organization of the deep nuclei is “Don’t Eat
Greasy Food,” for dentate, emboliform, globose, and
fastigial.
Th e deep cerebellar nuclei parse into specifi c func-
tional modules. Th e fastigial nucleus plays a role in both
the vestibulocerebellum and spinocerebellum; the inter-
posed nuclei are part of the spinocerebellum; and the
dentate nucleus is part of the pontocerebellum.
Now, let’s show the fl ow of information through the
cerebellum. Label the right-hand side of the page as cer-
ebellar circuitry. First, indicate that there are three main
types of cerebellar aff erent fi bers: climbing fi bers, mossy
fi bers, and multilayered fi bers, which are also known as
monoaminergic fi bers.
Show that climbing fi bers are excitatory fi bers that
originate solely from the inferior olive and pass via the
contralateral inferior cerebellar peduncle to the cerebel-
lum. Debate exists as to whether climbing fi bers use the
excitatory neurotransmitter aspartate or glutamate, but it
seems most probable that they use glutamate. Th ese olivo-
cerebellar fi bers are distinct in that each Purkinje cell is
innervated by a single olivocerebellar climbing fi ber. Note
that this pathway represents the inferior arm of the tri-
angle of Guillain-Mollaret, discussed in Chapter 9.
Now, show that the mossy fi bers are excitatory fi bers
derived from diff use cell populations within the brain-
stem and spinal cord. Th ey, like the climbing fi bers,
mostly use the excitatory neurotransmitter glutamate.
Lastly, show that the multilayered fi bers are derived
from neurobehavioral centers in the brainstem and dien-
cephalon, such as the locus coeruleus, raphe nucleus, and
the tuberomammillary nucleus of the hypothalamus.
Whereas the climbing and mossy fi bers are unquestion-
ably excitatory, the role of the multilayered fi bers is less
uniform. Th ey are considered monoaminergic because
their cells of origin are generally associated with a single
neurotransmitter type: the locus coeruleus is noradren-
ergic, the raphe nucleus is serotinergic, and the tubero-
mammillary nucleus is histaminergic.
Now, show that all three fi bers innervate both the
deep cerebellar nuclei and cerebellar cortex.