VESTIBULOCEREBELLUM
The vestibulocerebellum receives afferent fibers from the vestibular ganglion and from the
vestibular nuclei of the same side.Some of the afferent fibers from these sources terminate in the
fastigial nucleus, which also receives collateral branches of the axons destined for the cortex of
the vestibulocerebellum. The vestibulocerebellum also receives afferents from the contralateral
accessory olivary nuclei. These fibers have collateral branches to the fastigial nucleus and end as
climbing fibers in the cortex of the flocculonodular lobe.
Some Purkinje cell axons from the vestibulocerebellar cortex proceed to the brain stem (an
exception to the general rule that such fibers end in central nuclei), but most terminate in the
fastigial nucleus. Fibers from the cortex and the fastigial nucleus traverse the inferior cerebellar
peduncle to their termination in the vestibular nuclear complex and in the central group of
reticular nuclei.
In summary, the vestibulocerebellum influences motor neurons through the vestibulospinal tract,
the medial longitudinal fasciculus, and reticulospinal fibers. It is concerned with adjustment of
muscle tone in response to vestibular stimuli. It coordinates the actions of muscles that maintain
equilibrium and participates in other motor responses, including those of the eyes, to vestibular
stimulation (see Chapter 22). The posterior vermis also contributes to the cerebellar control of
eye movements.
SPINOCEREBELLUM
The following four afferent systems project to the spinocerebellar cortex.
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Somatic sensory systems. The dorsal and ventral spinocerebellar tracts convey data from
proprioceptive endings and from touch and pressure receptors (Fig. 10-14). The dorsal
tract, consisting of the axons of the neurons constituting the nucleus thoracicus in spinal
segments T1 to L3 or L4, conveys information from the trunk and leg. The ventral tract,
which arises in various parts of the lumbosacral gray matter (see Chapter 5), is mainly
involved in conduction from the leg. Cuneocerebellar fibers from the accessory cuneate
nucleus (see Chapter 7) are equivalent, for the arm and neck, to those of the dorsal
spinocerebellar tract. Most of the fibers afferent to the cells of origin of the
spinocerebellar and cuneocerebellar tracts have ascended into the dorsal funiculi of the
spinal cord. All three trigeminal sensory nuclei (see Chapter 8) contain some neurons that
project to the spinocerebellum. These are functionally equivalent to the spinocerebellar
and cuneocerebellar projections, except for the head.
Precerebellar reticular nuclei. Modified data from cutaneous receptors are carried by
spinoreticular fibers to the lateral and paramedian reticular nuclei (see Figs. 9-1 and 9-2),
which project to the cerebellum. These two precerebellar reticular nuclei also receive
afferent fibers from primary motor and sensory areas of the cerebral cortex. Another
precerebellar reticular nucleus that projects to the vermis and medial parts of the
hemispheres is the reticulotegmental nucleus in the pons (see Fig. 9-1). This nucleus
receives afferents from the cerebral cortex and from the vestibular nuclei (see Fig. 1013).
Inferior olivary complex. The accessory olivary nuclei (in which spino-olivary tracts
terminate) project to the spinocerebellum. The olivocerebellar fibers end as climbing
fibers in the cortex.
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Special senses. Tectocerebellar fibers arise in the superior and inferior colliculi of the
midbrain, which are parts of the visual and auditory pathways, respectively.
Collateral branches of the axons from all the various afferent sources terminate in the interposed
nuclei, which also receive a small contingent of fibers from the red nucleus
The spinocerebellar cortex projects to the fastigial nucleus (from the vermis) and to the
interposed (globose and emboliform) nuclei (from the paravermal zones of the hemispheres).
Synergy of muscle action and control of muscle tone are effected in part through fastigiobulbar
connections, as described for the vestibulocerebellum. Axons from the interposed nuclei traverse
the superior cerebellar peduncle and terminate in the central group of reticular nuclei. Thus, the
spinocerebellum may influence motor neurons through reticulospinal fibers and a similar
projection to motor nuclei of cranial nerves. Alpha and gamma motor neurons are involved in
cerebellar control of muscle action, and the influence of the spinocerebellum on the skeletal
musculature is ipsilateral.
Some axons from the interposed nuclei traverse the superior cerebellar peduncle and end in the
red nucleus, which, in turn, projects to the inferior olivary nucleus. Others pass through or
around the red nucleus and continue to the ventral lateral nucleus of the thalamus, which projects
to the primary motor area of the cerebral cortex.
In summary, the spinocerebellum receives information from proprioceptive and exteroceptive
sensory endings and, indirectly, from the cerebral cortex. Visual and auditory input to areas of
the spino- and pontocerebellar cortex also takes place. These data are processed in the circuitry
of the cerebellar cortex, which modifies and refines the discharge of signals from the central
nuclei. Motor neurons are influenced mainly through relays in the vestibular nuclei, the reticular
formation, and the primary motor area of the cerebral cortex. The end result is control of muscle
tone and synergy of collaborating muscles, as appropriate at any moment for the adjustment of
posture and in many types of movement, including those of locomotion.
PONTOCEREBELLUM
Pontocerebellar fibers constitute the whole of the middle cerebellar peduncle. They originate in
the pontine nuclei (nuclei pontis) of the opposite side. Pontocerebellar axons have branches that
synapse with neurons in the dentate nucleus, and they are distributed throughout the cortex of the
cerebellar hemispheres and the superior vermis of the posterior lobe. The corticopontine tracts
originate in widespread areas of the contralateral cerebral cortex (especially that of the frontal
and parietal lobes but also temporal and occipital) and end in the pontine nuclei. Through the
corticopontine and pontocerebellar projections, the cortex of a cerebellar hemisphere receives
information concerning volitional movements that are anticipated or in progress. Some of the
pontine nuclei receive afferents from the superior colliculus and relay data used by the
cerebellum in the control of visually guided movements.
In addition to pontine afferents, the superior vermis of the posterior lobe, similar to the
spinocerebellar cortex, receives tectocerebellar fibers from the superior and inferior colliculi.
There are also olivary afferents, the axons of cells in the contralateral inferior olivary nucleus.
Purkinje cell axons from the pontocerebellar cortex terminate in the dentate nucleus, the efferent
fibers of which compose most of the superior cerebellar peduncle. After traversing the
decussation of the peduncles, some dentatothalamic fibers give off branches to the red nucleus,
but the majority passes through or around the red nucleus and end in the ventral lateral nucleus
of the thalamus. In turn, this thalamic nucleus projects to the primary motor area of cerebral
cortex in the frontal lobe. Through these connections, the pontocerebellum can modify activity in
corticospinal, corticoreticular, and reticulospinal pathways