16 Cerebellar connections

The arbor vitae is the cerebellar white matter, so called for its branched, tree-like appearance. In some ways it more resembles a fern and is present in both cerebellar hemispheres. It brings sensory and motor information to and from the cerebellum. The arbor vitae is located deep in the cerebellum. Situated within the arbor vitae are the deep cerebellar nuclei; the dentate, globose, emboliform and the fastigial nuclei. These four different structures lead to the efferent projections of the cerebellum.

Climbing fibers are the name given to a series of neuronal projections from the inferior olivary nucleus located in the medulla oblongata.

The dentatothalamic tract is a tract which originates in the dentate nucleus and follows the ipsilateral superior cerebellar peduncle, decussating later on and reaching the contralateral red nucleus and the contralateral thalamus.

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.

The juxtarestiform body is a subdivision of the inferior cerebellar peduncle, which comprises both the juxtarestiform and restiform bodies.

The middle cerebellar peduncles are paired structures that connect the cerebellum to the pons and are composed entirely of centripetal fibers, i.e. incoming fibers. The fibers arise from the pontine nucleus to the opposite hemisphere of the cerebellar cortex. The fibers are arranged in three fasciculi: superior, inferior, and deep.The superior fasciculus, the most superficial, is derived from the upper transverse fibers of the pons; it is directed backward and lateralward superficial to the other two fasciculi, and is distributed mainly to the lobules on the inferior surface of the cerebellar hemisphere and to the parts of the superior surface adjoining the posterior and lateral margins. The inferior fasciculus is formed by the lowest transverse fibers of the pons; it passes under cover of the superior fasciculus and is continued downward and backward more or less parallel with it, to be distributed to the folia on the under surface close to the vermis. The deep fasciculus comprises most of the deep transverse fibers of the pons. It is at first covered by the superior and inferior fasciculi, but crosses obliquely and appears on the medial side of the superior, from which it receives a bundle; its fibers spread out and pass to the upper anterior cerebellar folia. The fibers of this fasciculus cover those of the inferior cerebellar peduncle.

Mossy fibers are one of the major inputs to cerebellum. There are many sources of this pathway, the largest of which is the cerebral cortex, which sends input to the cerebellum via the pontocerebellar pathway. Other contributors include the vestibular nerve and nuclei, the spinal cord, the reticular formation, and feedback from deep cerebellar nuclei. Axons enter the cerebellum via the middle and inferior cerebellar peduncles, where some branch to make contact with deep cerebellar nuclei. They ascend into the white matter of the cerebellum, where each axon branches to innervate granule cells in several cerebellar folia.

The myoclonic triangle is an important feedback circuit of the brainstem and deep cerebellar nuclei which is responsible for modulating spinal cord motor activity.

The olivocerebellar tract, also known as olivocerebellar fibers, are neural fibers which originate at the olivary nucleus and pass out through the hilum and decussate with those from the opposite olive in the raphe nucleus, then as internal arcuate fibers they pass partly through and partly around the opposite olive and enter the inferior peduncle to be distributed to the cerebellar hemisphere of the opposite side from which they arise.

The pontocerebellar fibers are the second order neuron fibers of the corticopontocerebellar tracts that cross to the other side of the pons and run within the middle cerebellar peduncles, from the pons to the contralateral cerebellum.

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

In the human brain, the superior cerebellar peduncle is a paired structure of white matter that connects the cerebellum to the midbrain. It consists mainly of efferent fibers, the cerebellothalamic tract that runs from a cerebellar hemisphere to the contralateral thalamus, and the cerebellorubral tract that runs from a cerebellar hemisphere to the red nucleus. It also contains afferent tracts, most prominent of which is the ventral spinocerebellar tract. Other afferent tracts are the trigeminothalamic fibers, tectocerebellar fibers, and noradrenergic fibers from the locus coeruleus. The superior peduncle emerges from the upper and medial parts of the white matter of each hemisphere and is placed under cover of the upper part of the cerebellum.

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.