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Lab 3 (ƒ5) - Somatosensory, Viscerosensory and Spinocerebellar Pathways

Spinocerebellar Pathways

There are three different pathways that carry proprioceptive information from the body to the cerebellum

1. The Posterior Spinocerebellar Pathway - Carries information from the lower body (S5 to T1) and enters the cerebellum via the inferior cerebellar peduncle
2. The Cuneocerebellar Pathway - Carries information from the upper body (C8 to C2) and also enters the cerebellum via the inferior cerebellar peduncle
3. The Anterior Spinocerebellar Pathway - Carries both unconscious proprioceptive and cutaneous information from the lower body (L5 to T12) and enters the cerebellum via the superior cerebellar peduncle.

Many of the 1° afferents conveying unconscious proprioceptive information from muscle and joint receptors in the body travel to the cerebellum in the posterior spinocerebellar and cuneocerebellar tracts, which remain ipsilateral throughout their entire extent. In the posterior spinocerebellar pathway, 1° afferents from the lower body make their first synapse in the dorsal nucleus of Clarke. As this nucleus is found only in cord segments L3 to C8, 1° afferents from lower segments must ascend in the gracile fasciculus to reach it. The posterior spinocerebellar 2° afferents ascend the cord uncrossed in the ipsilateral lateral funiculus as the posterior spinocerebellar tract. These 2° afferents join the inferior cerebellar peduncle and terminate in the ipsilateral cerebellum.

In the cuneocerebellar pathway, the 1° afferent fibers enter the cord in the cervical posterior roots, join the cuneate fasciculus in which they ascend to the lateral cuneate nucleus where they terminate. The axons of the 2° afferents, the cuneocerebellar tract, join the inferior cerebellar peduncle to travel to and terminate in the ipsilateral cerebellum.

In the anterior spinocerebellar pathway, 1° afferents conveying unconscious proprioceptive information from Golgi tendon organs and muscle spindle Group II fibers of the leg and trunk terminate on anterior horn neurons called spinal border cells. These cells, found at L5 to T12, also synapse with 1° cutaneous afferents, spinal interneurons, and descending tracts. The axons from the spinal border cells, 2° anterior spinocerebellar afferents, decussate and form the anterior spinocerebellar tract at the posterolateral border of the anterior funiculus. These fibers ascend to midbrain levels where they join the superior cerebellar peduncle and descend back down to the cerebellum. Before the anterior/ventral spinocerebellar tract fibers terminate, they decussate again and terminate in the cerebellum ipsilateral to the body part represented. Consequently, there is a double cross in this pathway, one at the level of the tract’s cells of origin, i.e., the spinal border cells, and a second one in the cerebellum.