Lab 5 - Somatosensory, Viscerosensory and Spinocerebellar Pathways

Spinocerebellar Pathway - Spinal Cord

The images move from the brainstem to the diencephalon. View and identify the structures in the illustration.

Sacral Cord

The posterior spinocerebellar 1° afferents that enter spinal cord segments below L3 (i.e., in posterior roots S5 to L2) ascend the cord in the ipsilateral gracile fasciculus.

Lumbar Cord

Most 1° afferents conveying unconscious proprioceptive information from muscle and joint receptors in the lower limbs and trunk travel in the gracile fasciculus to their site of destination -- the dorsal nucleus of Clarke (nucleus dorsalis)(L3-C8). The 2° afferents remain uncrossed and collect in the lateral funiculus as the posterior spinocerebellar tract.

The 1° afferents of the anterior spinocerebellar pathway are terminating on anterior horn neurons called spinal border cells (L5 to T12). The axons from the spinal border cells (2° afferents) decussate and form the anterior/ventral spinocerebellar tract at the posterolateral border of the anterior funiculus.

Thoracic Cord

The 1° posterior spinocerebellar afferents synapse in the dorsal nucleus of Clarke that is present at L3­C8. The 2° axons from the dorsal nucleus of Clarke travel to the ipsilateral lateral funiculus and ascend the spinal cord as the posterior/dorsal spinocerebellar tract. At this level, there are no 1° anterior spinocerebellar afferents or spinal border cells, which are only found at cord levels L5 to T12. However, the crossed axons of the spinal border cells, the 2° anterior spinocerebellar afferents, are ascending the cord in the anterior/ventral spinocerebellar tract.

Cervical Cord

At all or most cervical levels of the cord, the spinal border cells (L5 to T12) and the dorsal nucleus of Clarke (L3-C8) are absent. Consequently, the 1° afferents for unconscious proprioception from the upper extremities travel via the cuneatefasciculus to synapse in the lower medulla. The uncrossed 2° posterior spinocerebellar afferents originating from the dorsal nucleus of Clarke continue up the spinal cord in the posterior/dorsal spinocerebellar tract, while the crossed 2° anterior spinocerebellar afferents ascend in the anterior/ventral spinocerebellar tract.