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Lab 5, Page 18 of 26
The first set of images are from the brainstem to the diencephalon. Moving to the next section (moving to the right through the images) is moving rostrally. At each level read the corresponding section of text and identify the bold structures.
More content below images.
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.
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.
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.
At all or most cervical levels of the cord, the spinal border cells (L5 to T12) and the dorsal nucleus of Clarke (L3C8) are absent. Consequently, the 1° afferents for unconscious proprioception from the upper extremities travel via the cuneate fasciculus 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.
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