Expansion
Dorsal columns behind, corticospinal laterally, spinothalamic anterolaterally
Expansion
Ascending
- Dorsal columns (posterior): fine touch, vibration, proprioception. Gracilis medially for the legs, cuneatus laterally for the arms. Decussate in the medulla
- Spinothalamic (anterolateral): pain and temperature. Decussate within one or two segments of entry
- Spinocerebellar: unconscious proprioception, uncrossed
Descending
- Lateral corticospinal: voluntary motor, decussated in the medullary pyramids
- Anterior corticospinal: uncrossed until the segmental level
Somatotopy in the corticospinal tract runs from cervical medially to sacral laterally, which explains two syndromes:
- Central cord syndrome: a central lesion affects medial fibres first, giving arms weaker than legs, typically after hyperextension injury in a spondylotic neck
- Extrinsic compression affects lateral fibres first, so sacral segments are involved early, giving early bladder involvement and sacral sensory loss
The cord ends at L1 to L2 in the adult, below which the cauda equina gives lower motor neurone signs rather than upper.