Below the brainstem is the elongated, segmented spinal cord and its associated dorsal and ventral roots which merge to form spinal nerves. Some disorders are confined to the spinal cord while others may include its roots; injuries to these structures produce a number of distinctive syndromes. The features of spinal cord disorders reflect its anatomy and physiology, i.e., ascending sensory tracts, descending motor systems, sensory afferent fibers and the nuclei receiving incoming sensory information, nuclei giving rise to exiting motor fibers, and the reflexes which result from the interaction of all these elements.
1) Dorsal roots feed a variety of sensory fibers carrying information to synapse in the dorsal gray horn nuclei and form the ascending pathways, e.g., nucleus proprius and Clarke's column; some fibers ascend without synapsing: ascending pathways include:
a) the posterior white column - conscious proprioception, discriminative touch and vibratory sense - fibers ascend uncrossed without synapsing.
b) the anterior and lateral spinothalamic tracts - after synapsing in the nuclei of the dorsal gray horn, pain, temperature and light touch fibers cross in the anterior white commissure to ascend.
c) the posterior spinocerebellar tract - "unconscious" proprioception from the lower extremity, incoming fibers synapse in Clarke's column of the dorsal gray horn and ascend without crossing; upper extremity fibers ascend uncrossed without synapsing, in the posterior white column, to finally synapse in the ipsilateral accessory cuneate nucleus of the medulla.
2) Ventral roots from all spinal cord segments carry fibers from anterior horn cells to control voluntary muscle. Ventral roots from thoracolumbar and sacral regions also carry preganglionic autonomic fibers from cells of the intermediate gray for control of the viscera.
a) the lateral corticospinal tract (along with the lateral reticulospinal tract) helps control the anterior horn cells for skeletal muscle volitional motor activity.
b) the lateral vestibulospinal tract (along with the medial reticulospinal tract) helps control the anterior horn cells and are especially important in the reflex control of skeletal muscle.
c) descending autonomic fibers descend (mixed with the lateral corticospinal tract) for the control of the preganglionic autonomics responsible for visceral functions.