Amyotrophic Lateral sclerosis is characterized by

Harrison's principles of internal medicine 17th edition. *Pathologic hallmark is death of lower motor neurons (consisting of anterior horn cells in the spinal cord and their brainstem homologues innervating bulbar muscles) and upper, or coicospinal, motor neurons (originating in layer five of the motor coex and descending the pyramidal tract to synapse with lower motor neurons). Although at onset ALS may involve selective loss of only upper or lower motor neurons, it ultimately causes progressive loss of both