The Morphological Properties of the Corticospinal (Pyramidal) Tract in Various Mammalian Species

Abstract

Corticospinal tract projects directly from cerebral cortex to spinal cord and it is found only in the brains of mammals. This system is responsible for voluntary and fine movements in the body. Corticospinal tract originates from pyramidal neurones which cell body is located in layer V of the cerebral sensorymotor cortices. Soma diameters of the pyramidal neurones increase gradually from primitive mammals to human. In the majority of the mammalian species the pyramidal tracts decussate in the lower medulla oblongata, prior to their descend into the spinal cord. The total number of fibers (myelinated + unmyelinated) in each medullary pyramid are 192,000 in rabbit, 243,000 in rat, 450,000 in cat, 400,000 in monkey, and 1,000,000 in man. The diameters of these fibers have a range from 0.05 μm-20 μm. Corticospinal fibers terminate on the sensory neurones of dorsal horn, neurones of intermediate zone, and motor neurones of ventral horn, of the spinal grey matter. There is close relationship between line movements of extremities and direct monosynaptic corticomotoneuronal connections.