Spatial organization of direct connections of the sensomotor cortex with the rhombencephalon and spinal cord in the cat

Abstract

The distribution and ultrastructure of terminals of corticofugal fibres in the cat hindbrain and spinal cord were examined by light and electron microscopy in various periods of experimental degeneration elicited by large or small sensorimotor cortex destructions. Using the Fink-Heimer technique, it is shown that the corticofugal projections in the dorsal column nuclei and in the spinal intermediate zone are somatotopically arranged. Even small restricted areas of sensorimotor cortex give two separate descending supraspinal systems. The fibres of the first system are distributed in the dorsolateral and dorsolmedial parts of the spinal intermediate zone, predominantly contralaterally. The fibres of the second system are distributed in the dorsolateral and ventromedial parts of the intermediate zone (bilaterally). Degenerating axo-somatic and axo-dendritic contacts contain spherical vesicles. The majority of degenerating axons in n. cuneatus are 0.5-1,5 mu in diameter. The data obtained are discussed in connection with the electrophysiological data on the mechanisms of the cortical control of the spinal cord neuronal activity.