ANTIDROMIC POTENTIAL RECORDINGS FROM THE BULBAR PYRAMID OF THE CAT

Abstract

Antidromic activity initiated by stimulation of corticospinal fibers at cord levels has been recorded from the bulbar pyramids of the cat. Data are presented indicating that conduction velocities in the pyramidal system vary from 164 m./sec. down to or lower than 1.8 m./sec. In terms of voltage developed, the major response is conducted at velocities which range from 35 to 60 m./sec. The lateral, corticospinal tract in the cat descends at least to the 6th lumbar segment. Its size diminishes abruptly in the lower cervical and upper thoracic segments of the spinal cord. The size-number relationships of the fibers of the bulbar pyramid are presented. Fibers range in size from 12.5 microns to less than 1 micron, the great majority lying in the range between 1 and 4 microns. The anatomical and functional evidence indicates that no grouping or segregation of similar sizes and conduction velocities exists in the pyramid such as exists in some peripheral nerves.