Spinal cord distribution of the somatic innervation of the external urethral sphincter of the cat

Using retrograde degeneration, the motor neurons of the urethral branch of the pudendal nerve, which supplies the external urethral sphincter, were located in the ventral part of the ventral horn in the sacral spinal cord of the cat. Two cell groups, partially fused into one column could be delineated. The more rostral and lateral group was usually in the S₁ segment, while the more caudal and medial group was usually in the S₂ segment. Chromatolysis in dorsal root ganglia indicated that afferents were distributed in approximately the same way as efferents. Recording evoked responses from dorsal and ventral rootlets disclosed some variation with the column occasionally extending into the L₇ or S₃ segments. The center of the column was usually near the junction of S₁ and S₂, extending for approximately 2 segments. The separation which sometimes occurred in the middle of the column should be considered if microelectrode studies of these cells are attempted. The origin in the spinal cord of the urethral branch of the pudendal nerve overlaps the origin of the pelvic nerve to the detrusor in the S₂ segment in the cat.