Sacral spinal cord and root potentials evoked by the stimulation of the dorsal nerve of penis and cord conduction delay for the bulbocavernosus reflex

Segmental spinal cord and root potentials in response to stimulations of the dorsal nerve of penis, tibial nerve, and the sural nerve were epidurally recorded in normal subjects. EMG responses from the bulbocavernosus (BC) and the various leg muscles were also recorded in response to bipolar stimulations by the same epidural needle electrodes of the sacral cord and lumbosacral roots. The afferent conduction velocity from the penis to Th₁₂-L₁ intervertebral level was about 40 m/sec on the average, which is significantly slower than those obtained by the stimulation of the mixed and cutaneous nerves at the lower limb. The latency of the motor responses of the BC muscle from Th₁₂-L₁ spine levels were found comparatively longer than those of thigh muscles on maximal epidural stimulation in spite of the shorter distances to the BC muscle. The central conduction delay within the sacral cord of the bulbocavernosus reflex was calculated and found to be about 8.2 msec, while the central conduction time was about 1.1 msec for the Soleus-H-Reflex. These findings may suggest that there may be about 5–6 synapsis necessary for the first component of the bulbocavernosus reflex, though some faster oligosynaptic cord linkage may also exist.