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

Abstract

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.

A new approach to estimation of the number of central synapse(s) included in the H-reflex

“…In another study, Ertekin and coworker stimulated the tibial nerve and epidurally recorded the potentials. They proposed that the central conduction time of the soleus H-reflex could be about 1.1 msec[13]. The values of 1.3 and 1.1 msec that were obtained are close to the our value of 1.09 msec.…”

Reduced variance of latencies in pudendal evoked potentials after normalization for body height

“…The best fitting is obtained for k,/u, = 12.5*10--3 which is in accordance with the neuroanatomical data [Ertekin and Mungan, 1993; Jones et a]., 19821. Indeed the mean conduction velocity u, in the posterior columns of the sensory tracts of the spinal cord, is about 30 d s e c [Bradshaw, 19881 and the distance between the first and the second wave generators of the SEP (i.e., between the sacral dorsal horn and the thalamus) is about 0.40 of the body height (H) [Chu, 19861. The best fitting of the ON, latency in relation to height can be discussed in a similar way.…”

Neurophysiologic studies of the sacral reflex in women with “non‐neurogenic” sacral dysfunction

“…In men, afferent conduction from the dorsal nerves of the penis to the spinal cord took 9 msec, and efferent conduction from the spinal cord to the bulbocavernosus muscle, 13 msec 23. As similar values would also be expected in women, only extreme cauda equina and pudendal nerve demyelination (e.g., as found in some hereditary demyelinative neuropathies, or rarely with compressive cauda equina lesions) could cause 15–20 msec reflex latency delays in peripheral conduction.…”

“…Delays in central reflex conduction within the conus medullaris are a much more likely cause. The central course of the sacral reflex pathway has been estimated to include 5–6 consecutive synapses 23. The reason for delays in central reflex conduction might be either a weak or desynchronized afferent volley, or a reduced level of excitation of the spinal neurons.…”