The intramural pelvic nerves of the dog colon were studied morphologically and electrophysiologically. These nerves emanate from the pelvic plexus, and ascend between the muscle layers along 57.5% of the colon's length. Many thin branches connect with Auerbach's plexus. Most of the nerves responded bilaterally with compound action potentials of A delta and C fibres to stimulation of the sacral dorsal roots, and with those of C fibres to stimulation of the ventral roots. Mean conduction velocities of the A delta and C fibres were 9.0 and 0.9 m/s, respectively. Distension of a section of colon at up to 85.0% of the length of the colon from the anus activated afferent fibres, and electrical stimulation of points at up to 102% of this length elicited responses in efferent fibres. In dogs in which the continuity of the colonic wall was interrupted by a ligature but the nerves were left intact, the intramural pelvic nerves were found to convey centrifugal activities of the recto‐ and ano‐colonic reflexes to the proximal colon, and centripetal and centrifugal activities of the colo‐colonic reflex.
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