Intermediate latencies are probably due to stimulation to a branch point that then travels back to the muscle failing to complete the complete reflex arc at the spinal level. This variability in latency limits usefulness of measurement of this reflex. The awareness of the need to defecate or urinate occurs in the superior frontal gyrus and anterior cingulate gyrus. Rectal distention stimulates internal anal sphincter relaxation and the sampling reflex. If defecation is to be deferred voluntary contraction of the external anal sphincter and levator ani muscles occurs.
Accommodation refers to the relaxation of the rectal ampulla after an initial increase in pressure.
At the appropriate time for defecation or when rectal pressure is high, the levator ani muscle, puborectalis muscle and external anal sphincter relax. Pelvic floor relaxation, along with a squatting position, straightens the anorectal angle. An increase in abdominal pressure along with colonic and rectal contractions allows expulsion of a fecal bolus. Increased effort is necessary to expel a smaller bolus than an optimal 2-cm fecal bolus. The interplay of all the aforementioned anatomy and physiology ensures continence.