Tone of the anal sphincter in maintained by: (A) Nervi erigentes, (B) Inferior hypogastric plexus, (C) Inferior rectal nerve, (D) Pelvic splanchnic nerves
Answer is C. The anal sphincters and puborectalis are the primary muscles responsible for continence. There are two sphincters: the internal anal sphincter, and the external anal sphincter. The internal sphincter is responsible for 85% of the resting muscle tone and is involuntary. ref - BDC 6e vol2 pg413-416