Which structure provides voluntary control over defecation?

The pudendal nerve is responsible for providing voluntary control over defecation. Specifically, it innervates the external anal sphincter, a muscle that plays a key role in maintaining continence and allowing for the voluntary expulsion of feces during defecation. When the rectum is filled, stretch receptors signal the need to defecate, and the individual can consciously choose to relax the external anal sphincter, which is under voluntary control due to pudendal nerve innervation.

The other structures mentioned do not play a direct role in voluntary control of defecation. The conus medullaris is the terminal end of the spinal cord, while the hypogastric nerve is more involved in the autonomic regulation of the bladder and gastrointestinal tract. The myenteric plexus is part of the enteric nervous system that regulates gut motility but does not provide voluntary control. Understanding the specific roles of these structures helps clarify why the pudendal nerve is essential for voluntary defecation.