Injury to the inferior rectal nerve results in paralysis of which muscle?

The inferior rectal nerve is a branch of the pudendal nerve, which plays a critical role in innervating the external anal sphincter. This muscle is under voluntary control and is responsible for maintaining fecal continence, allowing an individual to relax or tighten the anal opening during defecation.

When there is an injury to the inferior rectal nerve, it leads to paralysis of the external anal sphincter, which impairs the ability to control bowel movements. This can result in incontinence or difficulty in controlling the passage of stool, highlighting the importance of this nerve in maintaining anal function.

In contrast, the internal anal sphincter is under involuntary control and is primarily regulated by autonomic nerves rather than the inferior rectal nerve. The pelvic diaphragm and pelvic floor muscles, while also important for pelvic support and function, are not directly affected by damage to the inferior rectal nerve. Therefore, paralysis of the external anal sphincter is the direct consequence of an injury to this specific nerve.