External anal sphincter is innervated by
**Core Concept**
The external anal sphincter is a striated muscle that plays a crucial role in maintaining continence. It is innervated by the autonomic and somatic nervous systems, which regulate its function and tone.
**Why the Correct Answer is Right**
The external anal sphincter is primarily innervated by the pudendal nerve, a branch of the sacral plexus (S2-4). The pudendal nerve carries both somatic motor fibers, which control voluntary contraction of the muscle, and autonomic fibers, which regulate the muscle's resting tone. This dual innervation allows for precise control over the external anal sphincter, enabling voluntary contraction and relaxation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the inferior rectal nerve, a branch of the pudendal nerve, primarily innervates the internal anal sphincter.
**Option B:** This option is incorrect because the superior rectal nerve, a branch of the inferior mesenteric plexus, primarily innervates the internal anal sphincter.
**Option C:** This option is incorrect because the pelvic splanchnic nerves, branches of the S2-4 spinal nerves, primarily innervate the pelvic floor muscles, including the levator ani and coccygeus muscles.
**Clinical Pearl / High-Yield Fact**
The pudendal nerve is often damaged during childbirth, leading to anal incontinence and fecal leakage. This highlights the importance of preserving the pudendal nerve during surgical procedures and childbirth.
**Correct Answer: C. Pelvic splanchnic nerves.