Okay, let's tackle this question step by step. The question is about the nerve responsible for pain in external hemorrhoids during bowel movements. First, I need to recall the innervation of the anal region. The anal canal is divided into the upper and lower parts. The upper part is innervated by the autonomic nervous system, which doesn't have pain sensation. The lower part, including the external anal sphincter and surrounding skin, is innervated by somatic nerves.

External hemorrhoids are located in the lower anal canal, so their pain should be mediated by somatic nerves. The major nerves in this area are the pudendal nerve and the sympathetic nerves. The pudendal nerve splits into the inferior rectal nerve, which provides sensory innervation to the perianal skin. The inferior rectal nerve is part of the pudendal nerve's distribution.

The options might include the inferior rectal nerve, superior rectal nerve, and others. The superior rectal nerve is part of the autonomic system and innervates the upper anal canal, which is why internal hemorrhoids don't cause pain unless there's thrombosis or other complications. The inferior rectal nerve, being somatic, would be responsible for the pain in external hemorrhoids.

So the correct answer should be the inferior rectal nerve, which is a branch of the pudendal nerve. The other options like the superior rectal nerve (autonomic) or the hypogastric plexus (sympathetic) don't innervate the external anal region. The perineal nerve is a branch of the pudendal but innervates different areas. Therefore, the correct answer is the inferior rectal nerve.

**Core Concept**
The anal canal's sensory innervation is divided: the upper two-thirds (internal hemorrhoids) are autonomic (no pain sensation), while the lower third (external hemorrhoids) is somatic, mediated by the inferior rectal nerve. Pain from external hemorrhoids arises due to somatic nerve stimulation during defecation.

**Why the Correct Answer is Right**
The inferior rectal nerve, a terminal branch of the pudendal nerve (S2-S4), provides sensory innervation to the perianal skin and external anal sphincter. During defecation, mechanical stretch or irritation of external hemorrhoids activates nociceptors in this nerve, transmitting pain signals via the pudendal pathway. This explains the localized, sharp pain characteristic of external hemorrhoids.

**Why Each Wrong Option is Incorrect**
**Option A:** *Superior rectal nerve* – Incorrect. It is a visceral autonomic nerve (sympathetic and parasympathetic fibers) innervating the upper anal canal and rectum. It lacks pain fibers and does not transmit sensory signals.
**Option C:** *Perineal nerve* – Incorrect. While a branch of the pudendal nerve, it innervates the perineum and external genitalia, not the anal margin.
**Option D:** *Hypogastric plexus* – Incorrect. This sympathetic plexus supplies visceral structures in the pelvis but does not mediate somatic pain from external hemorrhoids.

**Clinical Pearl / High-Yield Fact**
External hemorrhoids cause *pain during defecation* due to somatic innervation by the **

✓ Correct Answer: B. Pudendal nerve