**Core Concept**
The question is testing the knowledge of the autonomic innervation of the anal canal, specifically the nerves responsible for transmitting pain from the anal region. The anal canal receives its innervation from the autonomic nervous system, with the sympathetic and parasympathetic divisions playing a crucial role in regulating its function.

**Why the Correct Answer is Right**
The pain experienced by a patient with external hemorrhoids while passing stools is mediated by the pudendal nerve. The pudendal nerve is a branch of the sacral plexus that arises from the S2, S3, and S4 nerve roots. It provides sensory innervation to the perianal skin, including the external anal sphincter, and is responsible for transmitting pain from the anal region to the spinal cord. The pudendal nerve also plays a crucial role in the control of the external anal sphincter, which helps to regulate defecation.

**Why Each Wrong Option is Incorrect**
**Option A:** The superior rectal nerve is not responsible for transmitting pain from the anal region. It is a branch of the inferior mesenteric plexus that provides parasympathetic innervation to the rectum and is involved in the regulation of defecation.

**Option B:** The inferior hypogastric plexus is a network of nerves that provides sympathetic innervation to the pelvic organs, including the rectum and bladder. However, it is not directly responsible for transmitting pain from the anal region.

**Option C:** The rectal nerve is a branch of the inferior hypogastric plexus that provides sensory innervation to the rectum. However, it is not primarily responsible for transmitting pain from the anal region.

**Clinical Pearl / High-Yield Fact**
The pudendal nerve is also responsible for transmitting sensation from the perianal skin, including the sensation of itching and discomfort. This is an important consideration in patients with anal pain or discomfort, as it can help guide the diagnosis and treatment of underlying conditions.

**Correct Answer:** C. The pudendal nerve is responsible for transmitting pain from the anal region to the spinal cord.