**Core Concept:**

The pudendal nerve is a mixed sensory and motor nerve that plays a crucial role in the innervation of the genitourinary system, particularly the muscles of the external anal sphincter, the internal anal sphincter, and the smooth muscles of the urethra and bladder neck. The pudendal nerve originates from the sacral plexus, specifically from S2, S3, and S4 spinal nerves.

**Why the Correct Answer is Right:**

The correct answer to this question is S3. The pudendal nerve has three roots: S2, S3, and S4. These roots are part of the sacral plexus, which is formed by the reunion of preganglionic fibers from the sacral spinal cord segments in the sacral spinal cord. Among these roots, S3 is responsible for supplying the sphincter of the bladder, which is the primary focus of this question.

**Why Each Wrong Option is Incorrect:**

A. S2 is incorrect because it supplies the anal sphincter and the external anal sphincter.
B. S4 is incorrect because it supplies the anal sphincter and the internal anal sphincter, not the sphincter of the bladder.
C. S4 is incorrect as mentioned above, it supplies the anal sphincter and the internal anal sphincter, not the sphincter of the bladder.

**Clinical Pearl:**

Understanding the anatomy and function of the sacral spinal cord segments is essential for medical students, residents, and practicing physicians. Knowledge of the pudendal nerve and its roots is crucial for diagnosing and treating conditions related to pelvic floor dysfunction, urinary incontinence, and erectile dysfunction.

**Correct Answer:** S3