**Core Concept**
The ampulla of the semicircular canals in the vestibular system is a critical structure for detecting rotational movements and maintaining balance. The sensory organ within the ampulla is responsible for transducing mechanical stimuli into electrical signals that are interpreted by the brain.

**Why the Correct Answer is Right**
The correct answer is the **crista ampullaris**. It is a specialized sensory organ within the ampulla that contains **hair cells**, which are embedded in a gelatinous matrix called the **cupula**. When the head rotates, the fluid within the semicircular canal lags behind, causing the cupula to bend and stimulate the hair cells. This bending of the hair cells triggers a mechanical response in the stereocilia, leading to the opening of mechanically gated ion channels and the generation of an action potential.

**Why Each Wrong Option is Incorrect**
* **Option A:** The **macula** is a sensory organ found in the otolith organs (utricle and saccule) and is responsible for detecting linear acceleration and gravity, not rotational movements.
* **Option B:** The **basilar membrane** is a structure within the cochlea that plays a crucial role in sound processing and hearing, but it is not related to the ampulla or rotational movements.
* **Option C:** The **vestibular nerve** is the nerve that carries sensory information from the vestibular system to the brain, but it is not a sensory organ itself.

**Clinical Pearl / High-Yield Fact**
The vestibular system is responsible for detecting rotational movements and maintaining balance. Damage to the vestibular system can result in vertigo, dizziness, and loss of balance.

**Correct Answer:** C. Crista ampullaris.