## Core Concept
The detection of rotational acceleration is a critical function of the **vestibular system** in the inner ear. This system is essential for maintaining balance and spatial orientation. The vestibular apparatus consists of the otolith organs (utricle and saccule) and the **semicircular canals**, which are filled with a fluid called endolymph and lined with sensory hair cells.

## Why the Correct Answer is Right
The correct answer, , corresponds to the **semicircular canals**. These structures are specifically designed to detect rotational movements of the head. When the head rotates, the fluid in the semicircular canals lags behind due to inertia, bending the sensory hair cells. This bending of hair cells triggers a signal that is transmitted to the brain, indicating the direction and speed of rotation. The semicircular canals are oriented at right angles to each other, allowing them to detect rotations in three-dimensional space.

## Why Each Wrong Option is Incorrect
* **Option A:** The **utricle** and **saccule** (otolith organs) are primarily responsible for detecting linear acceleration and changes in head position relative to gravity, not rotational acceleration.
* **Option B:** This option might refer to other parts of the inner ear or vestibular system not directly involved in detecting rotational acceleration.
* **Option D:** This could refer to other sensory organs or structures not related to the detection of rotational movements.

## Clinical Pearl / High-Yield Fact
A key clinical correlation is the **nystagmus** that occurs after rotational stimulation, which is a result of the vestibular system's response to rotational acceleration. This phenomenon is often tested in clinical settings to assess vestibular function. Remember, the **caloric test**, which involves irrigation of the ear canal with warm or cold water, also assesses vestibular function by inducing nystagmus.

## Correct Answer Line
**Correct Answer: C. Semicircular canals.**