**Core Concept**
The cochlea is a spiral-shaped structure within the inner ear responsible for sound processing and transmission of auditory signals to the brain. The cells within the cochlea play a crucial role in converting mechanical sound waves into electrical signals.

**Why the Correct Answer is Right**
The correct answer refers to the specialized sensory cells within the cochlea known as **hair cells**. These cells have hair-like projections (stereocilia) that move in response to sound waves, triggering a mechanical signal that is converted into an electrical signal by the **transduction complex**. This electrical signal is then transmitted to the auditory nerve and eventually to the brain for sound interpretation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as it does not describe a type of cell found in the cochlea.

**Option B:** This is incorrect because **pillar cells** are supporting cells found in the cochlea, but they are not the primary sensory cells responsible for sound transduction.

**Option C:** This is incorrect because **Deiters cells** are also supporting cells found in the cochlea, but they do not play a direct role in sound transduction.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that hair cell damage or loss can lead to permanent hearing impairment, emphasizing the importance of protecting the inner ear from loud noises and ototoxic substances.

**Correct Answer:** C. **Hair cells**