What happens during hair-cell transduction?

• A. Calcium channels open leading to hyperpolarization
• B. Hair cells vibrate without transduction
• C. Endolymph flows to generate action potentials
• D. Mechanical energy causes potassium channels to open, leading to depolarization and neurotransmitter release

Answer: (D)

Mechanical deflection of the hair bundle opens mechanosensitive channels that are permeable to potassium and calcium. In the endolymph, which surrounds the hair cells, potassium concentration is high and the potential is positive. When the channels open, potassium flows into the hair cell, depolarizing it. This depolarization then opens voltage-gated calcium channels, calcium enters, and neurotransmitter is released onto the afferent nerve fibers. This sequence converts the mechanical energy of sound into an electrical signal that the nervous system can use. The other ideas don’t fit because transduction is not just a vibration without electrical change, endolymph flow doesn’t directly generate action potentials, and calcium channels participate after depolarization to trigger release rather than initiating a hyperpolarizing event.