What triggers the release of neurotransmitter in hair cells?

What triggers the release of neurotransmitter in hair cells?

• A. Influx of potassium ions through mechanically gated channels leads to depolarization.
• B. Hyperpolarization due to chloride movement.
• C. Hyperpolarization due to potassium efflux.
• D. Activation of voltage-gated sodium channels without depolarization.

Answer: (A)

The key idea is that transmitter release from hair cells is driven by depolarization caused by potassium entry through mechanically gated channels. When the hair bundle is displaced, these channels open and, because the endolymph is rich in potassium, potassium flows into the hair cell. This inward K+ current depolarizes the cell, which then opens voltage-gated calcium channels at the base. The resulting calcium influx triggers exocytosis of neurotransmitter (glutamate) onto the afferent spiral ganglion neurons. Hyperpolarization from chloride movement or potassium efflux would reduce release, and activation of voltage-gated sodium channels without depolarization wouldn’t initiate the release pathway.

The key idea is that transmitter release from hair cells is driven by depolarization caused by potassium entry through mechanically gated channels. When the hair bundle is displaced, these channels open and, because the endolymph is rich in potassium, potassium flows into the hair cell. This inward K+ current depolarizes the cell, which then opens voltage-gated calcium channels at the base. The resulting calcium influx triggers exocytosis of neurotransmitter (glutamate) onto the afferent spiral ganglion neurons. Hyperpolarization from chloride movement or potassium efflux would reduce release, and activation of voltage-gated sodium channels without depolarization wouldn’t initiate the release pathway.