Hair cells in the vestibular system fire more action potentials when the hair: (A) is bent in a specific direction. (B) vibrates at a specific frequency. (C) is moved with a specific force. (D) cells remain motionless.
The correct answer and explanation is:
The correct answer is (A) is bent in a specific direction.
Explanation:
Hair cells in the vestibular system are specialized sensory receptors that detect head movements and help maintain balance and spatial orientation. These hair cells have hair-like projections called stereocilia. When the head moves, the fluid within the vestibular apparatus moves as well, causing the stereocilia to bend.
The key point is that the bending of these stereocilia in a specific direction alters the rate at which the hair cells fire action potentials. If the stereocilia bend toward the tallest stereocilium (kinocilium), ion channels open, causing depolarization of the hair cell. This depolarization leads to an increase in the release of neurotransmitters onto the afferent neurons, which then fire more action potentials. Conversely, if the stereocilia bend away from the kinocilium, the hair cell hyperpolarizes, decreasing neurotransmitter release and reducing action potential firing.
This directional sensitivity allows the vestibular system to precisely detect the direction and magnitude of head movements. The bending itself is critical; mere vibration, force, or remaining still will not necessarily increase action potentials unless it causes bending in the preferred direction.
Option (B), vibration at a specific frequency, is more relevant to hair cells in the auditory system (cochlea) that detect sound, not the vestibular system.
Option (C), movement with a specific force, is less precise because it is the bending direction, rather than force magnitude alone, that determines the response.
Option (D), cells remaining motionless, would lead to a baseline or resting firing rate, not an increase.
In summary, the vestibular hair cells respond by increasing action potential firing rates when their stereocilia bend in a specific direction, allowing the brain to interpret head movement and maintain balance.