Final answer:
The bending of hair cells due to pressure waves from sound increases calcium permeability, leading to membrane depolarization and subsequent neurotransmitter release, which triggers action potentials in sensory neurons for auditory signal transmission to the brain.
Step-by-step explanation:
When pressure from sound waves bends the membrane of the cochlear duct at a point of maximum vibration, hair cells located on the basilar membrane vibrate. The bending of these hair cells, specifically their stereocilia, opens mechanically gated ion channels, leading to an increase in membrane permeability to calcium. This causes the hair cell membrane to depolarize, initiating transduction of the auditory signal.
After depolarization, these hair cells release an excitatory neurotransmitter into a synapse with a sensory neuron. This leads to the generation of action potentials in the neuron, thereby transmitting auditory information to the central nervous system through the auditory nerve. The cochlear branch of the vestibulocochlear cranial nerve is responsible for sending this hearing information to the brain. Therefore, the increased calcium permeability resulting from the bending of the hair cells directly links the mechanical energy of sound waves to the electrical signals interpreted by the brain as sound.