Mechanism of Hearing (4 Marks)

1. Sound waves enter the external auditory meatus and cause the ear drum to vibrate.
2. Auditory ossicles amplify and transmit vibrations to the stapes, which moves the oval window - transmitting vibrations to the perilymph of scala vestibuli.
3. Vibrations pass through the vestibular (Reissner's) membrane into the endolymph of the cochlear duct - causing up and down movements of the Basilar Membrane (BM).
4. This pulls and moves hair cells sideways, causing depolarization of receptor cells - the membrane becomes more permeable to calcium ions.
5. Calcium ions trigger neurotransmitter release from vesicles at the base of receptor cells, stimulating sensory neurons.
6. Sensory impulses travel along the cochlear branch of the vestibulocochlear nerve to the auditory cortex of the temporal lobe for perception/interpretation.