Final answer:
The primary role of outer hair cells is to amplify the sound vibrations within the cochlea. They enhance cochlear fluid movement, which increases the basilar membrane's motion, thus amplifying sound signals before they are converted into electrical impulses by the inner hair cells.
Step-by-step explanation:
The major role of outer hair cells within the ear is to amplify sound vibrations in the cochlea, making choice 1) the correct answer. When sound waves enter the ear through the ear canal, they strike the eardrum and make it vibrate. These vibrations are then transferred through the small bones of the middle ear to the cochlea, a fluid-filled structure in the inner ear.
The cochlea contains tiny hair cells, which are mechanoreceptors that bend in response to these vibrations. The outer hair cells number approximately 12,000 and their primary function is to fine-tune and amplify incoming sound waves. This is done by the outer hair cells changing length in response to sound stimuli, which enhances the movement of the cochlear fluid and thereby increases the movement of the basilar membrane. This action significantly amplifies the sound signal before it is transformed into electrical signals by the inner hair cells.
The amplified vibrations cause the bending of stereocilia on the hair cells, initiating an electrical signal that is sent to the auditory nerve, and eventually to the brain, where it is interpreted as sound.