Summary
Highlights
The outer ear consists of the pinna, which protects the inner ear and helps locate sound sources, and the external auditory meatus (ear canal), which collects and directs sound to the eardrum.
The middle ear is an air-filled cavity containing the eardrum (tympanic membrane), ossicles (malleus, incus, stapes), and the Eustachian tube. Sound waves vibrate the tympanic membrane, which in turn moves the ossicles, transferring energy to the inner ear.
The inner ear has two parts: the vestibular portion for balance and the auditory portion (cochlea) for hearing. The vestibular portion includes semicircular canals, ampullae, utricle, and saccule, which contain fluid and sensory cells that respond to head movements to maintain balance.
The cochlea is a coiled tube, approximately 35-40mm long when uncoiled, wrapped around the auditory nerve. It's divided into three sections: the scala vestibuli and scala tympani (containing perilymph fluid) and the scala media (containing endolymph fluid).
Along the basilar membrane within the cochlea are outer and inner hair cells, arranged by frequency detection and covered by the tectorial membrane. When sound energy vibrates the basilar membrane, the stereocilia on the hair cells bend, opening ion gates and creating electrical charges. These charges form neural impulses that travel along the auditory nerve to the brain, where they are interpreted as sound.