Auditory System: Ear Anatomy, Hearing Theories, and Hearing Loss

Pinna

The visible part of the ear; collects sound waves.

Auditory Canal

Carries the sound to the eardrum (tympanic membrane).

Eardrum

Vibrates when sound hits it.

Ossicles

Three tiny bones — hammer (malleus), anvil (incus), and stirrup (stapes).

Function of Ossicles

Amplify and transfer vibrations from the eardrum to the inner ear.

Cochlea

A spiral, fluid-filled structure that contains hair cells (receptor cells for hearing).

Vibrations in Cochlea

Vibrations from the ossicles move the fluid inside the cochlea.

Basilar Membrane

The basilar membrane inside moves, bending the hair cells.

Hair Cells

The hair cells create neural impulses that travel along the auditory nerve → thalamus → auditory cortex (in temporal lobe).

Place Theory

Different pitches = different places on the basilar membrane vibrate.

Frequency Theory

The whole basilar membrane vibrates at the same rate as the sound wave.

Volley Principle

For mid-range sounds, neurons take turns firing in rapid succession.

Sound Localization

The brain compares timing and intensity differences between ears to locate sound sources.

Example of Sound Localization

If sound hits your left ear first and is louder there, it's coming from the left.

Hearing Loss

Conductive: Damage to outer or middle ear (e.g., ossicles). Sound can't reach cochlea efficiently.

Sensorineural Hearing Loss

Damage to cochlea or auditory nerve (often from loud noise or aging).