Audition

Audition

The special sense of hearing; transduction of sound waves into a neural signal

Auricle (Pinna)

The outer, visible part of the ear that collects sound waves

External Ear

Contains the auricle, ear canal, and tympanic membrane

Middle Ear

Contains the ossicles; connected to the pharynx by the Eustachian tube

Inner Ear

Contains the cochlea (for audition) and the vestibule (for equilibrium)

Tympanic Membrane (Eardrum)

Membrane at the end of the ear canal that vibrates in response to sound waves

Ossicles

The three smallest bones in the body located in the middle ear; amplify incoming pressure waves and transmit them to the oval window (malleus - hammer, incus - anvil, stapes - stirrups)

Oval Window

The membrane-covered opening between the middle and inner ear; where amplified pressure waves from the ossicles enter the cochlea

Eustachian Tube

Connects the middle ear to the pharynx; helps maintain equal pressure on both sides of the tympanic membrane; swelling due to infection or altitude change causes pain from pressure difference

Ear Tubes (Ventilation Tubes)

Tiny cylinders (plastic or metal) surgically inserted into the tympanic membrane to allow air flow and prevent negative pressure and fluid buildup; used when Eustachian tube membranes swell during colds or ear infection

Cochlea

The spiral, fluid-filled structure of the inner ear responsible for hearing; divided into three chambers

Scala Vestibuli

Upper fluid-filled chamber of the cochlea

Scala Tympani

Lower fluid-filled chamber of the cochlea

Organ of Corti

The mechanoreceptor structure within the cochlea; contains hair cells with stereocilia; converts fluid pressure waves into nerve impulses

Hair Cells

Mechanoreceptor cells in the organ of Corti; have hair-like stereocilia on their apical surfaces; when stereocilia bend, ion channels open and action potentials are sent via the vestibulocochlear cranial nerve (CN VIII)

Stereocilia

Hair-like projections on hair cells; contact proteins that open ion channels when the array is ben

Frequency Coding in the Cochlea

Hair cells at the base of the cochlea are activated only by high frequencies; hair cells at the apex are activated only by low frequencies