Ear Anatomy and Function

Overview

This lecture covers the anatomy and functions of the ear in hearing and equilibrium, detailing how sound is detected and how balance is maintained.

The ear is divided into external, middle, and internal parts.
The external ear includes the auricle (pinna) and external acoustic meatus, funneling sound to the middle ear.
The middle ear contains the tympanic membrane (eardrum) and auditory ossicles (malleus, incus, stapes).
The auditory tube (Eustachian tube) connects the middle ear to the nasal cavity to equalize pressure.
Sound waves cause the tympanic membrane to vibrate, moving the auditory ossicles and transmitting vibrations to the oval window of the inner ear.
The stapes vibrates against the oval window, sending vibrations into the fluid-filled cochlea.

Sound waves are vibrations in air, perceived as changes in air pressure.
Amplitude of sound waves determines loudness; frequency determines pitch.
Vibrations in the cochlea stimulate the basilar membrane, affecting the spiral organ (organ of Corti).
Inner hair cells with stereocilia, embedded in the tectorial membrane, act as sensory receptors.
Movement of the basilar membrane bends stereocilia, opening cation channels, causing depolarization and sending signals to the brain via the vestibulocochlear nerve.
Outer hair cells adjust the sensitivity of hearing.
Damage to hair cells can cause tinnitus (ringing in the ears).

Balance is detected in the semicircular canals of the inner ear, filled with endolymph fluid.
Maculae detect head tilt and position relative to gravity; contain hair cells embedded in the otolithic membrane with calcium carbonate crystals (otoliths).
Tilting the head shifts the otolithic membrane, bending stereocilia and activating hair cells.
Crista ampullaris detects rotational movement; endolymph movement bends the cupula, stimulating hair cells.
Visual cues assist balance; disturbances in inner ear can cause vertigo.

Auricle (Pinna) — external visible part of the ear that funnels sound.
Tympanic Membrane — eardrum; vibrates in response to sound.
Auditory Ossicles — three small bones (malleus, incus, stapes) transmitting vibrations.
Oval Window — membrane between middle and inner ear.
Cochlea — spiral-shaped, fluid-filled structure for hearing.
Semicircular Canals — structures for balance and equilibrium.
Endolymph — fluid inside cochlea and semicircular canals.
Hair Cells — sensory receptors with stereocilia for hearing and balance.
Maculae — structures detecting head tilt.
Crista Ampullaris — detects rotational movements in semicircular canals.
Otolithic Membrane — gelatinous membrane with otoliths for sensing gravity.
Tinnitus — ringing in the ears, often due to hair cell damage.