Hearing and Equilibrium: The Anatomy and Physiology of the Ear

Comprehensive vocabulary flashcards covering the anatomical structures, auditory pathways, and equilibrium mechanisms of the external, middle, and inner ear.

Sound

Vibrations in the air that beat against the eardrum, push a series of tiny bones, move internal fluid against a membrane, and trigger hair cells that stimulate neurons to transmit action potentials to the brain.

Frequency

The number of sound waves that pass a certain point at a given time, which determines the perceived pitch of a sound.

Amplitude

The difference between the high and low pressures created in the air by a sound wave, which dictates how loud a sound registers.

Pinna (Auricle)

The visible external part of the ear made of skin-covered elastic cartilage whose primary role is to catch sound waves and funnel them inward.

External Acoustic Meatus

The auditory canal through which captured sound waves are directed inward toward the middle and inner ear.

Tympanic Membrane

An ultra-sensitive, translucent, slightly cone-shaped sheet of connective tissue (the eardrum) separating the external and middle ear that vibrates in response to sound waves.

Tympanic Cavity

The middle ear compartment that serves as a relay station to amplify sound vibrations so they can move fluid within the inner ear.

Auditory Ossicles

A trio of the smallest bones in the human body—the malleus, incus, and stapes—that amplify and transmit mechanical vibrations from the eardrum to the inner ear.

Malleus

The auditory ossicle commonly known as the hammer, which connects directly to the inner surface of the tympanic membrane and articulates with the incus.

Incus

The intermediate auditory ossicle commonly called the anvil, positioned between and connecting the malleus to the stapes.

Stapes

The auditory ossicle commonly called the stirrup, which attaches to the incus and transfers vibrations into the superior oval window.

Superior Oval Window

The membrane boundary on the inner ear that receives vibrations from the stapes to set internal fluid into motion.

Labyrinth

The intricate, maze-like inner ear structure deeply embedded within the skull, responsible for both sound transduction and maintaining equilibrium.

Bony Labyrinth

The outer, fluid-filled network of passageways within the temporal bone that encases the membranous labyrinth.

Membranous Labyrinth

The continuous internal system of communicating sacs and ducts positioned inside the bony labyrinth that shares its general contour.

Cochlea

The snail-shell-shaped structure of the inner ear comprising three internal chambers separated by sensitive membranes that houses the sensory apparatus for hearing.

Basilar Membrane

A stiff band of tissue spanning the cochlea containing more than $20{,}000$ fibers that vibrate differentially according to pitch, with short, stiff base fibers responding to high frequencies and long, loose apex fibers responding to low frequencies.

Organ of Corti

The receptor organ resting on top of the basilar membrane that contains nerve cells and sensory hair cells that transduce mechanical fluid movement into electrical impulses.

Mechanically Gated Sodium Channels

Ion channels on cochlear hair cells that open when triggered by physical movement, allowing sodium influx to generate graded potentials and eventual action potentials.

Vestibular Apparatus

The inner ear system composed of semicircular canals, the utricle, and the saccule that utilizes fluid and sensory hair cells to monitor head movement and maintain equilibrium.

Semicircular Canals

Three fluid-filled loops situated in the sagittal, frontal, and transverse anatomical planes that detect rotational head movements including nodding, tilting, and shaking side-to-side.

Utricle and Saccule

Sac-like structures located at the base of the semicircular canals filled with sensory hair cells that track fluid movement to inform the brain of head acceleration.

Sensory Conflict

A mismatch between vestibular fluid signals and input from visual or joint receptors regarding physical movement, which causes the sensation of motion sickness.