Lecture 13 C: Special Senses - Hearing & Equilibrium

Vocabulary practice flashcards covering the anatomical regions of the external, middle, and inner ear, as well as the structures and physiological mechanisms responsible for hearing and static and dynamic equilibrium.

Auditory tube (Eustachian tube)

A passage connecting the middle ear to the nasopharynx (throat) that equalizes pressure in the middle ear and helps drain fluids; it is shorter and more horizontal in children than in adults.

Auricle (Pinna)

The outer, visible portion of the external ear composed of elastic cartilage that funnels sound waves into the ear canal.

Ceruminous glands

Specialized glands in the external ear canal that produce earwax for protection.

External acoustic meatus

The canal of the external ear that directs sound waves from the auricle to the tympanic membrane.

Tympanic membrane

Also called the eardrum; a thin membrane that vibrates in response to sound waves and marks the boundary between the external ear and the middle ear.

Auditory ossicles

The three tiny bones of the middle ear—malleus, incus, and stapes—that amplify sound waves and transfer vibrations from the tympanic membrane to the oval window.

Malleus

The most superficial auditory ossicle that is attached to the tympanic membrane and transfers vibrations to the incus.

Incus

The middle auditory ossicle that transmits vibrations between the malleus and the stapes.

Stapes

The deepest auditory ossicle that fits into the oval window to generate pressure waves in the inner ear fluid.

Oval window

The membrane-covered opening between the middle ear and inner ear that is vibrated by the stapes to create pressure waves in the perilymph of the scala vestibuli.

Round window

The membrane-covered opening at the end of the cochlea through which remaining pressure waves exit the inner ear from the scala tympani.

Bony labyrinth

Chambers within the petrous part of the temporal bone lined with bone and filled with perilymph, comprising the cochlea, vestibule, and semicircular canals.

Membranous labyrinth

The membrane-lined, fluid-filled sacs and ducts situated inside the bony labyrinth that contain endolymph and sensory receptor organs.

Perilymph

The fluid contained within the bony labyrinth surrounding the membranous labyrinth.

Endolymph

The fluid found inside the membranous labyrinth where the sensory receptors for hearing and equilibrium are directly located.

Static equilibrium

The perception of the orientation of the head relative to gravity (determining up versus down), which is sensed within the vestibule.

Dynamic equilibrium

The perception of rotational movement or tilting of the head in three-dimensional space, which is sensed within the semicircular canals.

Vestibule

The central part of the bony labyrinth containing the organs responsible for sensing static equilibrium.

Macula

The sensory receptor structure for static equilibrium located in the vestibule, composed of hair cells, supporting cells, and an otolithic membrane.

Otoliths

Microscopic calcium carbonate stones embedded in the gelatinous layer of the otolithic membrane that provide mass to bend hair cell stereocilia during head tilts.

Otolithic membrane

A gelatinous layer embedded with otoliths in which the stereocilia of hair cells in the macula are inserted.

Stereocilia

Specialized microvilli on hair cells in the inner ear that bend in response to fluid or membrane movement, triggering a nerve impulse.

Semicircular canals

Three bony tubes oriented in three planes of space ($X$, $Y$, and $Z$) that house receptors for dynamic equilibrium.

Ampulla

The expanded swelling at the base of each semicircular canal that contains the crista ampullaris.

Crista ampullaris

The receptor for dynamic equilibrium located in the ampulla of each semicircular canal, consisting of hair cells covered by a cupula.

Cupula

A gel-like structure covering the hair cells of the crista ampullaris that is displaced by the inertia of moving endolymph when the head rotates.

Cochlea

The snail-shaped region of the inner ear containing sensory receptors dedicated exclusively to hearing.

Spiral organ (Organ of Corti)

The specialized sensory structure for hearing within the cochlear duct where fluid pressure waves are transformed into nerve impulses.

Basilar membrane

The membrane supporting the spiral organ that moves in response to pressure waves in the cochlear duct, stimulating hair cells against the tectorial membrane.

Tectorial membrane

A stationary gelatinous membrane in the spiral organ that overlies and physically bends the stereocilia of inner and outer hair cells.

Vestibulocochlear nerve (CN VIII)

The cranial nerve whose vestibular branch carries equilibrium signals and whose cochlear branch transmits auditory signals to the brain.