DCOM 225 – Unit 2: Auditory and Vestibular Anatomy and Physiology

Comprehensive vocabulary flashcards covering anatomical foundations, outer/middle/inner ear structures, cochlear mechanics, hair cell transduction, and the vestibular balance system.

Anatomy

The study of the body's structures and their physical organization, focusing on what and where structures are.

Physiology

The study of how body structures function and work together, focusing on how something works.

Transducer

A device or anatomical mechanism that converts one form of energy into another.

Sagittal plane

An anatomical plane of reference that divides the body into left and right portions.

Midsagittal plane

An anatomical plane of reference that divides the body into equal left and right halves.

Frontal (coronal) plane

An anatomical plane of reference that divides the body into front and back portions.

Transverse (horizontal) plane

An anatomical plane of reference that divides the body into upper and lower portions.

Pinna (auricle)

Outer ear structure that captures sound waves, directs them into the external auditory canal, and aids in determining sound direction.

Tragus and concha

Specific outer ear structures that shape and direct incoming acoustic sound waves into the canal.

External auditory canal

Canal carrying sound to the tympanic membrane; it boosts specific frequencies through resonance and contains protective hairs and cerumen.

Outer $\frac{1}{3}$ of external auditory canal

The cartilaginous portion of the ear canal that contains hair follicles and ceruminous glands.

Inner $\frac{2}{3}$ of external auditory canal

The bony portion of the ear canal lined with thin, sensitive skin.

Cerumen

Yellow, orange, or brown earwax produced in the cartilaginous canal that lubricates, traps debris, and protects against bacteria and fungi.

Impedance matching

The process by which the middle ear efficiently transfers acoustic sound energy from low-impedance air into high-impedance cochlear fluid.

Tympanic membrane (TM)

A three-layered membrane that vibrates in response to acoustic sound waves and transfers mechanical movement to the ossicular chain.

Outer epithelial layer of the TM

The lateral layer of the tympanic membrane that is continuous with the skin of the external auditory canal.

Middle fibrous layer of the TM

The intermediate layer of the tympanic membrane that provides structural strength and flexibility.

Inner mucosal layer of the TM

The medial layer of the tympanic membrane that is continuous with the mucosal lining of the middle ear cavity.

Ossicles

The three tiny middle ear bones—malleus (hammer), incus (anvil), and stapes (stirrup)—that transfer mechanical vibrations to the cochlea.

Oval window

A membrane-covered cochlear opening that receives mechanical vibrations from the stapes footplate to initiate fluid pressure changes.

Tensor tympani

A middle ear muscle attached to the malleus and innervated by CN V (trigeminal nerve) that stiffens the ossicular chain.

Stapedius

A middle ear muscle attached to the stapes and innervated by CN VII (facial nerve) that is essential in the protective acoustic reflex.

Eustachian tube

A passage connecting the middle ear to the nasopharynx that equalizes air pressure, drains middle ear secretions, and opens during swallowing and yawning.

Area ratio mechanism

An impedance-matching mechanism where the larger surface area of the tympanic membrane concentrates force onto the smaller area of the stapes footplate.

Ossicular lever action

An impedance-matching mechanism where the anatomical lever arrangement of the malleus and incus provides mechanical advantage.

Tympanic membrane buckling

An impedance-matching mechanism where the curved, conical shape of the membrane helps concentrate mechanical force.

Scala vestibuli

The upper cochlear chamber filled with perilymph.

Scala media

The middle cochlear chamber filled with endolymph and housing the Organ of Corti.

Scala tympani

The lower cochlear chamber filled with perilymph.

Endolymph

The fluid found in scala media characterized by high potassium ($\text{K}^+$), low sodium ($\text{Na}^+$), and a positive electrical potential relative to perilymph.

Perilymph

The fluid filling the scala vestibuli and scala tympani, characterized by low potassium ($\text{K}^+$) and high sodium ($\text{Na}^+$).

Round window

A membrane-covered opening in the cochlea that accommodates fluid displacement and acts as a pressure-release mechanism.

Helicotrema

An anatomical opening at the cochlear apex connecting the scala vestibuli and scala tympani to allow fluid pressure communication.

Vestibule

The inner ear chamber positioned between the cochlea and semicircular canals that houses the utricle and saccule.

Basilar membrane

The structural membrane supporting the Organ of Corti that vibrates along a tonotopic gradient to encode sound frequency, intensity, and timing.

Tonotopic organization

The spatial arrangement whereby different anatomical locations within the cochlea and along the auditory pathway respond maximally to specific sound frequencies.

Cochlear base

The narrower and stiffer region of the basilar membrane that responds maximally to high-frequency sounds.

Cochlear apex

The wider and more flexible region of the basilar membrane that responds maximally to low-frequency sounds.

Organ of Corti

The sensory receptor organ of hearing situated along the basilar membrane that contains inner and outer hair cells.

Inner hair cells (IHCs)

A single row of approximately $3{,}500$ cochlear sensory cells that primarily send afferent sensory signals to the brain and lack tectorial membrane attachment.

Outer hair cells (OHCs)

Three rows of motile cochlear cells with stereocilia embedded in the tectorial membrane that amplify quiet sounds and sharpen frequency tuning.

Prestin

The motor protein that drives the electromotility and rapid length changes of outer hair cells.

Tectorial membrane

The gelatinous structure overlying the Organ of Corti in which the tallest stereocilia of outer hair cells are embedded.

Tip-links

Extracellular filamentous links connecting stereocilia that physically open or close mechanically gated ion channels when bent.

Hair cell depolarization

Electrical excitation occurring when stereocilia bend toward the tallest stereocilia, opening ion channels for $\text{K}^+$ entry and increasing neurotransmitter release.

Hair cell hyperpolarization

Electrical inhibition occurring when stereocilia bend away from the tallest stereocilia, closing ion channels, reducing $\text{K}^+$ entry, and decreasing neurotransmitter release.

Traveling wave

A wave of fluid displacement moving along the basilar membrane from the base toward the apex, peaking at the site tuned to the sound frequency.

Cranial nerve VIII

The vestibulocochlear nerve, consisting of a cochlear branch for hearing and a vestibular branch for balance and head-motion signals.

Proprioception

A component of balance that provides sensory information from muscles, joints, and skin regarding body movement and spatial position.

Vertigo

A false sensory perception of spinning or movement of oneself or the surroundings in the absence of actual physical motion.

Semicircular canals

Three fluid-filled bony canals (anterior, posterior, and lateral) that detect rotational head acceleration through hair cells in their ampullae.

Utricle

An otolith organ that detects horizontal linear acceleration, such as moving forward in a car.

Saccule

An otolith organ that detects vertical linear acceleration, such as riding an elevator.

Otoconia

Calcium carbonate crystals located within the otolith organs (utricle and saccule) that provide inertial mass to detect gravity and linear acceleration.