Chapter 10 – The Inner Ear: Key Vocabulary

A comprehensive set of vocabulary flashcards covering anatomy, physiology, and disorders of the inner ear as presented in Chapter 10.

Inner Ear (Labyrinth)

Complex system of bony and membranous chambers that converts mechanical sound energy to neural signals and provides balance information.

Bony Labyrinth

Rigid, outer bony casing of the inner ear that houses the membranous labyrinth; contains perilymph.

Membranous Labyrinth

Soft-tissue system suspended within the bony labyrinth; filled with endolymph.

Vestibular Portion

Balance division of the inner ear containing the utricle, saccule, and semicircular canals.

Cochlear Portion

Auditory division of the inner ear; spiral-shaped organ of hearing.

Endolymph

Inner-ear fluid high in potassium and low in sodium that fills the scala media, utricle, saccule, and semicircular canals.

Perilymph

Fluid high in sodium and low in potassium that fills the scala vestibuli and scala tympani and surrounds the membranous labyrinth.

Utricle

Membranous sac in the vestibule that detects horizontal linear acceleration.

Saccule

Membranous sac in the vestibule that detects vertical acceleration.

Semicircular Canals

Three perpendicular fluid-filled canals (superior, lateral, posterior) that detect angular head movements.

Superior (Anterior) Canal

Semicircular canal sensitive to pitching movement (head tilting toward shoulders).

Lateral (Horizontal) Canal

Semicircular canal sensitive to yaw movement (shaking head “no”).

Posterior Canal

Semicircular canal sensitive to roll movement (nodding head “yes”).

Ampulla

Enlarged end of each semicircular canal that contains the sensory cristae.

Crista Ampullaris

Sensory organ within each ampulla that responds to angular acceleration.

Equilibrium

Ability to maintain balance through combined visual, proprioceptive, and vestibular input.

Vertigo

Illusion of spinning or whirling often caused by vestibular dysfunction.

Nystagmus

Reflexive, rapid eye movement that accompanies vestibular stimulation or disorder.

Cochlea

Snail-shaped bony structure (≈5 mm long, 2.5 turns) responsible for hearing.

Scala Vestibuli

Upper cochlear chamber beginning at the oval window; contains perilymph.

Scala Media (Cochlear Duct)

Middle cochlear chamber filled with endolymph; houses the Organ of Corti.

Scala Tympani

Lower cochlear chamber beginning at the round window; contains perilymph.

Helicotrema

Apex opening where scala vestibuli and scala tympani communicate.

Reissner’s Membrane

Thin partition separating the scala vestibuli from the scala media.

Basilar Membrane

Fibrous membrane supporting the Organ of Corti; tonotopically organized—high frequencies at base, low at apex.

Organ of Corti

End organ of hearing sitting on the basilar membrane; contains sensory hair cells.

Tectorial Membrane

Gelatinous membrane overlying hair-cell stereocilia within the Organ of Corti.

Stria Vascularis

Vascular tissue lining the scala media that produces endolymph and supplies nutrients.

Spiral Ligament

Connective-tissue band supporting the lateral wall of the scala media.

Modiolus

Central bony core of the cochlea through which nerve fibers and blood vessels travel.

Outer Hair Cells (OHC)

3-5 rows (~12,000–15,000) that amplify and sharpen the basilar-membrane response; highly vulnerable to damage.

Inner Hair Cells (IHC)

Single row (~3,000) that convert cochlear motion into neural signals; primary sensory cells for hearing.

Stereocilia

Hair-like projections atop each hair cell that bend (shear) in response to fluid waves.

Tonotopic Organization

Spatial arrangement where specific frequencies activate particular places along the basilar membrane and auditory pathway.

Afferent Neurons

~30,000 sensory fibers that carry signals from the cochlea to the brain.

Efferent Neurons

~1,800 fibers traveling from the superior olivary complex to the cochlea, modulating hair-cell activity.

Action Potential

Electrical change generated in auditory neurons when hair cells stimulate them; size grows with stimulus intensity.

Békésy’s Traveling Wave Theory

Concept that each sound causes a wave along the basilar membrane with peak displacement at a place corresponding to frequency.

Otoacoustic Emissions (OAEs)

Sounds generated by the cochlea, recordable in the ear canal; indicate OHC function.

Spontaneous OAEs (SOAEs)

Naturally occurring emissions present in 40–60 % of normal ears, more in females and right ears.

Transient-Evoked OAEs (TEOAEs)

Emissions elicited by brief stimuli; absent when hearing thresholds exceed ~30 dB HL.

Distortion-Product OAEs (DPOAEs)

Emissions generated by two simultaneous tones; useful for detecting high-frequency cochlear damage.

Sensorineural Hearing Loss (SNHL)

Hearing loss arising from inner-ear (sensory) and/or auditory-nerve (neural) damage.

Prenatal (Congenital) Hearing Loss

Loss originating before birth due to genetics, maternal infection, or developmental malformation.

Perinatal Hearing Loss

Loss occurring during birth, e.g., anoxia, CMV exposure, or head trauma.

Postnatal (Acquired) Hearing Loss

Loss developing after birth from disease, noise, ototoxic drugs, aging, etc.

Ototoxicity

Inner-ear damage caused by drugs or chemicals (e.g., aminoglycoside antibiotics, chemotherapy agents).

Noise-Induced Hearing Loss (NIHL)

SNHL resulting from damaging sound exposure; shows temporary (TTS) or permanent (PTS) threshold shifts.

Temporary Threshold Shift (TTS)

Short-term, mostly reversible hearing reduction after loud sound exposure.

Permanent Threshold Shift (PTS)

Irreversible hearing loss following damaging noise exposure.

Presbycusis

Age-related progressive SNHL often accompanied by difficulty understanding speech (phonemic regression).

Ménière’s Disease

Inner-ear disorder marked by fluctuating low-frequency hearing loss, vertigo, tinnitus, and aural fullness due to endolymphatic hydrops.

Sudden Idiopathic SNHL (SISNHL)

Rapid unilateral hearing loss of ≥30 dB across three octaves within 72 h; medical emergency.

Autoimmune Inner-Ear Disease (AIED)

Progressive, bilateral SNHL caused by immune attack on inner-ear tissues; may include tinnitus and vertigo.

Semicircular Canal Dehiscence Syndrome (SCDS)

Balance disorder due to thinning of bone over a semicircular canal, creating a ‘third window’ and causing vertigo and disequilibrium.

Labyrinthitis

Inflammation/infection of the inner-ear labyrinth that can produce hearing loss and/or vertigo.

Endolymphatic Hydrops

Excessive buildup of endolymph associated with Ménière’s disease.

Ductus Reuniens

Narrow channel connecting endolymph of the cochlear duct to the vestibular system.

Development of Inner Ear

Begins in 3rd gestational week; cochlear turns form by week 10; adult size reached by 25th week.

Proprioception

Somatosensory feedback from muscles and joints that contributes to balance.