Inner Ear – Anatomy, Physiology & Disorders (Audiology Ch. 10)

Vocabulary flashcards summarizing key anatomy, physiology, and pathology terms related to the inner ear from Audiology Chapter 10.

Inner Ear (Labyrinth)

Complex system of bony and membranous chambers that converts mechanical energy into electrochemical nerve impulses and provides balance information.

Vestibular Portion

Section of the inner ear that houses the organs of equilibrium.

Cochlear Portion

Section of the inner ear that contains the organ of hearing.

Utricle

Membranous sac in the vestibule that responds to horizontal linear acceleration.

Saccule

Membranous sac in the vestibule that responds to vertical acceleration.

Semicircular Canals

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

Ampulla

Enlarged end of each semicircular canal where sensory cristae are located.

Endolymph

Inner-ear fluid high in potassium and low in sodium; positively charged.

Perilymph

Inner-ear fluid high in sodium and low in potassium; similar to cerebrospinal fluid; negatively charged.

Ductus Reuniens

Narrow pathway connecting cochlear endolymph (scala media) to vestibular endolymph.

Cochlea

Snail-shaped bony shell (~1 cm wide, 5 mm long, 2.5 turns) that houses the auditory receptor organ.

Scala Vestibuli

Upper perilymph-filled chamber of the cochlea beginning at the oval window.

Scala Media (Cochlear Duct)

Middle endolymph-filled chamber of the cochlea containing the organ of Corti.

Scala Tympani

Lower perilymph-filled chamber of the cochlea beginning at the round window.

Helicotrema

Apex opening where scala vestibuli and scala tympani communicate.

Reissner’s Membrane

Thin membrane separating scala media from scala vestibuli.

Basilar Membrane

Structure supporting the organ of Corti; varies in width and is tonotopically organized.

Organ of Corti

End organ of hearing situated on the basilar membrane containing sensory hair cells.

Tectorial Membrane

Gelatinous flap that overlies and stimulates stereocilia of outer hair cells.

Outer Hair Cells (OHC)

3–5 rows (~12,000–15,000) that enhance frequency discrimination and are highly vulnerable.

Inner Hair Cells (IHC)

Single row (~3,000) that send the majority of auditory information to the brain.

Stereocilia

Hair-like projections atop hair cells that shear during basilar-membrane motion, triggering transduction.

Spiral Ligament

Lateral wall support structure for the scala media.

Stria Vascularis

Vascular epithelium that produces endolymph and supplies blood, oxygen, and nutrients to the cochlea.

Modiolus

Central bony core of the cochlea where blood vessels and nerve fibers enter.

Tonotopic Organization

Systematic arrangement where high frequencies stimulate the basal cochlea and low frequencies the apical end.

Békésy’s Traveling Wave Theory

Concept that stapes motion creates a fluid wave causing place-specific maximal displacement on the basilar membrane.

Hair-Cell Transduction

Process where stereocilia deflection opens ion channels, producing electrical signals that release neurotransmitters.

Action Potential (AP)

Change in electrical potential in auditory neurons when stimulated by hair-cell activity.

Afferent Neurons

≈30,000 sensory fibers carrying impulses from cochlea to the central auditory system.

Efferent Neurons

≈1,800 fibers projecting from superior olivary complex to hair cells, modulating cochlear responses.

Spiral Ganglion

Collection of afferent neuron cell bodies within the modiolus.

Otoacoustic Emissions (OAEs)

Sounds generated by the cochlea, useful for screening and site-of-lesion testing.

Spontaneous OAEs (SOAEs)

Emissions occurring without external stimuli; present in 40–60 % of normal-hearing ears.

Transient-Evoked OAEs (TEOAEs)

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

Distortion-Product OAEs (DPOAEs)

Emissions produced by two simultaneous tones; useful for high-frequency monitoring of cochlear health.

Vertigo

Sensation of spinning or whirling often due to vestibular dysfunction.

Nystagmus

Rapid, involuntary eye movements associated with vestibular disorders.

Sensorineural Hearing Loss (SNHL)

Hearing loss stemming from inner-ear (sensory) or auditory-nerve (neural) damage.

Congenital/Prenatal Hearing Loss

Loss present at birth due to genetic factors, maternal infections, or inner-ear malformations.

Perinatal Hearing Loss

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

Acquired/Postnatal Hearing Loss

Loss developing after birth from diseases, noise, ototoxicity, aging, etc.

Ototoxicity

Hearing damage caused by drugs or chemicals toxic to the cochlea or vestibular nerve.

Ototoxic Antibiotics

Agents such as gentamycin, tobramycin, and amikacin that can harm hair cells, especially at high frequencies.

Noise-Induced Hearing Loss (NIHL)

SNHL from exposure to loud sounds, leading to temporary (TTS) or permanent (PTS) threshold shifts.

Presbycusis

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

Ménière’s Disease

Inner-ear disorder marked by endolymphatic hydrops causing episodic vertigo, tinnitus, and fluctuating low-frequency SNHL.

Sudden Idiopathic SNHL (SISNHL)

Rapid unilateral hearing loss ≥30 dB across 3 octaves within 72 h; medical emergency.

Autoimmune Inner-Ear Disease (AIED)

Bilateral, fluctuating, progressive SNHL caused by immune attack on inner-ear tissues.

Semicircular Canal Dehiscence Syndrome (SCDS)

Balance disorder from thinning bone over semicircular canals creating a ‘third window’; causes vertigo and disequilibrium.

Equilibrium (Balance)

Function relying on integrated visual, proprioceptive, and vestibular inputs to maintain body orientation.

Linear Acceleration

Straight-line movement sensed by the utricle (horizontal) and saccule (vertical).

Angular Acceleration

Rotational movement detected by semicircular canals.

Temporary Threshold Shift (TTS)

Short-term hearing decrease that recovers after noise exposure.

Permanent Threshold Shift (PTS)

Irreversible hearing loss following damaging noise exposure.

Endolymphatic Hydrops

Excess accumulation of endolymph associated with Ménière’s disease.

Phonemic Regression

Disproportionate decline in speech understanding relative to pure-tone thresholds, common in presbycusis.

Development of Inner Ear

Begins week 3 of gestation; adult size by 6 months with full formation by week 25.

Crista Ampullaris

Sensory epithelium inside each ampulla that detects angular acceleration.

Helicotrema Function

Allows perilymph communication between scala vestibuli and scala tympani at cochlear apex.

Stria Vascularis Role

Maintains ionic composition of endolymph and endocochlear potential necessary for hair-cell function.

Outer Hair Cell Motility

Ability of OHCs to change length, sharpening basilar-membrane vibration and amplifying sound.

Endocochlear Potential

Positive electrical potential (≈+80 mV) within scala media essential for hair-cell transduction.

Noise Notch

Characteristic dip around 3–6 kHz on an audiogram indicative of NIHL.

Stereocilia Shearing

Twisting movement between tectorial and basilar membranes that initiates hair-cell depolarization.