Cochlea, Inner Ear, and Vestibular System Concepts

A set of vocabulary flashcards summarizing key concepts from the cochlea, inner ear, vestibular system, and associated pathways.

What are the three scalae of the cochlea?

The Scala Vestibuli, scala media, and scala tympani

Scala Vestibuli

The upper chamber of the cochlea that contains perilymph.

Scala Media

The middle chamber of the cochlea that contains endolymph and houses the Organ of Corti.

Scala Tympani

The lower chamber of the cochlea also containing perilymph and ending at the round window.

Endolymph

The fluid found in the scala media of the cochlea.

Perilymph

The fluid in the scala tympani

Basilar Membrane

Becomes wider and more flexible toward the apex, coding for low frequencies

What is the strong positive charge that’s drives K+ into hair cells?

Endocochlear potential

What does the tectorial membrane make direct contact with?

Outer hair cells

What hair cell sends 95% of auditory information to the brain?

Inner ear cells

Helicotrema

The apex of the cochlea that connects the scala vestibuli and scala tympani.

Spiral Ganglion Cells

Nerve cells that form the cochlear or auditory nerve.

Frequency encoding on Basilar Membrane: Base

HIGH frequency sound (narrow, stiff)

Frequency encoding on Basilar Membrane: Apex

LOW frequency sounds (wide, flexible)

tonotopic organization

The arrangement of auditory neurons in the cochlea that corresponds to different frequencies of sound, where specific areas are tuned to specific frequencies, creating a map of sound frequency along the membrane.

How are traveling wave peaks happen?

based on the point of most resistance

Scala Vestibuli (superior-chamber)

Contains perilymph, begins at oval window, separated from scala media by Reisner’s membrane

Scala Media (middle/cochlear duct chamber)

contains endolymph, houses organ of Corti, maintained by stria vascularis

Scala Tympani (inferior chamber)

contains perilymph, ends at round window, round widow ensures sound energy doesn’t reflect back

Hair cell comparison chart

what hair cells have motor function?

Outer hair cells have motor function.

Hiar cell Transduction Process

Sound>BM Movement> Stereocilia bend> Mechanotransduction channels open> K+ enters hair cell (driven by Endocochlear potential)> depolarization occurs> Neurotransmitter (glutamate) release>auditory nerve fired

What is depolarization caused by?

K+ Influx

Stria Vascularis

Contains capillary loops and blood vessels, vascular tissue with epithelial cells, produces endolymph, creates endococlear potential (+80 mV)

Tectorial Membrane

Semi-transparent structure over hair cells, indented by OHC stereocilia, purely mechanical role

extra important supporting cells

Deiter’s cells, Hensen’s cells, Claudius cells, Pillar cells (NOT epley’s cells)

Inner hair cell depolarization occurs due to an influx of what?

K+

Structure responsible for maintaining endolymphatic volume

stria vascularis; a specialized tissue in the cochlea that regulates the production and absorption of endolymph, maintaining ionic balance.

frequency tuning in the cochlea results from?

Basilar membrane mechanical properties

Outer hair cells?

They sharpen frequency tuning

Auditory nerve fibers for high frequencies are located?

along the base of the cochlea

structure ensuring sound energy doesn’t reflect back?

round window

What is the osseous?

Bone

Afferent

toward the brain (sensory input)

Efferent

away from the brain (motor output)

tonotopic organization

frequency mapping preserved throughout system

The semicircular canals detect what acceleration?

angular/rotational

The otolith organs detect what acceleration and head position/tilt?

linear

The sensory structure in the otolith organs is the?

macula

The gelatinous structure containing otoconia is called?

the otholithic membrane.

Endolymph movement bends the hair cells?

Stereocillia/kinocillium

What does VOR do?

stabilizes vision/gaze during head movement

What does the push-pull dynamic refer to?

one canal being excited while the paired canal is inhibited

The horizontal canals are activated most by?

turning the head to the left or right (yaw)

How is the saccule oriented?

in the vertical/sagittal plane

How is the utricle oriented?

on the horizontal plane

The Five Mechanoreceptors (per ear): Utricle

horizontal linear acceleration

The Five Mechanoreceptors (per ear): Saccule

vertical linear acceleration

The Five Mechanoreceptors (per ): Superior semicircular canal

pitch (nodding "yes")

The Five Mechanoreceptors (per ear):Posterior semicircular canal

roll (tilting side-to-side)

The Five Mechanoreceptors (per ): Horizontal semicircular canal

yaw (shaking "no")

Utricle details

Larger of two membranous sacs, Elliptical, lies most laterally, Hair cells oriented with kinocilium TOWARD striola, Responds best to side-to-side/horizontal movement

Saccule details

Smaller membranous sac, Primary sensor for vertical movement (jumping, elevator), Oriented in vertical plane

Macula Structure details (both organs)

1. Otoconia - calcium carbonate crystals (top layer)

2. Otolithic membrane - gelatinous layer

3. Stereocilia - hair bundles

4. Kinocilium - tallest cilium

5. Type II Hair Cells - sensory receptors

Otoconia facts

Composed of calcium carbonate crystals

● HIGH density (increase specific gravity above endolymph)

● Provide inertia to detect linear acceleration

● When they break loose → cause BPPV (Benign Paroxysmal Positional Vertigo)

● Do NOT cause Meniere's disease

Three canals per ear: Superior

Superior (anterior) - pitch movements

Three canals per ear: Posterior

Posterior - roll movements

Three canals per ear: Horizontal

Horizontal (lateral) - yaw movements

Key canal pairings:

● Left horizontal ↔ Right horizontal

● Right superior ↔ Left posterior (contralateral)

● Left superior ↔ Right posterior (contralateral)

Each ampulla contains what?

crista

Why is endolymph flow opposite of head movement?

due to inertia

what does exciting one canal do to its paired canal?

inhibitsthe activity of the paired canal.

Vestibular hair cell properties

● Have continuous activity with directional sensitivity

● Always firing—just change firing rate

● Found in cristae (canals) and maculae (otoliths)

● NOT located in Organ of Corti

Directional responses: toward kinocilium

Toward kinocilium → Depolarizes → Increases firing rate

Directional response: Away from kinocilium

Away from kinocilium → Hyperpolarizes → Decreases firing rate

Vestibular activation sequence

1. Head rotates

2. Endolymph lags behind (inertia)

3. Cupula deflects

4. Hair cells bend

5. Depolarization occurs

6. Signal travels through vestibular nerve (CN VIII)

In unilateral vestibular loss, the brain interprets “resting asymmetry” as?

constant rotation/spinning

In BPPV what breaks loose and falls into the semicircular canal?

Otoconia (ear crystals)

Cupula deflects because of movement of

endolymph in the semicircular canals.

Reflex stabilizing body during sudden shifts

called the vestibulo-ocular reflex (VOR). It helps maintain stable vision while the head moves.

Utricle responds best to?

side-to-side movements

Hair cells within the ampulla are oriented towards?

the kinocilium, the tallest stereocilia.

The superior canal detects?

pitching/nodding yes

Three primary functions of the vestibular function

1. Image stabilization (VOR)

2. Balance control (VSR)

3. Spatial orientation

Thinf the vestibular function does not do

provide hearing, aid in sound localization, drain mucus from the middle ear

What three systems are required to balance information sources?

1. Vestibular system

2. Visual system

3. Proprioception (joint/muscle sense)

correction response

automatic responses to unexpected changes in the center of gravity

Other types of balance responses

maintenance responses, stabilization response, preservation response

What is the purpose of the vestibulo-oculomotor reflex

keeps visual target in view when the head moves by stabilizing the eyes during head movement.

Vestibulo-oculomotor reflex (VOR) Neural pathways

Input: CN VIII (vestibular nerve)

Processing: Vestibular nuclei

Output: CN III, IV, VI (oculomotor, trochlear, abducens)

Result: Eye muscles contract/relax appropriately

Nystagmus (VOR)

Eye movement response to vestibular stimulation, seen during acceleration and deceleration, NOT seen during constant velocity

Medial Vestibulospinal Tract

Controls head and neck movements only, NOT full body (common misconception!)

Lateral Vestibulospinal Tract

Controls head and neck movements only, NOT full body (common misconception!)

Lateral Vestibulospinal Tract

Controls trunk and limb movements, Maintains posture and balance

ECOLI-MA

E = Eighth nerve (CN VIII/cochlear nerve)

C = Cochlear nucleus

O = Olivary complex (superior)

L = Lateral lemniscus

I = Inferior colliculus

M = Medial geniculate body (MGB)

A = Auditory cortex

Cochlear Nucleus (medulla/pons)

First central processing station, all auditory fibers synapse here, Wave III of ABR

Superior Olivary Complex

Critical for sound localization

ITD (Interaural Time Differences) = horizontal/azimuth sound clues ILD (Interaural Level Differences) = intensity/level sound clues Initiates acoustic reflex

ITD (Interaural Time Differences)

horizontal/azimuth sound clues

ILD (Interaural Level Differences)

intensity/level sound clues Initiates acoustic reflex

Lateral Lemniscus

Pathway connecting lower to upper brainstem, projects from cochlear nucleus to inferior colliculus

Inferior Colliculus (midbrain)

Integrates multisensory attention to sound

Contributes to reflexive orienting to sound

Nearly all auditory fibers synapse here

Medial Geniculate Body (MGB - thalamus)

Thalamic relay station

Lesion affects auditory attention and relay to cortex

Sends projections to auditory cortex

Auditory

Brodmann areas 41 & 42

High-level interpretation

Pitch discrimination, complex sound processing

Lesion does NOT cause complete deafness (bilateral input)

Tonotopy Preservation

Maintained by basilar membrane organization

Preserved through cochlear nucleus, inferior colliculus, MGB, auditory cortex

NOT preserved in: utricle, vestibular structures

Binaural Integration

Corpus callosum connects left and right hemispheres

Enables integration of information from both ears

Why cortical lesions don't cause complete deafness in one ear

Structure sending projections through lateral lemniscus

Cochlear nucleus

Structure integrating multisensory attention to sound

Medial geniculate body (also accept inferior colliculus)

Wave III of ABR associated with

Cochlear nucleus

Lesion in MGB would most affect

Auditory attention and relay to cortex

Everything that contains perilymph

Scala tympani, scala vestibuli