The Ear’s Role in The Ear’s Role in Balance and Balance and EquilibriumEquilibrium

The EarThe Ear

Houses two sensesHouses two senses

1.1. Hearing Hearing

2.2. Equilibrium (balance)Equilibrium (balance) Receptors are mechanoreceptorsReceptors are mechanoreceptors Different organs house receptors Different organs house receptors

for each sensefor each sense

Anatomy of the EarAnatomy of the Ear

The ear is divided into three areasThe ear is divided into three areas1.1. External earExternal ear

2.2. Middle earMiddle ear

3.3. Inner earInner ear

The External EarThe External Ear Involved in hearing onlyInvolved in hearing only Structures of the external earStructures of the external ear

1.1. Pinna (auricle)Pinna (auricle)

2.2. External auditory canalExternal auditory canal

The Middle Ear The Middle Ear Air-filled cavity within the temporal boneAir-filled cavity within the temporal bone Only involved in the sense of hearingOnly involved in the sense of hearing Two tubes are associated with the inner earTwo tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic The opening from the auditory canal is covered by the tympanic membranemembrane

The auditory tube connecting the middle ear with the throatThe auditory tube connecting the middle ear with the throat Allows for equalizing pressure during yawning or swallowingAllows for equalizing pressure during yawning or swallowing This tube is otherwise collapsedThis tube is otherwise collapsed

Three bones span the cavityThree bones span the cavity1.1. Malleus (hammer)Malleus (hammer)2.2. Incus (anvil)Incus (anvil)3.3. Stapes (stirrup)Stapes (stirrup)

Vibrations from eardrum move the malleusVibrations from eardrum move the malleus These bones transfer sound to the inner earThese bones transfer sound to the inner ear

The Inner Ear or Bony The Inner Ear or Bony

LabyrinthLabyrinth

Includes sense organs Includes sense organs for hearing and balancefor hearing and balance

Filled with perilymphFilled with perilymph A maze of bony A maze of bony

chambers within the chambers within the temporal bonetemporal bone

Semicircular canals – organ for dynamic equilibrium

Cochlea – organ for hearing

Vestibule – organ for static equilibrium

Organs of the Inner Ear

Organs of EquilibriumOrgans of Equilibrium

Receptor cells are in two structuresReceptor cells are in two structures1.1. Vestibule (static)Vestibule (static)

2.2. Semicircular canals (dynamic)Semicircular canals (dynamic)

Equilibrium has two functional partsEquilibrium has two functional parts1.1. Static equilibriumStatic equilibrium

2.2. Dynamic equilibriumDynamic equilibrium

Static EquilibriumStatic Equilibriumreceptors are in the vestibulereceptors are in the vestibule

Maculae – receptors on the Maculae – receptors on the membranes of the membranes of the vestibulevestibule

Report on the position of Report on the position of the headthe head

Send information via the Send information via the vestibular nervevestibular nerve

Dynamic EquilibriumDynamic Equilibriumreceptors are in the semicircular receptors are in the semicircular

canalscanalsCrista ampullaris – receptors in the Crista ampullaris – receptors in the

semicircular canalssemicircular canals Tuft of hair cellsTuft of hair cells Cupula (gelatinous cap) covers the Cupula (gelatinous cap) covers the

hair cellshair cells

Action of angular head movementsAction of angular head movements The cupula stimulates the hair cellsThe cupula stimulates the hair cells An impulse is sent via the vestibular An impulse is sent via the vestibular

nerve to the cerebellumnerve to the cerebellum

Review of the balance and equilibrium organs in the inner

earI. STATIC EQUILIBRIUM – position of the

head in space The organ is the vestibule The receptor inside the vestibule is

the maculae

II. DYNAMIC EQUILIBRIUM – action of action of angular head movementsangular head movements

The organ is the semicircular canals

The receptor inside the semicircular canals is the crista ampullaris

Symptoms of Meniere’s Symptoms of Meniere’s DiseaseDisease

The symptoms of Ménière’s disease are The symptoms of Ménière’s disease are episodic rotational vertigo (attacks of a episodic rotational vertigo (attacks of a spinning sensation)spinning sensation)

Hearing lossHearing loss Tinnitus (a roaring, buzzing, or ringing Tinnitus (a roaring, buzzing, or ringing

sound in the ear)sound in the ear) A sensation of fullness in the affected A sensation of fullness in the affected

ear. ear.

Meniere’s DiseaseMeniere’s Disease

A disorder of the inner ear. Although the cause A disorder of the inner ear. Although the cause is unknown, it probably results from an is unknown, it probably results from an abnormality in the fluids of the inner ear.abnormality in the fluids of the inner ear.

Ménière’s disease is one of the most common Ménière’s disease is one of the most common causes of dizziness originating in the inner ear.causes of dizziness originating in the inner ear.

In most cases only one ear is involved, but In most cases only one ear is involved, but both ears may be affected in about 15 percent both ears may be affected in about 15 percent of patients. of patients.

Ménière’s disease typically starts between the Ménière’s disease typically starts between the ages of 20 and 50 years. Men and women are ages of 20 and 50 years. Men and women are affected in equal numbers. affected in equal numbers.