Download The Ear

The Ear’s Role in
Balance and
Equilibrium
The Ear
 Houses two senses
1. Hearing
2. Equilibrium (balance)
 Receptors are mechanoreceptors
 Different organs house receptors
for each sense
Anatomy of the Ear
 The ear is divided into three
areas
1. External ear
2. Middle ear
3. Inner ear
The External Ear
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Involved in hearing only
Structures of the external ear
1. Pinna (auricle)
2. External auditory canal
The Middle Ear

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Air-filled cavity within the temporal bone
Only involved in the sense of hearing
Two tubes are associated with the inner ear
 The opening from the auditory canal is covered by the tympanic
membrane
 The auditory tube connecting the middle ear with the throat
 Allows for equalizing pressure during yawning or swallowing
 This tube is otherwise collapsed
Three bones span the cavity
1. Malleus (hammer)
2. Incus (anvil)
3. Stapes (stirrup)
Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear
The Inner Ear or Bony Labyrinth
 Includes sense organs
for hearing and balance
 Filled with perilymph
 A maze of bony
chambers within the
temporal bone
Organs of the Inner Ear
Semicircular canals – organ for dynamic
equilibrium
Cochlea – organ for
hearing
Vestibule – organ for
static equilibrium
Organs of Equilibrium

Receptor cells are in two structures
1. Vestibule (static)
2. Semicircular canals (dynamic)

Equilibrium has two functional parts
1. Static equilibrium
2. Dynamic equilibrium
Static Equilibrium
receptors are in the vestibule
Maculae – receptors on the
membranes of the
vestibule
 Report on the position of
the head
 Send information via the
vestibular nerve
Dynamic Equilibrium
receptors are in the semicircular
canals
Crista ampullaris – receptors in the
semicircular canals
 Tuft of hair cells
 Cupula (gelatinous cap) covers the
hair cells
Action of angular head movements
 The cupula stimulates the hair cells
 An impulse is sent via the vestibular
nerve to the cerebellum
Review of the balance and
equilibrium organs in the inner ear
I.
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
angular head movements

The organ is the semicircular
canals

The receptor inside the semicircular
canals is the crista ampullaris
Symptoms of Meniere’s Disease
 The symptoms of Ménière’s disease are
episodic rotational vertigo (attacks of a
spinning sensation)
 Hearing loss
 Tinnitus (a roaring, buzzing, or ringing
sound in the ear)
 A sensation of fullness in the affected
ear.
Meniere’s Disease
 A disorder of the inner ear. Although the cause
is unknown, it probably results from an
abnormality in the fluids of the inner ear.
 Ménière’s disease is one of the most common
causes of dizziness originating in the inner ear.
 In most cases only one ear is involved, but
both ears may be affected in about 15 percent
of patients.
 Ménière’s disease typically starts between the
ages of 20 and 50 years. Men and women are
affected in equal numbers.