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The Reason Ears Were Invented. The original function in evolution? ….Equilibrium, coordination and balance. The VESTIBULAR APPARATUS : This is where we find Equilibrium Receptors. Like the hearing “apparatus” in the cochlea the VA has HAIRS too.

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the reason ears were invented
The Reason Ears Were Invented
  • The original function in evolution? ….Equilibrium, coordination and balance.
  • The VESTIBULAR APPARATUS : This is where we find Equilibrium Receptors.
  • Like the hearing “apparatus” in the cochlea the VA has HAIRS too.

The hairs work a little differently but the result is the same we get TRANSDUCTION: this time we will transduce motion into nerve impulses.

equilibrium
Equilibrium
  • Control of coordination and balance
  • Receptors in vestibular apparatus
    • semicircular ducts contain crista
    • saccule and utricle contain macula
  • Gravitational equilibrium – perceived by macula
    • perception of head orientation
  • Dynamic or ROTATIONAL equilibrium
    • perception of motion or acceleration
      • linear acceleration perceived by macula
      • angular acceleration perceived by crista
we have 2 types of equilibrium gravitional and rotational
We Have 2 Types of Equilibrium: GRAVITIONAL and ROTATIONAL
  • GRAVITATIONAL; Mechanoreceptors in utricle and saccule detect movement of the head in vertical and horizontal planes.
  • ROTATIONAL: Mechanoreceptors in semicircular canals detect rotational /angular moment of head.
for our gravitational equilibrium
For Our Gravitational Equilibrium
  • Each MACULA has set of HAIRS embedded in otolithic membrane, a gel-like material has earstones called OTOLITHS
  • OTOLITHS are calcium salts that rolls in response to change in GRAVITY.
slide6

Hair cells project into membranous labyrinth

Membrane contains otoliths (calcium carbonate)

hair cells move against it

Utricle more sensitive to horizontal movement,

saccule to vertical

Semicircular canals arranged at right angles

to each other

Each has an ampulla in which hair cells are located

hair cells move against endolymph

slide7

Utricle and saccule

utricle- head movement away from vertical

horizontal movement

saccule- head away from horizontal

vertical acceleration

Semicircular canals- rotational acceleration

(maintain balance while turning)

Receptors for equilibrium- “hair cells”

(modified epithelium)

Cell membranes are depolarized when bent,

release transmitters

saccule and utricle
Saccule and Utricle
  • Contain macula
    • hair cells with stereocilia and onekinocilium buried in a gelatinous otolithic membrane
    • otoliths add to the density and inertia and enhance the sense of gravity and motion
what are otoliths
What are Otoliths?
  • Otoliths are like stones, they have weight or rather DENSITY.
  • Then intensify inertia
what do we mean by inertia
What Do We Mean By Inertia?
  • Inertia is Isacc Newton’s First Law of Motion .
  • It means basically, that a body in its given state of motion tends to stay that way unless stopped by force.
  • For example: A body at rest will stay at rest unless acted upon by a force OR a body in motion will stay in motion unless acted upon by a force.
macula
Macula
  • Static equilibrium - when head is tilted, weight of membrane bends the stereocilia
  • Dynamic equilibrium – in car, linear acceleration detected as otoliths lag behind
rotational equilibrium
Another part of the ear, the semicircular canals AND another receptor region called:

the CRISTA AMPULLARIS

The Crista ampullaris consists of a gelatinus cap called the cupula

ROTATIONAL Equilibrium
crista ampullaris head rotation
Crista Ampullaris - Head Rotation
  • As head turns, endolymph lags behind, pushes cupula, stimulates hair cells
what is motion sickness
What is MOTION SICKNESS?
  • When the hair cells send messages that are incongruent with what the eyes are seeing and our body is feeling, as may occur in a boat or aircraft during rough weather, motion sickness can result.
  • IT is UNKNOWN why some people suffer motion sickness while others are immune to it.
equilibrium projection pathways
Equilibrium Projection Pathways
  • Hair cells of macula sacculi, macula utriculi and semicircular ducts synapse on vestibular nerve
  • Fibers end in vestibular nucleus in pons and medulla
equilibrium projection pathways21
Equilibrium Projection Pathways
  • Information sent to 5 targets
    • cerebellar control of head and eye movements and posture
    • nuclei of CN III, IV, and VI to produce vestibulo ocular reflex
    • reticular formation control of blood circulation and posture
    • vestibulospinal tracts innervate antigravity muscles
    • thalamic relay to cerebral cortex for awareness of position and movement
conduction deafness
Conduction Deafness
  • Any condition that interferes with the transmission of vibrations to the inner ear. Normally, during this type of damage the ossicles FUSE together…can’t move.
  • Can be caused by congenital defect such as German Measles.
  • Otosclerosis-normal bone is replaced by spongy bone
sensorineural deafness
Sensorineural Deafness
  • Receptors of the ear are worn away( steriocilia on hairs damaged)
  • Occurs with normal aging BUT also in younger people exposed to high decibels.

(any level above 80 decibels will damage the organ of corti)

Some antibiotics make ears more susceptible to damage ( OTOTOXIC) streptomycin, kanamycin, gentomycin

meneire s disease
Meneire’s Disease
  • Symptoms: nausea and VERTIGO leading to progressive deafness
  • Cause not fully known but suspected is arteriolsclerosis, degeneration of cranial nerve VIII and increased pressure of the inner ear fluids.
  • This is a very uncomfortable disease as patients often cannot stand up without extreme discomfort.
otitis media
Otitis Media
  • Middle Ear Infection- When upper respiratory infections spread to the Eustacean tube.
  • Can be serious as, ear infections can spread to brain ( mastoid cells) and lead to meningitis.
  • Also, recurring ear infections can leading to fusion of the ossicles and hearing loss!
  • Myringotomy- sometimes used here.
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