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←—— Semicircular Semicircular Canals Canals ←—— ←—— Cochlea Cochlea Oval Oval Window Window Round Round Window Window. THE INNER EAR[r]

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DEPARTMENT OF ANATOMY

THE EAR

THE EARTHE EAR

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Ludwig van Beethoven (1770-1827)

9 th Symphony (Choral)

Composed when he was profoundly deaf.

THE EAR

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THE EAR

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Anatomy of Ear Outer Outer Ear Ear Middle Middle Ear Ear Inner Inner Ear Ear

THE EXTERNAL EAR

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THE EXTERNAL EAR

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THE EXTERNAL EAR

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THE EXTERNAL EAR

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THE EXTERNAL EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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Middle Ear (Tympanic Cavity)

A small, air-filled, mucosa-lined cavity in the petrous portion of the temporal bone

Flanked laterally by the eardrum and medially by a bony wall with two openings, the oval (vestibular) and round (cochlear) windows

Epitympanic recess -superior portion of the middle ear containing the entrance to the masotid antrum

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Middle Ear (Tympanic Cavity)

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

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THE MIDDLE EAR

1 d=10mm-10mm 55-65mm2

3 1400 (sup wall canal)

1 d=10mm-10mm 55-65mm2

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THE MIDDLE EAR

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THE MIDDLE EAR

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Tympanic Membrane (Ear Drum)

micrograph

(view from inside)

←—————

Tympamium

←———

←——— Malleus and Malleus and ligaments

ligaments

THE MIDDLE EAR

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The Ossicles

Malleus

Malleus ———— → → ←—— ←—— Incus Incus ←—— ←—— Stapes Stapes

THE MIDDLE EAR

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THE MIDDLE EAR

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Ossicles

(Micrographs)

Malleus

MalleusIncusIncus

Stape

s

Malleus

Malleus IncusIncus

Stapes Stapes Tympaniu Tympaniu m m

THE MIDDLE EAR

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THE INNER EAR

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THE INNER EAR

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Anatomy of Ear

Inner Ear

THE INNER EAR

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THE INNER EAR

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Anatomy of Inner Ear

←——

←—— Semicircular Semicircular Canals Canals ←—— ←—— Cochlea Cochlea Oval Oval Window Window Round Round Window Window

THE INNER EAR

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Cochlea

(micrograph)

“The Snail”

• o~ oval window • r~ round window

2 mm

THE INNER EAR

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THE INNER EAR

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Microstructure of Cochlea

Basilar

Basilar ——————→ ——————→ Membrane

Membrane ↑↑

Organ of

Corti

Auditory Nerve

Auditory Nerve → → →

→

↑

THE INNER EAR

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Stereocilia (Hair Cells)

THE INNER EAR

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Outer Hair Cell in Cross Section

THE INNER EAR

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Inner Hair Cells Afferent Afferent EfferentEfferent Synapse ⇘

THE INNER EAR

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Organ of Corti and Basilar Membrane

OuterOuter

←——— ←——— CellsCells Hair Hair ←—————

←————— Inner Hair Inner Hair Cells

Cells

Vibration

THE INNER EAR

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Detail of Hair Cell

Stereocilia

THE INNER EAR

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1 St=55-65mm2=20*Ss

2 FleverOssicle ↑1-3

1 St=55-65mm2=20*Ss

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THE INNER EAR

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THE INNER EAR

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Vibration

Vibration )))) ))

))

Action of Hair Cell

Hair Cell Hair Cell Depolarizes Depolarizes Neurotransmitt Neurotransmitt er released er released Hair Cell Hair Cell Nerve Nerve

THE INNER EAR

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Function of Stereocilia Stimulation in HC Causes neuro-transmitter to stimulate neuron in Auditory Nerve

THE INNER EAR

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Properties of Sound

Sound - a pressure disturbance (alternating areas of high and low pressure or rarefaction and

compression) originating from a vibrating object Represented by a sine wave having wavelength, frequency, and amplitude

Frequency – the number of waves that pass a given point in a given time (cycles/sec = Hz)

Pitch – perception of different frequencies (we hear from 20–20,000 Hz

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Properties of Sound

Sound intensity is

measured in logarithmic units called decibels (dB – 0dB→130dB)

I(W/m2)=P/A – ß=lgI/I

0

Frequency = pitch

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Neuronal Response to Sound

• Frequency → Where? The location

where in the Cochlea the stereocilia are stimulated.

• Intensity → How many? The number of

HC that are stimulated by the sound determines the perceived loudness.

THE INNER EAR

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Neuronal Decoding of Sound (Schematic) Frequency Frequency response response localized in localized in Cochlea Cochlea High Frequency Low Frequency

THE INNER EAR

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Frequency Response of Hair Cells THE INNER EAR

THE INNER EAR

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THE MIDDLE EAR

1 ten tymp mem p perilym↑

3 V3

1 ten tymp mem p perilym↑

3 V3

1 ↓ten tymp mem. 2 ↓p perilym

3 VII

1 ↓ten tymp mem. 2 ↓p perilym

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THE INNER EAR

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THE MIDDLE EAR

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80/20Repeated acoustic trauma can cause

permanent and profound hearing loss or deafness.

If you have experienced temporary hearing loss due to loud sounds you have had a warning.

Stereocilia regenerate daily.

THE INNER EAR

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Hearing Loss due to Over Stimulation causes Excitotoxicity

Too much Ca

Too much Ca2+2+ poisons the neuron.

poisons the neuron.

THE INNER EAR

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Extreme Acoustic Trauma Control, not Control, not exposed exposed After After Exposure Exposure

Guinea Pig Stereocilia damage (120 dB

sound)

THE INNER EAR

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How you protect yourself? Ear Plugs Ear Plugs Wear Wear Them! Them! Wear Them!

Wear Them!Wear Them!

Wear Them!

THE INNER EAR

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Mechanisms of Equilibrium and Orientation

Vestibular apparatus – inner ear equilibrium

receptors in the semicircular canals and vestibule (maintains orientation and balance)

Two functional groups of receptors:

Vestibular receptors (maculae) monitor static equilibrium

Semicircular canal receptors (cristae)

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Maculae - Static Equilibrium

Each macula is a flat section of epithelial tissue containing supporting cells and hair cells

Each hair cell has stereocilia (microvilli) and a kinocilium embedded in the otolithic membrane Otolithic membrane is a jellylike mass containing tiny CaCO3 stones (crystals) called otoliths

Utricular hairs respond to horizontal movement

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Anatomy of Maculae

Otolithic movement in one direction depolarizes

vestibular nerve fibers and increases the number of

action potentials generated Movement in the opposite direction hyperpolarizes vestibular nerve fibers and reduces the rate of impulse propagation

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Crista Ampullaris - Dynamic Equilibrium

The crista ampullaris (or crista) is located in the ampulla

of each semicircular canal and responds to angular

movements Each crista has support cells and hair cells

that extend into a gel-like mass called the cupula

Dendrites of vestibular nerve fibers encircle the base of

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Crista Ampullaris

Cristae respond to changes in velocity of rotatory movements of the head Directional bending of hair cells in the cristae causes either depolarizations (rapid impulses) or hyperpolarizations (fewer impulses)

Impulses in the vestibular nerve component of cranial

nerve VIII travel to the vestibular nuclear complex

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THANK YOU VERY MUCH FOR THANK YOU VERY MUCH FOR

YOUR ATTENTION !!! YOUR ATTENTION !!!

MERCI DE VOTRE ATTENTION !!! MERCI DE VOTRE ATTENTION !!!

THANK YOU VERY MUCH FOR

YOUR ATTENTION !!!

MERCI DE VOTRE ATTENTION !!!

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