Ear: Sound & Balance

Sensory System

3 Parts: Outer – Middle - Inner

Outer Ear: Auricle• Called the Pinna

– Fx: Collects sound waves–Visible part of the ear, outside the head

Outer Ear: External Auditory Canal

• Extends from Pinna to eardrum– Fx: Transmits sound waves

Outer Ear: External Auditory Canal

• Produces Cerumen (earwax)–Fx: Traps foreign bodies

Middle Ear:• Air-filled• Converts sound waves to mechanical energy

• Amplifies it• Conducts to next chamber

Components:• Tympanic membrane – Eardrum– Vibrates– Sound toMechanical

Energy

Perforated Eardrum:

Otitis Media

• Inflammation of the middle ear

Components:• Ossicles – 3 bones

– Malleus (Hammer)– Incus (Anvil)– Stapes (Stirrup)

• Fx: Mechanical vibration

Middle Ear: Ossicles•

Ear Ossicles

Middle Ear:• Oval window - Tranfers mechanical vibration from middle ear to inner ear

View of OVAL WINDOW

Oval Window

Middle Ear opens to Nasopharynx via Eustachian

tube

Eustachian Tube

Fx:• Adjusts pressures between middle

ear & outside• Drains middle ear

Eustachian Canal • Normally closed• Swallowing & yawning open it• Tympanic membrane will not

vibrate well if pressures not equal

Eustachian Canal • If fail to open, increased

pressure (pain) and infections

Requires Ear Tubes – drain the excess fluid & prevent infection

Inner Ear

• Bony Chambers (fluid-filled)•Vestibule•Semicircular Canals•Cochlea

Inner Ear Bony Labyrinth

Inner Ear Bony Labyrinth

• Fluid-filled = Perilymph • Membranous sac is

suspended in the periliymph = Membranous labyrinth

Inner Ear Membranous Labyrinth

• Sac contains thick fluid = Endolymph

Hearing and the Inner Ear

- Cochlea

• Snail-like shape• Membranous sac contains organ of Corti

Cochlear DuctsPerilymph

Membranous labyrinth

EndolymphOrgan of Corti

Organ of Corti• Contains specialized hearing

receptors or hair cells• Embedded in basilar

membrane

Organ of Corti

• Hair cells covered by gel membrane (Tectorial membrane)

• Corti converts mechanical energy into electrochemical energy

Hearing Process

• Ossicles vibrate oval window

• Sets the fluids into motion (pressure waves)

Hearing Process

• Vibrate basilar membrane

• Hair cells rub tectorial membrane (bent)

Hearing Process

• Hair cells transmit impulse to cochlear nerve

• Interpretation of sound in temporal lobe

Sound Energy to Hearing Interpretation

Sound Energy Mechanical Energy

Mechanical Electrochemical

Balance: Static Equilibrium

• Position of head when not moving (which way is up)

• Membranous sacs in vestibule contain maculae

Maculae Physiology• As head moves,

otoliths roll in response to gravity

• Pulls on gel and bends hairs in receptors

Maculae Physiology• Hair cells send impulse via

vestibular nerve

• Signal to cerebellum for interpretation

Balance: Dynamic Equilibrium

• Rotation of head or movement is detected

• Membranous semicircular canals filled with endolymph

Crista Ampullaris• Membranous semicircular

canals contain crista ampullaris

Crista Ampullaris• Contains receptor cells (w/

hairs) embedded in cupula (gel-like cap)

Ampullaris Physiology• When head moves,

endolymph lags behind

• Cupula drags against endolymph current and bends hairs

Ampullaris Physiology• Stimulates hair cells to send

impulse

• Vestibular nerve sends impulse to cerebellum