Sensory System Ear: Sound & Balance

3 Parts: Outer – Middle - Inner

Outer Ear: Auricle Called the Pinna Fx: Collects sound waves Visible part of the ear, outside the head Auris latin for ear Pinna is external portion of the ear (pinna latin for wing or fin)

Outer Ear: External Auditory Canal Extends from Pinna to eardrum Fx: Transmits sound waves Aka ear canal. AKA external auditory meatus. Adults ~ 2.5 cm in length and .7 cm diameter

Outer Ear: External Auditory Canal Produces Cerumen (earwax) Fx: Traps foreign bodies Wet type dominant, dry type is recessive Cotton swaps = bad, impact wax, can cause damage to your ears.

Middle Ear: Air-filled Converts sound waves to mechanical energy Amplifies it Conducts to next chamber

Components: Tympanic membrane – Eardrum Vibrates Sound to Mechanical Energy

Perforated Eardrum: ruptured

Inflammation of the middle ear Otitis Media Painful ear infection, bacterial or viral. Usually prescribed antibiotics Inflammation of the middle ear

Components: Ossicles – 3 bones Fx: Mechanical vibration Malleus (Hammer) Incus (Anvil) Stapes (Stirrup) Fx: Mechanical vibration Ossicle means small bone

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

Adjusts pressures between middle ear & outside Drains middle ear Eustachian Tube Fx: Adjusts pressures between middle ear & outside Drains middle ear Picture – as it opens to nasopharynx

Swallowing & yawning open it Eustachian Canal Normally closed Swallowing & yawning open it Tympanic membrane will not vibrate well if pressures not equal Fluid in canal behind ear drum

If fail to open, increased pressure (pain) and infections Eustachian Canal If fail to open, increased pressure (pain) and infections Fluid in canal behind ear drum

Requires Ear Tubes – drain the excess fluid & prevent infection

Bony Chambers (fluid-filled) 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 Bony labyrinth contains perilymph

Inner Ear Membranous Labyrinth Sac contains thick fluid = Endolymph Membranous labyrinth contains endolymph

Hearing and the Inner Ear - Cochlea Snail-like shape Membranous sac contains organ of Corti

Cochlear Ducts Membranous labyrinth Perilymph Endolymph Organ of Corti Organ of corti is only found in mammals. Endolymph Organ of Corti

Organ of Corti Contains specialized hearing receptors or hair cells Embedded in basilar membrane Basilar membrane stiff structure separates two tubes in cochlea

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 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