OUTER EAR• Structures

– Pinna– External Auditory

Canal– Tympanic Membrane

• Boundary between outer and middle ear

• Transfers sound vibrations to bones of middle ear

– Ceruminous Glands• Specialized sweat

glands• Wax production

pinnapinna

external external auditory canalauditory canal

tympanic membranetympanic membrane

MIDDLE EAR• Region inside the tympanic

membrane• Three Ossicles

– Malleus (hammer), incus (anvil), and stapes (stirrup)• Vibrate in response to

tympanic membrane• Vibration of the stapes

causes membrane on oval window to vibrate

• Vibrations travel to inner ear through the oval windowmalleumalleu

ss

stapesstapes

incusincus

MIDDLE EAR

• Skeletal Muscles– Tensor tympani muscle

• From wall of auditory tube / inserts on malleus

– Stapedius muscle• From posterior wall of

middle ear/ inserts on stapes

Both help prevent damage due to large vibrationsBoth help prevent damage due to large vibrations

MIDDLE EAR• Eustachian Tubes (Auditory

Tubes)– Lead from middle ear to

nasopharynx– Drain fluids– Pressure equilization

INNER EAR• Consists of bony and

membranous labyrinth• Bony Labyrinth

– System of channels in the bone

– Filled with a fluid called perilymph

– 3 regions:• Vestibule• Cochlea• Semicircular canals

vestibulevestibule

semicircular semicircular canalscanals

cochleacochlea

INNER EAR• Membranous Labyrinth

– Membranous sacs and ducts– Within the bony labyrinth– Filled with a fluid called

endolymph– Floating within the perilymph

of the bony labyrinth

bony labyrinthbony labyrinth

membranous membranous labyrinthlabyrinth

BONY LABYRINTH: VESTIBULE• Region between the

semicircular canals and cochlea

• Contains two sacs:– Saccule• Continuous with the

membranous labyrinth within the cochlea

– Utricle• Continuous with the

membranous labyrinth within the semicircular canal

sacculesaccule

utricleutricle vestibulevestibule

STATIC EQUILIBRIUM

• Detected by sensory receptors in the saccule and utricle called the maculae– Detect changes in head

position– Detect linear acceleration

(changes in speed and direction)

maculaemaculae

THE MACULAE• Each maculae contains:

– Receptor cells called hair cells– A jelly-like membrane called the

otolithic membrane– Calcium carbonate stones called

otoliths

otolithsotoliths

hair cellshair cells

THE MACULAE• Cilia on the hair cells

project up into the membrane

• Head movement causes the otoliths to pull the membrane

• Movement of the membrane causes movement of the cilia

• A nerve impulse is generated by the hair cells in response

otolithsotolithsmaculamacula

DYNAMIC EQUILIBRIUM• Detected by receptors in

the semicircular canals called the crista ampullaris– Detect acceleration

– Mainly respond to rotational or angular movements

ampullaampulla

crista ampullariscrista ampullaris

THE SEMICIRCULAR CANALS• Three canals are located in

each ear– Anterior, posterior and

lateral semicircular canals– Each canal is oriented in a

different plane of direction• Allows for detection of

movement in all directions

THE SEMICIRCULAR CANALS– Each canal contains a membranous

duct filled with endolymph– Enlarged area called the ampulla at

the base of each canal– Each ampulla contains a crista

ampullaris

ampullaampulla

crista ampullariscrista ampullaris

THE CRISTA AMPULLARIS• Each crista is composed of:

– Receptor hair cells surrounded by supporting cells

– Cilia on the hair cells– A gel-like cap called the cupula

• Cilia on the hair cells project up into the cupula

hair cellshair cells

cupulacupula

supporting cellssupporting cells

ROTATIONAL MOVEMENTS

• Rotational movement of the head causes endolymph in the semicircular ducts to move

• As the endolymph swings by the crista, the cupula is bent

• Bending of the cilia causes depolarization of the hair cells nerve impulse is generated

THE VESTIBULAR NERVE

• All information regarding equilibrium coming from the maculae and the semicircular canals travels through the vestibular nerve

• The vestibular nerve joins the cochlear nerve to form the vestibulocochlear nerve (CN VIII)

vestibular vestibular nervenerve

cochlear cochlear nervenerve

SOUND

• Detected by a receptor organ in the cochlea called the organ of Corti

• Cochlea– A spiral, bony chamber– A membranous cochlear

duct runs through the center

THE COCHLEA• Cochlear duct divides the cochlea into

3 chambers:– Scala vestibuli (vestibular canal)

• Above cochlear duct• Filled with perilymph

scala tympaniscala tympani

scala vestibuliscala vestibuli

scala mediascala media

Scala mediaScala media ((cochlear duct cochlear duct itself)itself)Filled with endolymphFilled with endolymph

Scala tympaniScala tympani (tympanic(tympanic canal)canal)Below cochlear ductBelow cochlear ductFilled with perilymphFilled with perilymph

THE COCHLEA• Oval window

– At the entrance of the vestibular canal

• Round window – At the end of the tympanic canal

oval windowoval window

round windowround window

THE COCHLEAR DUCT• The roof is composed of the

vestibular membrane• The floor is composed of the

basilar membrane• Organ of Corti sits within the

cochlear duct

vestibular membranevestibular membrane

basilar membranebasilar membrane

organ of Cortiorgan of Corti

THE ORGAN OF CORTI• Contains receptor hair cells• Tectorial membrane

– A jelly-like flap lying above the hair cells

• Bending of the cilia on the hair cells causes nerve impulse generation

tectorial tectorial membranemembrane

SOUND TRANSMISSION

• Sound waves enter the external auditory canal

• Tympanic membrane vibrates

• Malleus, incus and stapes vibrate

• Stapes vibrates membrane on oval window

tympanic tympanic membranemembrane

external auditory external auditory canalcanal

SOUND TRANSMISSION• Waves form in perilymph of vestibular canal • Waves travel to perilymph of tympanic canal• Basilar membrane swings up and down• Cochlear duct begins moving• Bending of the cilia on the hair cells in the organ of Corti results in

generation of a nerve impulse

cochlear ductcochlear duct

basilar membranebasilar membrane

scala scala vestibulivestibuli

round round windowwindow

oval oval windowwindow perilymphperilymph

stapesstapes

scala scala tympanitympani

HEARING LOSS• Can be temporary or permanent• Common Causes:– Middle ear infections

• Most common in childhood• Can be relieved by a myringotomy

• Conduction Deafness– Caused by:

• Ear wax build up• Fusion of bones in the middle ear• Scarring of the tympanic membrane• A pregnant woman having German Measles during pregnancy

HEARING LOSS

• Nerve deafness– Common causes:

• Cilia on hair cells in the cochlea may wear away• Aging• Frequent exposure to loud sounds• Damage to auditory cortex of brain (temporal lobe)

HEARING IMBALANCES• Tinnitus

– Ringing or clicking sound in the ears in absense of auditory stimuli

– Symptom of cochlear nerve degeneration– Results from middle or inner ear inflammation

• Ménière’s Syndrome– Disorder affecting semicircular canals and the cochlea– Marked by fleeting but repeated attacks of vertigo, nausea,

vomiting and “howling” tinnitus– Hearing is impaired and ultimately lost– Cause is uncertain

SUMMING IT UP

• The saccule and utricle (in the vestibule) contain sensory receptors that detect static motion (change in head position and linear acceleration– These receptors are called the maculae• They contain hair cells, an otolithic membrane and

otoliths

SUMMING IT UP• The semicircular canals contain sensory receptors that

detect dynamic or rotational movement• The receptors are called crista ampullaris– The crista are found in the ampulla of the canals– Each crista contains hair cells and a cupula

• All information regarding equilibrium travels to the brain via the vestibular nerve

SUMMING IT UP• The receptor for hearing is the organ of Corti

• The cochlea contains sensory receptors for hearing– Organ of Corti is in the cochlear duct (scala media)

• Organ of Corti contains hair cells, a tectorial membrane and a basilar membrane

• All information regarding sound travels to the brain via the cochlear nerve

• The cochlear nerve and vestibular nerve unite to form Cranial Nerve VIII (Vestibulocochlear nerve)