outer ear structures – pinna – external auditory canal – tympanic membrane boundary between...
DESCRIPTION
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 window malleus stapes incusTRANSCRIPT
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)