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 pinna external auditory canal tympanic 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 window malleus stapes incus

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 lBoth 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 vestibule semicircular canals cochlea

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 labyrinth membranous labyrinth

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 saccule utricle vestibule

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) maculae

THE MACULAE Each maculae contains: – Receptor cells called hair cells – A jelly-like membrane called the otolithic membrane – Calcium carbonate stones called otoliths otoliths hair 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 otoliths macula

DYNAMIC EQUILIBRIUM Detected by receptors in the semicircular canals called the crista ampullaris – Detect acceleration – Mainly respond to rotational or angular movements ampulla crista 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 ampulla crista 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 cells cupula supporting 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 nerve cochlear nerve

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 tympani scala vestibuli scala media òScala media (cochlear duct itself)  Filled with endolymph òScala tympani (tympanic canal)  Below cochlear duct  Filled with perilymph

THE COCHLEA Oval window – At the entrance of the vestibular canal Round window – At the end of the tympanic canal oval window round 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 membrane basilar membrane organ 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 membrane

SOUND TRANSMISSION Sound waves enter the external auditory canal Tympanic membrane vibrates Malleus, incus and stapes vibrate Stapes vibrates membrane on oval window tympanic membrane external auditory canal

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 duct basilar membrane scala vestibuli round window oval window perilymph stapes scala tympani

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)