1/24/2016 The Ear • The organ of hearing and equilibrium – Cranial nerve VIII - Vestibulocochlear – Regions The Special Senses • External ear • Middle ear Hearing and • Internal ear (labyrinth) Equilibrium External Ear Middle Internal ear • Two parts External ear (labyrinth) ear – Pinna or auricle (external structures) – External auditory meatus (car canal) Auricle • Site of cerumen (earwax) production (pinna) – Waterproofing, protection • Separated from the middle ear by the tympanic membrane Helix (eardrum) – Vibrates in response to sound waves Lobule External acoustic Tympanic Pharyngotympanic meatus membrane (auditory) tube (a) The three regions of the ear Figure 15.25a Middle Ear Epitympanic Middle Ear Superior Malleus Incus recess Lateral • Tympanic cavity Anterior – Air-filled chamber – Openings View • Tympanic membrane – covers opening to outer ear • Round and oval windows – openings to inner ear • Epitympanic recess – dead-end cavity into temporal bone of unknown function • Auditory tube – AKA Eustachian tube or pharyngotympanic tube Pharyngotym- panic tube Tensor Tympanic Stapes Stapedius tympani membrane muscle muscle (medial view) Figure 15.26 1 1/24/2016 Middle Ear Middle Ear • Auditory tube (Eustachian tube) • Otitis Media – Connects the middle ear to the nasopharynx • Equalizes pressure – Opens during swallowing and yawning Middle Ear Middle Ear • Contains auditory ossicles (bones) • Sound waves cause tympanic membrane to vibrate – Malleus • Ossicles help transmit vibrations into the inner ear – Incus – Reduce the area where force is applied – Stapes – Increases the pressure of the force enough to transfer most of the • Middle ear is air-filled; inner ear is fluid-filled energy into the liquid – Reflexive muscle action • Sound is mostly reflected from a liquid medium restricts the movement of the bones during loud noises Inner Ear Superior vestibular ganglion Inferior vestibular ganglion • Contains functional organs for hearing & equilibrium Temporal bone –Bony labyrinth - filled with perilymph Semicircular ducts in Facial nerve –Membranous labyrinth – functional component semicircular canals Vestibular • Filled with endolymph nerve • Anterior Location of various Posterior inner ear receptors Lateral Cochlear Cristae ampullares nerve in the membranous Maculae ampullae Spiral organ Utricle in (of Corti) vestibule Cochlear duct Saccule in in cochlea vestibule Stapes in Round oval window window Figure 15.27 2 1/24/2016 Inner ear - Labyrinth Superior vestibular ganglion Inferior vestibular ganglion • Temporal Labyrinth is modified to form 3 distinct regions bone Semicircular –Vestibule ducts in Facial nerve semicircular • Gravity canals Vestibular nerve • Head position Anterior • Linear acceleration and deceleration (changes in speed) Posterior –Semicircular canals Lateral Cochlear • Angular acceleration and deceleration (changes in direction) Cristae ampullares nerve –Cochlea in the membranous Maculae ampullae • Spiral organ Vibration Utricle in (of Corti) vestibule Cochlear duct Saccule in in cochlea vestibule Stapes in Round * Note: It is always the membranous labyrinth that contains the receptors oval window window Figure 15.27 Inner Ear • The cochlea – A spiral, conical, bony chamber Modiolus Cochlear nerve, – Still 2 portions of bony labyrinth enclosing a portion of membranous division of the labyrinth Bony vestibulocochlear labyrinth nerve (VIII) Membranous Spiral ganglion labyrinth Osseous spiral lamina Vestibular membrane Bony labyrinth Cochlear duct (scala media) (a) Helicotrema Figure 15.28a Inner ear Vestibular membrane Osseous spiral lamina Tectorial membrane Scala Spiral • Cochlear duct vestibuli ganglion Cavity of the cochlea is divided into 3 chambers (scala media ; – (contains Vestibular canal (scala vestibuli) contains perilymph) • Vestibular membrane endolymph) – Cochlear duct (scala media) Stria vascularis • Basilar membrane supporting Organ of Corti – Organ of hearing Spiral organ – Tympanic canal (scala tympani) (of Corti) Scala tympani Basilar (contains membrane perilymph) (b) Figure 15.28b 3 1/24/2016 Organ of Corti Tectorial membrane Inner hair cell Organ of Corti Hairs (stereocilia) Afferent nerve fibers Outer hair cells Supporting cells Fibers of cochlear nerve Basilar membrane (c) Figure 15.28c Physiology of hearing Physiology of Hearing in a Nutshell • Transduction of sound Sounds set up vibrations in air that beat against the eardrum that pushes a chain of tiny bones Mechanical energy in middle ear that press fluid in the internal ear against membranes that set up shearing forces that pull on the tiny hair cells that stimulate nearby Fluid pressure wave in inner ear neurons that give rise to the impulses that travel to the brain – and you hear. Nerve impulse (This is from your textbook) Area of High frequency (short wavelength) = high pitch high pressure Low frequency (long wavelength) = low pitch (compressed molecules) Area of Wavelength low pressure (rarefaction) Crest Pressure Trough Time (s) Air pressure Air (a) Frequency is perceived as pitch. Distance Amplitude High amplitude = loud A struck tuning fork alternately compresses Low amplitude = soft and rarefies the air molecules around it, creating alternate zones of high and low pressure. Pressure (b) Sound waves radiate outward in all directions. Time (s) (b) Amplitude (size or intensity) is perceived as loudness. Figure 15.29 Figure 15.30 4 1/24/2016 Malleus Incus Stapes vibrating Helicotrema Cochlea Auditory ossicles in oval window Malleus Incus Stapes Cochlear nerve Sound waves Perilymph Scala vestibuli Oval Helicotrema window Scala tympani 3 8 Scala 7 tympani Cochlear duct 4 2 Scala 3 5 Basilar vestibuli membrane 6 Basilar 1 2 9 membrane 1 External auditory 8 canal Spiral organ (organ of Corti) Tectorial membrane Vestibular membrane Sounds with frequencies below hearing travel through Cochlear duct the helicotrema and do not Tympanic (contains endolymph) Tympanic Round excite hair cells. membrane window membrane Sounds in the hearing range (a) Route of sound waves through the ear Secondary tympanic go through the cochlear duct, membrane vibrating 1 Sound waves vibrate 3 Pressure waves created by vibrating the basilar membrane Middle ear Auditory tube in round window the tympanic membrane. the stapes pushing on the oval and deflecting hairs on inner 2 Auditory ossicles vibrate. window move through fluid in hair cells. Pressure is amplified. the scala vestibuli. Figure 15.31a Tectorial membrane Inner hair cell Basilar membrane Hairs (stereocilia) Afferent nerve fibers Outer hair cells High-frequency sounds displace the basilar membrane near the base. Supporting cells Fibers of basilar membrane Fibers of Medium-frequency sounds displace the basilar membrane near the middle. cochlear Base Apex (short, (long, nerve stiff floppy fibers) fibers) Low-frequency sounds displace the basilar membrane near the apex. Frequency (Hz) (b) Different sound frequencies cross the basilar membrane at different locations. Basilar membrane (c) Figure 15.31b Figure 15.28c • Movement of the basilar membrane bends the hair cells Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus Midbrain (pons-medulla junction) Cochlear nuclei Medulla Vibrations Vestibulocochlear nerve Vibrations Spiral ganglion of cochlear nerve Bipolar cell Spiral organ (of Corti) Figure 15.33 5 1/24/2016 Localization of Sound Abnormalities of hearing • Conductive deafness • Timing comparison –Interference in movement of middle ear bones – Side nearest sound detects sound first • Impacted earwax, perforated eardrum or otosclerosis of the ossicles (overgrowth • Comparison of volume of bone) – High pitched = blocked by head • Sensorineural deafness – • Perceived as loudest in ear nearest the source Damage to the neural structures • Aging, prolonged exposure to loud sounds – Low pitched = curve around head • Perceived as equally loud in both ears Abnormalities of hearing Abnormalities of hearing • Otitis media • Otosclerosis Abnormalities of hearing Abnormalities of hearing • Meniere’s Disease • Tinnitus – Episodes of vertigo – Ringing, clicking, hissing, or roaring – Progressive hearing loss – Sometimes can be heard with a stethoscope (o bjective tinnitus) – – Tinnitus May occur in the same rhythm as the heartbeat – – Caused by noise-induced hearing loss, ear infections, diseases of blood Feeling of fullness or vessels, head injury, neurological problems, brain tumors, earwax… pressure in ear – Usually only in one ear 6 1/24/2016 Vestibular Apparatus Physiology of Equilibrium Otoliths Kinocilium Otolithic Stereocilia membrane • Information about position and movement of head Hair bundle – Vestibular apparatus Macula of • Utricle utricle • Saccule Vesibule Macula of saccule • Semi-circular canals Hair cells Maculae are Supporting perpendicular cells to one another Vestibular nerve fibers Figure 15.34 Vestibule Semi-Circular canals • Macula = receptor – Crista ampullaris –Utricle • Sensory receptor for dynamic equilibrium – One in the ampulla of each semicircular canals • Horizontal movements – Major stimuli are rotatory movements • Tilting the head side to side –Saccule • Vertical movements Cupula Crista Equilibrium ampullaris Endolymph • Hair bundle (kinocilium Motion Sickness plus stereocilia) – Conflicts between eye movements and equilibrium Hair cell • Nystagmus Membranous Crista • Physiologic labyrinth ampullaris Supporting Fibers of vestibular nerve cell – Involuntary eye movement, part of a reflex (a) Anatomy of a crista ampullaris in a – Preserves clear vision during rotation of the head semicircular canal • Pathologic Cupula – Abnormal eye movement – eyes move as though the head is rotating while the head is still – Caused by damage to any part of the vestibular system (b) Scanning electron micrograph of a crista ampullaris (200x) Figure 15.36a–b 7.