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THE SPECIAL SENSES Hearing and Equilibrium THE EAR The organ of hearing and equilibrium Cranial nerve VIII - Vestibulocochlear Regions External ear Middle ear Internal ear (labyrinth) External ear Middle Internal ear ear (labyrinth) Auricle (pinna) Helix Lobule External Tympanic Pharyngotympanic acoustic membrane (auditory) tube meatus (a) The three regions of the ear Figure 15.25a Middle Ear Malleus Superior Epitympanic Incus recess Lateral Anterior View Pharyngotympanic tube Tensor tympani muscle Copyright © 2010 Pearson Education, Inc. Tympanic membrane (medial view) Stapes Stapedius muscle Figure 15.26 MIDDLE EAR Auditory tube Connects the middle ear to the nasopharynx Equalizes pressure Opens during swallowing and yawning Otitis media INNER EAR Contains functional organs for hearing & equilibrium Bony labyrinth Membranous labyrinth Superior vestibular ganglion Inferior vestibular ganglion Temporal bone Semicircular ducts in semicircular canals Facial nerve Vestibular nerve Anterior Posterior Lateral Cochlear nerve Maculae Cristae ampullares in the membranous ampullae Spiral organ (of Corti) Cochlear duct in cochlea Utricle in vestibule Saccule in vestibule Stapes in oval window Round window Figure 15.27 INNER EAR - BONY LABYRINTH Three distinct regions Vestibule Gravity Head position Linear acceleration and deceleration Semicircular canals Angular acceleration and deceleration Cochlea Vibration Superior vestibular ganglion Inferior vestibular ganglion Temporal bone Semicircular ducts in semicircular canals Facial nerve Vestibular nerve Anterior Posterior Lateral Cochlear nerve Maculae Cristae ampullares in the membranous ampullae Spiral organ (of Corti) Cochlear duct in cochlea Utricle in vestibule Saccule in vestibule Stapes in oval window Round window Figure 15.27 INNER EAR The cochlea A spiral, conical, bony chamber Vestibular canal (scala vestibuli) Cochlear duct (scala media) Tympanic canal (scala tympani) Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) (a) Helicotrema Figure 15.28a INNER EAR Cavity of the cochlea is divided into 3 chambers Vestibular canal (scala vestibuli) Vestibular membrane Cochlear duct (scala media) Basilar membrane supporting Organ of Corti Tympanic canal (scala tympani) Vestibular membrane Osseous spiral lamina Tectorial membrane Cochlear duct (scala media; contains endolymph) Scala vestibuli (contains perilymph) Spiral ganglion Stria vascularis Spiral organ (of Corti) Basilar membrane Scala tympani (contains perilymph) (b) Copyright © 2010 Pearson Education, Inc. Figure 15.28b Tectorial membrane Organ of Corti Hairs (stereocilia) Inner hair cell Afferent nerve fibers Outer hair cells Supporting cells Fibers of cochlear nerve (c) Basilar membrane Figure 15.28c PHYSIOLOGY OF HEARING Transduction of sound Mechanical energy in middle ear Fluid pressure wave in inner ear Nerve impulse PHYSIOLOGY OF HEARING IN A NUTSHELL Sounds set up vibrations in air that beat against the eardrum that pushes a chain of tiny bones that press fluid in the internal ear against membranes that set up shearing forces that pull on the tiny hair cells that stimulate nearby neurons that give rise to the impulses that travel to the brain – and you hear. (This is from your textbook) Air pressure Wavelength Area of high pressure (compressed molecules) Area of low pressure (rarefaction) Crest Trough Distance Amplitude A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. (b) Sound waves radiate outward in all directions. Figure 15.29 Pressure High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch Time (s) (a) Frequency is perceived as pitch. Pressure High amplitude = loud Low amplitude = soft Time (s) (b) Amplitude (size or intensity) is perceived as loudness. Copyright © 2010 Pearson Education, Inc. Figure 15.30 Malleus Incus Stapes vibrating Helicotrema in oval window Cochlea Sound waves Perilymph 3 7 4 5 1 2 6 9 External auditory canal 8 Scala tympani Scala vestibuli Basilar membrane 8 Spiral organ (organ of Corti) Tectorial membrane Vestibular membrane Cochlear duct (contains endolymph) Tympanic membrane Secondary tympanic membrane vibrating in round window Middle ear Auditory tube Auditory ossicles Malleus Incus Stapes Cochlear nerve Scala vestibuli Oval window Helicotrema 2 3 Scala tympani Cochlear duct Basilar membrane 1 Tympanic Round membrane window (a) Route of sound waves through the ear 1 Sound waves vibrate the tympanic membrane. 2 Auditory ossicles vibrate. Pressure is amplified. Copyright © 2010 Pearson Education, Inc. 3 Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. Figure 15.31a Basilar membrane High-frequency sounds displace the basilar membrane near the base. Medium-frequency sounds displace the basilar membrane near the middle. Low-frequency sounds displace the basilar membrane near the apex. (b) Different sound frequencies cross the basilar membrane at different locations. Copyright © 2010 Pearson Education, Inc. Fibers of basilar membrane Apex (long, floppy fibers) Base (short, stiff fibers) Frequency (Hz) Figure 15.31b Tectorial membrane Inner hair cell Hairs (stereocilia) Afferent nerve fibers Outer hair cells Supporting cells Fibers of cochlear nerve (c) Copyright © 2010 Pearson Education, Inc. Basilar membrane Figure 15.28c Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (pons-medulla junction) Midbrain Cochlear nuclei Vibrations Medulla Vestibulocochlear nerve Vibrations Spiral ganglion of cochlear nerve Bipolar cell Spiral organ (of Corti) Figure 15.33 LOCALIZATION OF SOUND Timing comparison Side nearest sound detects sound first Comparison of volume High pitched = blocked by head Low pitched = curve around head ABNORMALITIES OF HEARING Conductive deafness Interference in movement of middle ear bones Impacted earwax, perforated eardrum or otosclerosis of the ossicles Sensorineural deafness Damage to the neural structures Aging, prolonged exposure to loud sounds ABNORMALITIES OF HEARING Otitis media ABNORMALITIES OF HEARING Otosclerosis ABNORMALITIES OF HEARING Meniere’s Disease ABNORMALITIES OF HEARING Tinnitus PHYSIOLOGY OF EQUILIBRIUM Information about position and movement of head Vestibular apparatus Utricle Vesibule Saccule Semi-circular canals Vestibular Apparatus Kinocilium Stereocilia Otoliths Otolithic membrane Hair bundle Macula of utricle Macula of saccule Hair cells Maculae are perpendicular to one another Supporting cells Vestibular nerve fibers Figure 15.34 VESTIBULE Macula Utricle Horizontal movements Tilting the head side to side Saccule Vertical movements SEMI-CIRCULAR CANALS Crista ampullaris Sensory receptor for dynamic equilibrium One in the ampulla of each semicircular canal Major stimuli are rotatory movements Cupula Crista ampullaris Endolymph Hair bundle (kinocilium plus stereocilia) Hair cell Crista Membranous ampullaris labyrinth Fibers of vestibular nerve (a) Anatomy of a crista ampullaris in a semicircular canal Supporting cell Cupula (b) Scanning electron micrograph of a crista ampullaris (200x) Copyright © 2010 Pearson Education, Inc. Figure 15.36a–b MOTION SICKNESS Conflicts between eye movements and equilibrium Nystagmus Slow component Fast component QUESTIONS?