Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Anatomy and Physiology of Hearing © 2013 Pearson Education, Inc. The Ear: Hearing and Balance • Three major areas of ear 1. External (outer) ear – hearing only 2. Middle ear (tympanic cavity) – hearing only 3. Internal (inner) ear – hearing and equilibrium • • © 2013 Pearson Education, Inc. Receptors for hearing and balance respond to separate stimuli Are activated independently Figure 15.24a Structure of the ear. Middle Internal ear External ear (labyrinth) ear Auricle (pinna) Helix Lobule External acoustic Tympanic Pharyngotympanic meatus membrane (auditory) tube The three regions of the ear © 2013 Pearson Education, Inc. External Ear • Auricle (pinna)Composed of – Helix (rim); Lobule (earlobe) – Funnels sound waves into auditory canal • External acoustic meatus (auditory canal) – Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands – Transmits sound waves to eardrum © 2013 Pearson Education, Inc. External Ear • Tympanic membrane (eardrum) – Boundary between external and middle ears – Connective tissue membrane that vibrates in response to sound – Transfers sound energy to bones of middle ear © 2013 Pearson Education, Inc. Middle Ear (Tympanic Cavity) • A small, air-filled, mucosa-lined cavity in temporal bone – Flanked laterally by eardrum – Flanked medially by bony wall containing oval (vestibular) and round (cochlear) windows © 2013 Pearson Education, Inc. Middle Ear • Epitympanic recess—superior portion of middle ear • Mastoid antrum – Canal for communication with mastoid air cells • Pharyngotympanic (auditory) tube— connects middle ear to nasopharynx – Equalizes pressure in middle ear cavity with external air pressure © 2013 Pearson Education, Inc. Figure 15.24b Structure of the ear. Oval window (deep to stapes) Entrance to mastoid antrum in the epitympanic recess Malleus (hammer) Incus Auditory (anvil) ossicles Stapes (stirrup) Tympanic membrane Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Round window Middle and internal ear © 2013 Pearson Education, Inc. Pharyngotympanic (auditory) tube Otitis Media • Middle ear inflammation – Especially in children • Shorter, more horizontal pharyngotympanic tubes • Most frequent cause of hearing loss in children – Most treated with antibiotics – Myringotomy to relieve pressure if severe © 2013 Pearson Education, Inc. Ear Ossicles • Three small bones in tympanic cavity: the malleus, incus, and stapes – Suspended by ligaments and joined by synovial joints – Transmit vibratory motion of eardrum to oval window – Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors © 2013 Pearson Education, Inc. Figure 15.25 The three auditory ossicles and associated skeletal muscles. View Superior Malleus Incus Epitympanic recess Lateral Anterior © 2013 Pearson Education, Inc. Pharyngotym- Tensor tympani panic tube muscle Tympanic Stapes Stapedius membrane muscle (medial view) Two Major Divisions of Internal Ear • Bony labyrinth – Tortuous channels in temporal bone – Three regions: vestibule, semicircular canals, and cochlea – Filled with perilymph – similar to CSF • Membranous labyrinth – Series of membranous sacs and ducts – Filled with potassium-rich endolymph © 2013 Pearson Education, Inc. Figure 15.26 Membranous labyrinth of the internal ear. Temporal bone Semicircular ducts in semicircular canals Anterior Posterior Lateral Facial nerve Vestibular nerve Cristae ampullares in the membranous ampullae Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ Utricle in vestibule Cochlear duct in cochlea Saccule in vestibule © 2013 Pearson Education, Inc. Stapes in oval window Round window Vestibule • Central egg-shaped cavity of bony labyrinth • Contains two membranous sacs 1. Saccule is continuous with cochlear duct 2. Utricle is continuous with semicircular canals • These sacs – House equilibrium receptor regions (maculae) – Respond to gravity and changes in position of head © 2013 Pearson Education, Inc. Semicircular Canals • Three canals (anterior, lateral, and posterior) that each define ⅔ circle – Lie in three planes of space • Membranous semicircular ducts line each canal and communicate with utricle • Ampulla of each canal houses equilibrium receptor region called the crista ampullaris – Receptors respond to angular (rotational) movements of the head © 2013 Pearson Education, Inc. Figure 15.26 Membranous labyrinth of the internal ear. Temporal bone Semicircular ducts in semicircular canals Anterior Posterior Lateral Facial nerve Vestibular nerve Cristae ampullares in the membranous ampullae Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ Utricle in vestibule Cochlear duct in cochlea Saccule in vestibule © 2013 Pearson Education, Inc. Stapes in oval window Round window The Cochlea • A spiral, conical, bony chamber – Size of split pea – Extends from vestibule – Coils around bony pillar (modiolus) – Contains cochlear duct, which houses spiral organ (organ of Corti) and ends at cochlear apex © 2013 Pearson Education, Inc. The Cochlea • Cavity of cochlea divided into three chambers – Scala vestibuli—abuts oval window, contains perilymph – Scala media (cochlear duct)—contains endolymph – Scala tympani—terminates at round window; contains perilymph • Scalae tympani and vestibuli are continuous with each other at helicotrema (apex) © 2013 Pearson Education, Inc. The Cochlea • The "roof" of cochlear duct is vestibular membrane • External wall is stria vascularis – secretes endolymph • "Floor" of cochlear duct composed of – Bony spiral lamina – Basilar membrane, which supports spiral organ • The cochlear branch of nerve VIII runs from spiral organ to brain © 2013 Pearson Education, Inc. Figure 15.27a Anatomy of the cochlea. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) © 2013 Pearson Education, Inc. Figure 15.27b Anatomy of the cochlea. Vestibular membrane Tectorial membrane Cochlear duct (scala media; contains endolymph) Stria vascularis Spiral organ Basilar membrane © 2013 Pearson Education, Inc. Osseous spiral lamina Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Spiral ganglion Figure 15.27c Anatomy of the cochlea. Tectorial membrane Inner hair cell Hairs (stereocilia) Afferent nerve fibers Outer hair cells Supporting cells Fibers of cochlear nerve Basilar membrane © 2013 Pearson Education, Inc. Figure 15.27d Anatomy of the cochlea. Inner hair cell Outer hair cell © 2013 Pearson Education, Inc. Properties of Sound • Sound is – Pressure disturbance (alternating areas of high and low pressure) produced by vibrating object • Sound wave – Moves outward in all directions – Illustrated as an S-shaped curve or sine wave © 2013 Pearson Education, Inc. Figure 15.28 Sound: Source and propagation. Area of high pressure (compressed molecules) Air pressure Wavelength 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. © 2013 Pearson Education, Inc. Sound waves radiate outward in all directions. Properties of Sound Waves • Frequency – Number of waves that pass given point in given time – Pure tone has repeating crests and troughs – Wavelength • Distance between two consecutive crests • Shorter wavelength = higher frequency of sound © 2013 Pearson Education, Inc. Properties of Sound • Pitch – Perception of different frequencies – Normal range 20–20,000 hertz (Hz) – Higher frequency = higher pitch • Quality – Most sounds mixtures of different frequencies – Richness and complexity of sounds (music) © 2013 Pearson Education, Inc. Properties of Sound • Amplitude – Height of crests • Amplitude perceived as loudness – Subjective interpretation of sound intensity – Normal range is 0–120 decibels (dB) – Severe hearing loss with prolonged exposure above 90 dB • Amplified rock music is 120 dB or more © 2013 Pearson Education, Inc. Figure 15.29 Frequency and amplitude of sound waves. Pressure High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch 0.01 0.02 Time (s) 0.03 Frequency is perceived as pitch. Pressure High amplitude = loud Low amplitude = soft 0.01 © 2013 Pearson Education, Inc. 0.02 Time (s) 0.03 Amplitude (size or intensity) is perceived as loudness. Transmission of Sound to the Internal Ear • Sound waves vibrate tympanic membrane • Ossicles vibrate and amplify pressure at oval window • Cochlear fluid set into wave motion • Pressure waves move through perilymph of scala vestibuli © 2013 Pearson Education, Inc. Transmission of Sound to the Internal Ear • Waves with frequencies below threshold of hearing travel through helicotrema and scali tympani to round window • Sounds in hearing range go through cochlear duct, vibrating basilar membrane at specific location, according to frequency of sound © 2013 Pearson Education, Inc. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Slide 1 Auditory ossicles Malleus Incus Stapes Cochlear nerve Oval window Scala vestibuli Helicotrema 4a Scala tympani Cochlear duct 2 3 4b Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles 3 Pressure waves created by the stapes vibrate the tympanic vibrate. Pressure is pushing on the oval amplified. membrane. window move through fluid in the scala © 2013 Pearson Education, Inc. vestibuli. 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. 4b Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Auditory ossicles Malleus Incus Stapes Slide 2 Cochlear nerve Oval window Scala vestibuli Helicotrema Scala tympani Cochlear duct Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves vibrate the tympanic membrane. © 2013 Pearson Education, Inc. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Auditory ossicles Malleus Incus Stapes Slide 3 Cochlear nerve Oval window Scala vestibuli Helicotrema Scala tympani Cochlear duct 2 Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles vibrate the tympanic vibrate. Pressure is amplified. membrane. © 2013 Pearson Education, Inc. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Auditory ossicles Malleus Incus Stapes Cochlear nerve Oval window Scala vestibuli Helicotrema Scala tympani Cochlear duct 2 3 1 Tympanic membrane Slide 4 Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles 3 Pressure waves created by the stapes vibrate the tympanic vibrate. Pressure is pushing on the oval amplified. membrane. window move through fluid in the scala © 2013 Pearson Education, Inc. vestibuli. Basilar membrane Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Auditory ossicles Malleus Incus Stapes Slide 5 Cochlear nerve Oval window Scala vestibuli Helicotrema 4a Scala tympani Cochlear duct 2 3 Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles 3 Pressure waves created by the stapes vibrate the tympanic vibrate. Pressure is pushing on the oval amplified. membrane. window move through fluid in the scala © 2013 Pearson Education, Inc. vestibuli. 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Slide 6 Auditory ossicles Malleus Incus Stapes Cochlear nerve Oval window Scala vestibuli Helicotrema 4a Scala tympani Cochlear duct 2 3 4b Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles 3 Pressure waves created by the stapes vibrate the tympanic vibrate. Pressure is pushing on the oval amplified. membrane. window move through fluid in the scala © 2013 Pearson Education, Inc. vestibuli. 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. 4b Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. Resonance of the Basilar Membrane • Fibers near oval window short and stiff – Resonate with high-frequency pressure waves • Fibers near cochlear apex longer, more floppy – Resonate with lower-frequency pressure waves • This mechanically processes sound before signals reach receptors © 2013 Pearson Education, Inc. Figure 15.30b Pathway of sound waves and resonance of the basilar membrane. 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. Fibers of basilar membrane Apex (long, floppy fibers) Base (short, stiff fibers) 20,000 © 2013 Pearson Education, Inc. 2000 200 Frequency (Hz) 20 Different sound frequencies cross the basilar membrane at different locations. Excitation of Hair Cells in the Spiral Organ • Cells of spiral organ – Supporting cells – Cochlear hair cells • One row of inner hair cells • Three rows of outer hair cells • Have many stereocilia and one kinocilium • Afferent fibers of cochlear nerve coil about bases of hair cells © 2013 Pearson Education, Inc. Figure 15.27c Anatomy of the cochlea. Tectorial membrane Inner hair cell Hairs (stereocilia) Afferent nerve fibers Outer hair cells Supporting cells Fibers of cochlear nerve Basilar membrane © 2013 Pearson Education, Inc. Excitation of Hair Cells in the Spiral Organ • Stereocilia – Protrude into endolymph – Longest enmeshed in gel-like tectorial membrane • Sound bending these toward kinocilium – Opens mechanically gated ion channels – Inward K+ and Ca2+ current causes graded potential and release of neurotransmitter glutamate – Cochlear fibers transmit impulses to brain © 2013 Pearson Education, Inc. Auditory Pathways to the Brain • Impulses from cochlea pass via spiral ganglion to cochlear nuclei of medulla • From there, impulses sent – To superior olivary nucleus – Via lateral lemniscus to Inferior colliculus (auditory reflex center) • From there, impulses pass to medial geniculate nucleus of thalamus, then to primary auditory cortex • Auditory pathways decussate so that both cortices receive input from both ears © 2013 Pearson Education, Inc. Figure 15.32 The auditory pathway. Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (ponsmedulla junction) Midbrain Cochlear nuclei Vibrations Medulla Vestibulocochlear nerve Vibrations Spiral ganglion of cochlear nerve Bipolar cell Spiral organ © 2013 Pearson Education, Inc. Auditory Processing • Pitch perceived by impulses from specific hair cells in different positions along basilar membrane • Loudness detected by increased numbers of action potentials that result when hair cells experience larger deflections • Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears © 2013 Pearson Education, Inc. Equilibrium and Orientation • Vestibular apparatus – Equilibrium receptors in semicircular canals and vestibule – Vestibular receptors monitor static equilibrium – Semicircular canal receptors monitor dynamic equilibrium © 2013 Pearson Education, Inc. Maculae • Sensory receptors for static equilibrium • One in each saccule wall and one in each utricle wall • Monitor the position of head in space, necessary for control of posture • Respond to linear acceleration forces, but not rotation • Contain supporting cells and hair cells • Stereocilia and kinocilia are embedded in the otolith membrane studded with otoliths (tiny CaCO3 stones) © 2013 Pearson Education, Inc. Figure 15.33 Structure of a macula. Kinocilium Stereocilia Macula of utricle Macula of saccule Otolith Otoliths membrane Hair bundle Hair cells © 2013 Pearson Education, Inc. Vestibular nerve fibers Supporting cells Maculae • Maculae in utricle respond to horizontal movements and tilting head side to side • Maculae in saccule respond to vertical movements • Hair cells synapse with vestibular nerve fibers © 2013 Pearson Education, Inc. Activating Maculae Receptors • Hair cells release neurotransmitter continuously – Movement modifies amount they release • Bending of hairs in direction of kinocilia – Depolarizes hair cells – Increases amount of neurotransmitter release – More impulses travel up vestibular nerve to brain © 2013 Pearson Education, Inc. Activating Maculae Receptors • Bending away from kinocilium – Hyperpolarizes receptors – Less neurotransmitter released – Reduces rate of impulse generation • Thus brain informed of changing position of head © 2013 Pearson Education, Inc. Figure 15.34 The effect of gravitational pull on a macula receptor cell in the utricle. Otolith membrane Kinocilium Stereocilia Receptor potential Nerve impulses generated in vestibular fiber © 2013 Pearson Education, Inc. Depolarization When hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials. Hyperpolarization When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency. The Crista Ampullares (Crista) • Sensory receptor for rotational acceleration – One in ampulla of each semicircular canal – Major stimuli are rotational movements • Each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula • Dendrites of vestibular nerve fibers encircle base of hair cells © 2013 Pearson Education, Inc. Figure 15.35a–b Location, structure, and function of a crista ampullaris in the internal ear. Ampullary cupula Crista ampullaris Endolymph Hair bundle (kinocilium plus stereocilia) Membranous labyrinth Crista ampullaris Fibers of vestibular nerve Hair cell Supporting cell Anatomy of a crista ampullaris in a semicircular canal Section of ampulla, filled with endolymph Cupula Fibers of vestibular nerve At rest, the cupula stands upright. © 2013 Pearson Education, Inc. Scanning electron micrograph of a crista ampullaris (200x) Flow of endolymph During rotational acceleration, As rotational movement slows, endolymph moves inside the endolymph keeps moving in the semicircular canals in the direction direction of rotation. Endolymph flow opposite the rotation (it lags behind due bends the cupula in the opposite to inertia). Endolymph flow bends the direction from acceleration and cupula and excites the hair cells. inhibits the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration Activating Crista Ampullaris Receptors • Cristae respond to changes in velocity of rotational movements of the head • Bending of hairs in cristae causes – Depolarizations, and rapid impulses reach brain at faster rate © 2013 Pearson Education, Inc. Activating Crista Ampullaris Receptors • Bending of hairs in the opposite direction causes – Hyperpolarizations, and fewer impulses reach the brain • Thus brain informed of rotational movements of head © 2013 Pearson Education, Inc. Figure 15.35c Location, structure, and function of a crista ampullaris in the internal ear. Section of ampulla, filled with endolymph Cupula Fibers of vestibular nerve At rest, the cupula stands upright. Flow of endolymph During rotational acceleration, As rotational movement slows, endolymph moves inside the endolymph keeps moving in the semicircular canals in the direction direction of rotation. Endolymph flow opposite the rotation (it lags behind due bends the cupula in the opposite to inertia). Endolymph flow bends the direction from acceleration and cupula and excites the hair cells. inhibits the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration © 2013 Pearson Education, Inc. Vestibular Nystagmus • Strange eye movements during and immediately after rotation – Often accompanied by vertigo • As rotation begins eyes drift in direction opposite to rotation, then CNS compensation causes rapid jump toward direction of rotation • As rotation ends eyes continue in direction of spin then jerk rapidly in opposite direction © 2013 Pearson Education, Inc. Equilibrium Pathway to the Brain • Equilibrium information goes to reflex centers in brain stem – Allows fast, reflexive responses to imbalance • Impulses travel to vestibular nuclei in brain stem or cerebellum, both of which receive other input • Three modes of input for balance and orientation: – Vestibular receptors – Visual receptors – Somatic receptors © 2013 Pearson Education, Inc. Figure 15.36 Neural pathways of the balance and orientation system. Input: Information about the body’s position in space comes from three main sources and is fed into two major processing areas in the central nervous system. Somatic receptors (skin, muscle and joints) Vestibular receptors Visual receptors Cerebellum Vestibular nuclei (brain stem) Central nervous system processing Oculomotor control (cranial nerve nuclei III, IV, VI) Spinal motor control (cranial nerve XI nuclei and vestibulospinal tracts) (eye movements) (neck, limb, and trunk movements) Output: Responses by the central nervous system provide fast reflexive control of the muscles serving the eyes, neck, limbs, and trunk. © 2013 Pearson Education, Inc. Motion Sickness • Sensory input mismatches – Visual input differs from equilibrium input – Conflicting information causes motion sickness • Warning signs are excess salivation, pallor, rapid deep breathing, profuse sweating • Treatment with antimotion drugs that depress vestibular input such as meclizine and scopolamine © 2013 Pearson Education, Inc. Homeostatic Imbalances of Hearing • Conduction deafness – Blocked sound conduction to fluids of internal ear • Impacted earwax, perforated eardrum, otitis media, otosclerosis of the ossicles • Sensorineural deafness – Damage to neural structures at any point from cochlear hair cells to auditory cortical cells – Typically from gradual hair cell loss © 2013 Pearson Education, Inc. Treating Deafness • Research trying to prod supporting cell differentiation into hair cells to treat sensorineural deafness • Cochlear implants for congenital or age/noise cochlear damage – Convert sound energy into electrical signals – Inserted into drilled recess in temporal bone – So effective that deaf children can learn to speak © 2013 Pearson Education, Inc. Homeostatic Imbalances of Hearing • Tinnitus – Ringing or clicking sound in ears in absence of auditory stimuli – Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin • Ménière's syndrome: labyrinth disorder that affects cochlea and semicircular canals – Causes vertigo, nausea, and vomiting © 2013 Pearson Education, Inc. Developmental Aspects • All special senses are functional at birth • Chemical senses—few problems occur until fourth decade, when these senses begin to decline – Odor and taste detection poor after 65 • Vision—optic vesicles protrude from diencephalon during fourth week of development – Vesicles indent to form optic cups; their stalks form optic nerves – Later, lens forms from ectoderm © 2013 Pearson Education, Inc. Developmental Aspects • Vision not fully functional at birth • Babies hyperopic, see only gray tones, eye movements uncoordinated, tearless for 2 weeks • Depth perception, color vision well developed by age three; emmetropic eyes developed by year six • With age, lens loses clarity, dilator muscles less efficient, visual acuity drastically decreased by age 70 and lacrimal glands less active so eyes dry, more prone to infection © 2013 Pearson Education, Inc. Developmental Aspects • Ear development begins in three-week embryo • Inner ears develop from otic placodes, which invaginate into otic pit and otic vesicle • Otic vesicle becomes membranous labyrinth, and surrounding mesenchyme becomes bony labyrinth • Middle ear structures develop from pharyngeal pouches • Branchial groove develops into outer ear structures © 2013 Pearson Education, Inc. Developmental Aspects • Newborns can hear but early responses reflexive • Language skills tied to ability to hear well • Congenital abnormalities common – Missing pinnae, closed or absent external acoustic meatuses – Maternal rubella causes sensorineural deafness © 2013 Pearson Education, Inc. Developmental Aspects • Few ear problems until 60s when deterioration of spiral organ noticeable • Hair cell numbers decline with age – Presbycusis occurs first • Loss of high pitch perception • Type of sensorineural deafness © 2013 Pearson Education, Inc.