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Ch. 15 Special Senses: Hearing Slides mostly © Marieb & Hoehn 9 th ed. Other slides by WCR.

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Presentation on theme: "Ch. 15 Special Senses: Hearing Slides mostly © Marieb & Hoehn 9 th ed. Other slides by WCR."— Presentation transcript:

1 Ch. 15 Special Senses: Hearing Slides mostly © Marieb & Hoehn 9 th ed. Other slides by WCR

2 © 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 Receptors for hearing and balance respond to separate stimuli Are activated independently

3 © 2013 Pearson Education, Inc. Figure 15.24a Structure of the ear. External ear Middle ear Internal ear (labyrinth) Auricle (pinna) Helix Lobule External acoustic meatus Tympanic membrane Pharyngotympanic (auditory) tube The three regions of the ear

4 © 2013 Pearson Education, Inc. External Ear Auricle (pinna) & external acoustic meatus (auditory canal) –Funnel sound waves to eardrum 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

5 © 2013 Pearson Education, Inc. Middle Ear Air-filled (usually), mucosa-lined cavity in temporal bone –Flanked laterally by eardrum –Remaining borders are formed by by temporal bone –Oval window, round windows: covered connections to the inner ear Contains 3 bones, 2 muscles Pharyngotympanic (auditory) tube –Connects middle ear to nasopharynx –Equalizes pressure in middle ear cavity with external air pressure

6 © 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

7 © 2013 Pearson Education, Inc. Figure 15.24b Structure of the ear. Oval window (deep to stapes) Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Pharyngotympanic (auditory) tube Entrance to mastoid antrum in the epitympanic recess Auditory ossicles Tympanic membrane Round window Stapes (stirrup) Incus (anvil) Malleus (hammer) Middle and internal ear

8 © 2013 Pearson Education, Inc. 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

9 © 2013 Pearson Education, Inc. Figure The three auditory ossicles and associated skeletal muscles. View Superior Anterior Lateral IncusMalleusEpitympanic recess Pharyngotym- panic tube Tensor tympani muscle Tympanic membrane (medial view) Stapes Stapedius muscle

10 © 2013 Pearson Education, Inc. 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

11 © 2013 Pearson Education, Inc. Figure Membranous labyrinth of the internal ear. Temporal bone Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ Cochlear duct in cochlea Round window Stapes in oval window Saccule in vestibule Utricle in vestibule Cristae ampullares in the membranous ampullae Lateral Posterior Anterior Semicircular ducts in semicircular canals

12 © 2013 Pearson Education, Inc. The Cochlea Spiral, conical, bony chamber –Size of split pea, goes from base to apex –Contains cochlear duct, which houses organ of Corti (spiral organ) Cavity of cochlea divided into three chambers –Scala vestibuli—abuts oval window & stapes, contains perilymph –Scala media (cochlear duct)—contains endolymph –Scala tympani—terminates at round window; contains perilymph Scala tympani, scala vestibuli connect with each other at helicotrema (apex)

13 © 2013 Pearson Education, Inc. The Cochlea Cochlear duct (scala media) is sandwiched between scala vestibuli & scala tympani "Floor" of cochlear duct formed by basilar membrane, which supports organ of Corti (spiral organ) Cochlear branch of nerve VIII runs from cochlea to brain

14 © 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)

15 © 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 Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Osseous spiral lamina Spiral ganglion

16 © 2013 Pearson Education, Inc. Tectorial membrane Hairs (stereocilia) Outer hair cells Supporting cells Inner hair cell Afferent nerve fibers Fibers of cochlear nerve Basilar membrane Figure 15.27c Anatomy of the cochlea.

17 © 2013 Pearson Education, Inc. Figure 15.27d Anatomy of the cochlea. Inner hair cell Outer hair cell

18 © 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

19 © 2013 Pearson Education, Inc. Figure Sound: Source and propagation. Area of high pressure (compressed molecules) Area of low pressure (rarefaction) Wavelength Amplitude Distance Air pressure A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. Sound waves radiate outward in all directions.

20 © 2013 Pearson Education, Inc. Properties of Sound Waves Frequency –Number of waves that pass given point in given time –Wavelength Distance between two consecutive crests Shorter wavelength = higher frequency of sound –Frequency range of normal (healthy) hearing: 20 – 20,000 Hertz (Hz) Pitch –Perception of frequency: higher frequency = higher pitch Most sounds are mixtures of many different frequencies simultaneously

21 © 2013 Pearson Education, Inc. Properties of Sound Amplitude –Height of crests Loudness = perception of amplitude –Subjective interpretation of sound intensity –Normal range is 0–120 decibels (dB) –Severe hearing loss with prolonged exposure above 90 dB –Loud music is 120 dB or more

22 © 2013 Pearson Education, Inc. Figure Frequency and amplitude of sound waves. High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch Pressure Time (s) Frequency is perceived as pitch. High amplitude = loud Time (s) Low amplitude = soft Amplitude (size or intensity) is perceived as loudness. Pressure

23 © 2013 Pearson Education, Inc. Transmission of Sound to the Internal Ear Sound waves vibrate tympanic membrane Ossicles vibrate and concentrate the energy (amplify the pressure) at stapes footplate in oval window Cochlear fluid set into wave motion Pressure waves move through perilymph of scala vestibuli Basilar membrane is “mechanically tuned”: different parts vibrate most (i.e. resonate) in response to different frequencies

24 © 2013 Pearson Education, Inc. Basilar Membrane Tuning (Resonance) 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 Thus basilar membrane “maps” different frequencies to different places along its length. –The “place theory” of hearing is most true for disciminating high frequencies.

25 © 2013 Pearson Education, Inc. Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Slide 1 Tympanic membrane Round window Auditory ossicles Oval window Cochlear nerve Scala vestibuli Scala tympani Cochlear duct Basilar membrane Route of sound waves through the ear Malleus IncusStapes Helicotrema 3 4a 4b Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. Sound waves vibrate the tympanic membrane. Auditory ossicles vibrate. Pressure is amplified. 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. 4a 4b

26 © 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. Different sound frequencies cross the basilar membrane at different locations. Apex (long, floppy fibers) Fibers of basilar membrane Base (short, stiff fibers) 20 20,000 Frequency (Hz)

27 © 2013 Pearson Education, Inc. 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

28 © 2013 Pearson Education, Inc. Figure 15.27c Anatomy of the cochlea. Tectorial membrane Hairs (stereocilia) Outer hair cells Supporting cells Inner hair cell Afferent nerve fibers Fibers of cochlear nerve Basilar membrane

29 © 2013 Pearson Education, Inc. Excitation of Hair Cells in the Spiral Organ Stereocilia protrude from hair cells, some embed in tectorial membrane above Passing pressure wave causes deflection of basilar membrane Shearing action of basilar membrane and tectorial membrane causes cilia to bend Opens mechanically gated ion channels via pull on tip links –Inward current causes graded potential and release of neurotransmitter glutamate from hair cell onto sensory neuron Cochlear fibers transmit impulses to brain

30 Source: Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Siegel GJ, Agranoff BW, Albers RW, et al., editors; Downloaded from Hair cell transduction by ion channel opening

31 © 2011 Pearson Education, Inc. Sensory pathway for hearing 1.Hair cells in specific area of basilar membrane become stimulated 2.Sensory neuron axons (cell bodies in spiral ganglion) make up cochlear branch of vestibulocochlear nerve (VIII) 3.Sensory neuron axons synapse onto neurons in cochlear nucleus (medulla oblongata) 4.Information ascends bilaterally (often synapsing on the way) to inferior colliculus (midbrain) 5.Inferior colliculus neurons synapse at medial geniculate nucleus (thalamus) 6.Projection fibers from thalamus reach primary auditory cortex (temporal lobe)

32 © 2013 Pearson Education, Inc. Auditory pathway Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (pons- medulla junction) Cochlear nuclei Midbrain Medulla Vestibulocochlear nerve Spiral ganglion of cochlear nerve Bipolar cell Spiral organ Vibrations

33 Tonotopic organization Different frequency sounds excite different basilar membrane regions (apex: low frequencies; base: high frequencies) Cochlear nucleus (first auditory area in CNS) has a “map” of basilar membrane, i.e. frequency map: tonotopic map Tonotopic map seen in successive higher centers, up to & including primary auditory cortex

34 Tonotopic organization of primary auditory cortex Source: Lynch, downloaded

35 © 2011 Pearson Education, Inc. Localizing sounds Most auditory information crosses over but some doesn’t, so brainstem and cortical areas get inputs from both ears Right versus left arrival time difference Right versus left intensity difference Both are used to localize sounds

36 © 2011 Pearson Education, Inc. Conduction deafness Sound energy is not conducted from outside world to the receptors, i.e. doesn’t make it to inner ear Causes include: Water or excess cerumen in external ear Scarring or perforation of tympanic membrane Immobility of ear ossicles (fluid, pus, tumor; otosclerosis) Otosclerosis: abnormal bony growth around stapes footplate prevents normal stapes movement.

37 © 2011 Pearson Education, Inc. Sensorineural (nerve) deafness Most common cause of permanent deafness Damage to hair cell receptors Normal (young) range: 20–20,000 Hz; hearing loss later, high frequencies go first Loud noise, infection, some drugs Damage to nerve or to central auditory pathways

38 © 2011 Pearson Education, Inc. Normal organ of Corti, with tectorial membrane removed to show hair cells. Ryan AF. Protection of auditory receptors and neurons: evidence for interactive damage. PNAS 97: , ©2000 by National Academy of Sciences Damaged organ of Corti. Hair cells in healthy and damaged cochleas

39 © 2013 Pearson Education, Inc. Treating 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


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