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Properties of Sound
• Sound
• A pressure disturbance (alternating high and low pressure) produced by a vibrating object
• Sound wave
• Moves outward in all directions
• Is illustrated as an S-shaped curve or sine wave
Copyright © 2010 Pearson Education, Inc. Figure 15.29
Area ofhigh pressure(compressedmolecules)
Crest
Trough
Distance Amplitude
Area oflow pressure(rarefaction)
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.
WavelengthA
ir p
ress
ure
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Properties of Sound Waves
• Frequency
• Number of waves over a given time
•Wavelength
• Distance between crests
• Amplitude
• Height
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Properties of Sound
• Pitch
• Perception of different frequencies
• Normal range is 20–20,000 Hz
• Higher the frequency, higher the pitch
• Loudness
• Subjective interpretation of sound intensity
• Normal range is 0–120 decibels (dB)
Copyright © 2010 Pearson Education, Inc. Figure 15.30
Time (s)(a) Frequency is perceived as pitch.
High frequency (short wavelength) = high pitchLow frequency (long wavelength) = low pitch
(b) Amplitude (size or intensity) is perceived as loudness.
High amplitude = loudLow amplitude = soft
Time (s)
Pre
ssure
Pre
ssure
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Transmission of Sound to the Internal Ear
• Sound waves vibrate tympanic membrane
• Ossicles vibrate and amplify pressure at oval window
• Pressure waves move through perilymph of scala vestibuli
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Transmission of Sound to the Internal Ear
• Freq below threshold of hearing travel through helicotrema and scali tympani to round window
• Sounds in hearing range go through cochlear duct, vibrating the basilar membrane at a specific location, according to frequency of sound
Copyright © 2010 Pearson Education, Inc. Figure 15.31a
Scala tympani
Cochlear duct
Basilarmembrane
1 Sound waves vibratethe tympanic membrane. 2 Auditory ossicles vibrate.
Pressure is amplified.
3 Pressure waves created bythe stapes pushing on the oval window move through fluid in the scala vestibuli.
Sounds with frequenciesbelow 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.
Malleus Incus
Auditory ossicles
Stapes
Ovalwindow
Scala vestibuli
Helicotrema
Cochlear nerve
32
1
Roundwindow
Tympanicmembrane
(a) Route of sound waves through the ear
Copyright © 2010 Pearson Education, Inc. Figure 15.31b
Fibers of basilar membrane
(b) Different sound frequencies cross the basilar membrane at different locations.
Medium-frequency sounds displacethe basilar membrane near the middle.
Low-frequency sounds displace thebasilar membrane near the apex.
Base(short,stifffibers)
Frequency (Hz)
Apex(long,floppyfibers)
Basilar membrane
High-frequency sounds displacethe basilar membrane near the base.
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Excitation of Hair Cells in the Spiral Organ
• Cells of spiral organ
• Afferent fibers of cochlear nerve coil about the bases of hair cells
Copyright © 2010 Pearson Education, Inc. Figure 15.28c
(c)
Tectorial membrane Inner hair cell
Outer hair cells
Hairs (stereocilia) Afferent nervefibers
Basilarmembrane
Fibers ofcochlearnerve
Supporting cells
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Excitation of Hair Cells in the Spiral Organ
• Stereocilia
• Protrude into endolymph
• Enmeshed in gel-like tectorial membrane
• Bending stereocilia
• Opens mechanically gated ion channels
• Inward K+ and Ca2+ current causes release of neurotransmitter glutamate
• Cochlear fibers transmit impulses to brain
Copyright © 2010 Pearson Education, Inc. Figure 15.33
Medial geniculatenucleus of thalamus
Primary auditorycortex in temporal lobeInferior colliculus
Lateral lemniscus
Superior olivary nucleus(pons-medulla junction)
Spiral organ (of Corti)
Bipolar cell
Spiral ganglion of cochlear nerve
Vestibulocochlear nerve
Medulla
Midbrain
Cochlear nuclei
Vibrations
Vibrations
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Auditory Processing
• Impulses from specific hair cells are interpreted as specific pitches
• Loudness is detected by increased numbers of action potentials
• Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears
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Homeostatic Imbalances of Hearing
• Conduction deafness
• Blocked sound conduction to fluids of internal ear
• Can result from impacted earwax, perforated eardrum, or otosclerosis of ossicles
• Sensorineural deafness
• Damage to neural structures at any point from the cochlear hair cells to auditory cortical cells
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Homeostatic Imbalances of Hearing
• Tinnitus: sound in ears in absence of auditory stimuli
• Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin
• Meniere’s syndrome: labyrinth disorder that affects the cochlea and semicircular canals
• Causes vertigo, nausea, and vomiting
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Equilibrium and Orientation
• Vestibular apparatus consists of equilibrium receptors in semicircular canals and vestibule
• Vestibular receptors monitor static equilibrium
• Semicircular canal receptors monitor dynamic equilibrium
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Maculae
• Sensory receptors for static equilibrium
• Monitor position of head in space, necessary for control of posture
• Respond to linear acceleration forces, but not rotation
• Stereocilia and kinocilia are embedded in otolithic membrane studded with otoliths (tiny CaCO3 stones)
Copyright © 2010 Pearson Education, Inc. Figure 15.34
Macula ofsaccule
Otoliths
Hair bundle
Kinocilium
StereociliaOtolithicmembrane
Vestibularnerve fibers
Hair cells
Supportingcells
Macula ofutricle
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Activating Maculae Receptors
• Bending of hairs in direction of kinocilia
• Depolarizes hair cells
• Increases the amount of neurotransmitter release and increases the frequency of action potentials generated in vestibular nerve
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Activating Maculae Receptors
• Bending in opposite direction
• Hyperpolarizes vestibular nerve fibers
• Reduces the rate of impulse generation
• Thus the brain is informed of the changing position of the head
Copyright © 2010 Pearson Education, Inc. Figure 15.35
Otolithic membrane
Kinocilium
Stereocilia
ReceptorpotentialNerve impulsesgenerated investibular fiber
When hairs bend towardthe kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials.
When hairs bend awayfrom the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency.
DepolarizationHyperpolarization
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Crista Ampullaris (Crista)
• Sensory receptor for dynamic equilibrium
• One in each semicircular canal
• Major stimuli are rotatory movements
Copyright © 2010 Pearson Education, Inc. Figure 15.36a–b
Fibers of vestibular nerve
Hair bundle (kinociliumplus stereocilia)
Hair cell
Supportingcell
Membranouslabyrinth
Cristaampullaris
Cristaampullaris
Endolymph
Cupula
Cupula
(a) Anatomy of a crista ampullaris in a semicircular canal
(b) Scanning electron micrograph of a crista ampullaris (200x)
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Equilibrium Pathway to the Brain
• Pathways are complex and poorly traced
• Impulses travel to vestibular nuclei in brain stem or the cerebellum, both of which receive other input
• Three modes of input for balance and orientation
• Vestibular receptors
• Visual receptors
• Somatic receptors
Copyright © 2010 Pearson Education, Inc. Figure 15.37
Cerebellum
Oculomotor control(cranial nerve nuclei
III, IV, VI)
(eye movements)
Spinal motor control(cranial nerve XI nuclei
and vestibulospinal tracts)
(neck movements)
Visualreceptors
Somatic receptors(from skin, muscle
and joints)
Vestibularnuclei
(in brain stem)
Input: Information about the body’s position in space comesfrom three main sources and is fed into two major processingareas in the central nervous system.
Output: Fast reflexive control of the muscles serving the eyeand neck, limb, and trunk are provided by the outputs of thecentral nervous system.
Vestibularreceptors
Central nervoussystem processing