Copyright © 2010 Pearson Education, Inc. Properties of Sound Sound A pressure disturbance (alternating high and low pressure) produced by a vibrating object.

Copyright © 2010 Pearson Education, Inc.

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


Properties of Sound Waves

• Frequency

• Number of waves over a given time

•Wavelength

• Distance between crests

• Amplitude

• Height


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)


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


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


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.


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


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


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


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


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


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


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


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)


Macula ofsaccule

Otoliths

Hair bundle

Kinocilium

StereociliaOtolithicmembrane

Vestibularnerve fibers

Hair cells

Supportingcells

Macula ofutricle


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


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


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


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)


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


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

Copyright © 2010 Pearson Education, Inc. Properties of Sound Sound A pressure disturbance (alternating high and low pressure) produced by a vibrating object.

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