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 Area of high pressure (compressed molecules) Crest Trough Distance Amplitude Area of low 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. Wavelength Air pressure

Copyright © 2010 Pearson Education, Inc. Properties of Sound Waves Frequency Number of waves over a given time Wavelength Distance between crests Amplitude Height

Copyright © 2010 Pearson Education, Inc. 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 Time (s) (a) Frequency is perceived as pitch. High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch (b) Amplitude (size or intensity) is perceived as loudness. High amplitude = loud Low amplitude = soft Time (s) Pressure

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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 Basilar membrane 1 Sound waves vibrate the tympanic membrane. 2 Auditory ossicles vibrate. Pressure is amplified. 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. MalleusIncus Auditory ossicles Stapes Oval window Scala vestibuli Helicotrema Cochlear nerve Round window Tympanic membrane (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 displace the basilar membrane near the middle. Low-frequency sounds displace the basilar membrane near the apex. Base (short, stiff fibers) Frequency (Hz) Apex (long, floppy fibers) Basilar membrane High-frequency sounds displace the basilar membrane near the base.

Copyright © 2010 Pearson Education, Inc. 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 nerve fibers Basilar membrane Fibers of cochlear nerve Supporting cells

Copyright © 2010 Pearson Education, Inc. 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 Ca 2+ current causes release of neurotransmitter glutamate Cochlear fibers transmit impulses to brain

Copyright © 2010 Pearson Education, Inc. Figure Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior 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

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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 CaCO 3 stones)

Copyright © 2010 Pearson Education, Inc. Figure Macula of saccule Otoliths Hair bundle Kinocilium Stereocilia Otolithic membrane Vestibular nerve fibers Hair cells Supporting cells Macula of utricle

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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 Otolithic membrane Kinocilium Stereocilia Receptor potential Nerve impulses generated in vestibular fiber When hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials. When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency. Depolarization Hyperpolarization

Copyright © 2010 Pearson Education, Inc. 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 (kinocilium plus stereocilia) Hair cell Supporting cell Membranous labyrinth Crista ampullaris Crista ampullaris Endolymph Cupula (a) Anatomy of a crista ampullaris in a semicircular canal (b) Scanning electron micrograph of a crista ampullaris (200x)

Copyright © 2010 Pearson Education, Inc. 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 Cerebellum Oculomotor control (cranial nerve nuclei III, IV, VI) (eye movements) Spinal motor control (cranial nerve XI nuclei and vestibulospinal tracts) (neck movements) Visual receptors Somatic receptors (from skin, muscle and joints) Vestibular nuclei (in brain stem) 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. Output: Fast reflexive control of the muscles serving the eye and neck, limb, and trunk are provided by the outputs of the central nervous system. Vestibular receptors Central nervous system processing