chapter 7 notes

chapter 7 notes - CHAPTER 7: Audition and somatosenses A....

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CHAPTER 7: Audition and somatosenses A. Audition The stimulus: when an object vibrates, air molecules surrounding it alternately condense and rarefy, producing waves that travel away from the object at approx. 700 mph. human ear receptor cells can be stimulated by vibrations ranging between 30 and 20,000 times a second. Sound has 3 perceptual dimensions which correspond to 3 physical dimensions: physical: amplitude (intensity) → perceptual: loudness physical: frequency → perceptual: pitch (measured in cycles/sec, or hertz, Hz) physical: complexity → perceptual: timbre The eye is synthetic; the ear is analytical → when two different frequencies of sound waves are mixed, we do not perceive them as one sound; we hear both original tones. This gives us the capacity to identify the nature of particular sounds. Anatomy: outer ear: pinna (external ear) ear canal tympanic membrane (eardrum) middle ear: a hollow region behind the tympanic membrane contains the ossicles: the malleus (hammer) connects with the tympanic membrane and transmits vibrations via the incus (anvil) and stapes (stirrup) to the cochlea. inner ear: Oval window: opening in the bony process surrounding the cochlea; reveals the membrane, so that vibrations from the stapes may be transmitted into the cochlear fluid. cochlea: structure that contains the receptors. 2 ¾ turns of a gradually tapering cylinder; 35 mm long. Separated longitudinally into 3 sections: scala vestibula, media, tympani. organ of Corti: the receptive organ → consists of the basilar membrane, the hair cells, and the tectorial membrane. Hair cells: the auditory receptors. They are anchored to the basilar membrane by rodlike Deiter's cells (a kind of supporting cell). The cilia of the hair cells pass through the reticular membrane, and the ends of some of them attach to the fairly rigid tectorial membrane, which projects overhead. How are receptor potentials produced? Sound waves cause the basilar membrane to move relative to the tectorial membrane, which bends the cilia of the hair cells. round window: another membrane-covered opening that allows the fluid inside the cochlea to move back and forth (complementary to the movements of the oval window).
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Georg von Bekesy: found that the vibratory energy exerted on the oval window causes the basilar membrane to bend. The portion that bends the most is determined by the frequency of the sound: high-frequency sounds cause the end nearest the oval window to bend. fenestration is a surgical procedure in which a tiny hole is drilled into the bone where the round window should be, so that their basilar membrane can more easily flex back and forth. Transduction of Auditory Information:
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chapter 7 notes - CHAPTER 7: Audition and somatosenses A....

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