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After studying this chapter, you should be able to:

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  • Describe the components and functions of the external, middle, and inner ear.
  • Describe the way that movements of molecules in the air are converted into impulses generated in hair cells in the cochlea.
  • Explain the roles of the tympanic membrane, the auditory ossicles (malleus, incus, and stapes), and scala vestibule in sound transmission.
  • Explain how auditory impulses travel from the cochlear hair cells to the auditory cortex
  • Explain how pitch, loudness, and timbre are coded in the auditory pathways.
  • Describe the various forms of deafness and the tests used to distinguish between them.
  • Explain how the receptors in the semicircular canals detect rotational acceleration and how the receptors in the saccule and utricle detect linear acceleration.
  • List the major sensory inputs that provide the information that is synthesized in the brain into the sense of position in space.

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Our ears not only let us detect sounds, but they also help us maintain balance. Receptors for two sensory modalities (hearing and equilibrium) are housed in the ear. The external ear, the middle ear, and the cochlea of the inner ear are concerned with hearing. The semicircular canals, the utricle, and the saccule of the inner ear are concerned with equilibrium. Both hearing and equilibrium rely on a very specialized type of receptor called a hair cell. There are six groups of hair cells in each inner ear: one in each of the three semicircular canals, one in the utricle, one in the saccule, and one in the cochlea. Receptors in the semicircular canals detect rotational acceleration, receptors in the utricle detect linear acceleration in the horizontal direction, and receptors in the saccule detect linear acceleration in the vertical direction.

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External & Middle Ear

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The external ear funnels sound waves to the external auditory meatus (Figure 10–1). In some animals, the ears can be moved like radar antennas to seek out sound. From the external auditory meatus, sound waves pass inward to the tympanic membrane (eardrum).

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Figure 10–1
Graphic Jump Location

The structures of the external, middle, and inner portions of the human ear. Sound waves travel from the external ear to the tympanic membrane via the external auditory meatus. The middle ear is an air-filled cavity in the temporal bone; it contains the auditory ossicles. The inner ear is comprised of the bony and membranous labyrinths. To make the relationships clear, the cochlea has been turned slightly and the middle ear muscles have been omitted. (From Fox SI, Human Physiology. McGraw-Hill, 2008.)

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The middle ear is an air-filled cavity in the temporal bone that opens via the eustachian (auditory) tube into the nasopharynx and through the nasopharynx to the exterior. The tube is usually closed, but during swallowing, chewing, and yawning it opens, keeping the air pressure on ...

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