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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Describe the components and functions of the external, middle, and inner ear.

  • Explain the roles of the tympanic membrane, the auditory ossicles (malleus, incus, and stapes), and scala vestibule in sound transmission.

  • Describe the way that movements of molecules in the air are converted into impulses generated in hair cells in the cochlea.

  • Explain how pitch, loudness, and timbre are coded in the auditory pathways.

  • Describe the components of the auditory pathway from the cochlear hair cells to the cerebral cortex.

  • Compare the causes of conductive and sensorineural hearing loss and the tests used to distinguish between them.

  • Define the following terms: tinnitus, presbycusis, and syndromic and nonsyndromic deafness.

  • Explain how cochlear implants and hearing aids function.

  • 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.

  • Describe the neural mechanisms for vestibular nystagmus and how nystagmus can be used as a diagnostic indicator of the integrity of the vestibular system.

  • Describe the cause and clinical signs of the following vestibular disturbances: vertigo, Ménière disease, and motion sickness.

INTRODUCTION

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 involved with hearing. The semicircular canals, the utricle, and the saccule of the inner ear are involved 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, those in the utricle detect linear acceleration in the horizontal direction, and the ones in the saccule detect linear acceleration in the vertical direction.

STRUCTURE & FUNCTION OF THE EAR

EXTERNAL & MIDDLE EAR

The external ear is composed of the auricle (pinna) that captures sound waves, the external auditory meatus (ear canal) through which sound waves travel, and the tympanic membrane (eardrum) that moves in and out in response to sound (Figure 11–1). The tympanic membrane marks the beginning of the middle ear.

FIGURE 11–1

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 composed of the ...

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