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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.

  • 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.

INTRODUCTION

Specialized receptors (hair cells) for two sensory modalities (hearing and equilibrium) are housed in the ear. The external ear, middle ear, and cochlea of the inner ear are involved with hearing. The semicircular canals, utricle, and saccule of the inner ear are involved with equilibrium. There are six groups of hair cells in each inner ear: one in each of the three semicircular canals, the utricle, the saccule, and the cochlea. Receptors in the semicircular canals detect rotational acceleration, those in the utricle detect linear acceleration in the horizontal direction, and those in the saccule detect linear acceleration in the vertical direction.

STRUCTURE & FUNCTION OF THE EAR

EXTERNAL, MIDDLE, & INNER EAR

Sound travels inward from the external auditory meatus to the tympanic membrane of the external ear or pinna (Figure 10–1). Auditory ossicles (malleus, incus, and stapes) and two small muscles (tensor tympani and stapedius) are located in the middle ear (Figure 10–2). The inner ear (or labyrinth) has three components: the cochlea, three semicircular canals, and the otolith organs with hair cells that respond to sound, head rotation, and changes in gravity and head tilt, respectively (Figure 10–3).

FIGURE 10–1

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 bony and membranous labyrinths. To make the relationships clear, the cochlea has been turned slightly and the middle ear muscles have been omitted. (Reproduced with permission from Fox SI. Human Physiology, 10th ed. New York, NY: McGraw-Hill; 2008.)

FIGURE 10–2

Schematic representation of the auditory ossicles and the way their movement translates movements ...

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