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Module 1.6c


                         The Ear

                                    1.6-10         How does the ear transform sound energy into neural messages?
                                    1.6-10   How does the ear transform sound energy into neural messages?
                        How does vibrating air trigger nerve impulses that your brain can decode as sounds? The
                      process begins when sound waves strike your  eardrum,  causing this tight membrane to         middle ear       the chamber


                      vibrate (  Figure 1.6-18 ).                                                       between the eardrum and the
                                                                                                        cochlea containing three tiny


                            In your   middle ear  a piston made of three tiny bones — the  hammer (malleus),  anvil  bones that concentrate the

                                           ,
                      (incus), and  stirrup  (stapes) — picks up the vibrations and transmits them to the   cochlea ,        vibrations of the eardrum on the


                      a snail-shaped tube in your   inner ear .                                         cochlea’s oval window.
                                    The incoming vibrations then cause the cochlea’s membrane-covered opening (the  oval      cochlea      [KOHK-lee-uh] a
                      window ) to vibrate, jostling the fluid inside the cochlea. This motion causes ripples in the  basilar   coiled, bony, fluid-filled tube
                      membrane,  bending the  hair cells  lining its surface, rather like grass blades bending in the wind.   in the inner ear; sound waves
                            The hair cell movements in turn trigger impulses in the adjacent nerve cells, whose axons   traveling through the cochlear
                                                                                                        fluid trigger nerve impulses.


                      converge to form the  auditory nerve. The auditory nerve carries the neural messages to your
                                           Copyright © Bedford, Freeman & Worth Publishers.
                      thalamus and then on to the  auditory cortex  in your brain’s temporal lobe .  From vibrating air,      inner ear       the innermost
                                                                                                        part of the ear, containing the
                      to tiny moving bones, to fluid waves, to electrical impulses to the brain: Voila! You hear!   cochlea, semicircular canals, and
                                                                                                        vestibular sacs.
                         (a)       OUTER EAR        MIDDLE EAR  INNER EAR
                                                         Semicircular canals
                                                Bones of the
                                                middle ear         Bone
                                                                        Auditory nerve
                          Sound  Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
                          waves                                             Cochlea



                                                   Eardrum
                          Auditory                                Oval window
                          canal                                   (where stirrup attaches)

                                                            Hammer   Anvil        Cochlea,             Auditory cortex
                                                            (malleus)  (incus)    partially uncoiled   of temporal lobe


                         (b)
                               Enlargement of middle ear
                               and inner ear, showing                                                   Auditory nerve
                               cochlea partially uncoiled   Sound
                               for clarity             waves                                         Nerve fibers to auditory nerve
                                                                                               Protruding hair cells
                                                                                               Basilar membrane
                                                               Eardrum  Stirrup             Motion of fluid in the cochlea
                                                                       (stapes)  Oval window


                                  Figure   1.6-18
                          Hear here: How we transform sound waves into nerve impulses that our brain interprets
                        (a) The outer ear funnels sound waves to the eardrum. The bones of the middle ear amplify and relay the eardrum’s vibrations through the
                        oval window into the fluid-filled cochlea. (b) As shown in this detail of the middle ear and inner ear, the cochlear fluid’s resulting pressure
                        changes cause the basilar membrane to ripple, bending the hair cells on its surface. Hair cell movements trigger impulses at the nerve cells’
                        base, whose fibers converge to form the auditory nerve. That nerve sends neural messages to the thalamus and on to the auditory cortex.



                                                                                            Sensation: Hearing  Module 1.6c   137






          03_myersAPpsychology4e_28116_ch01_002_163.indd   137                                                                  15/12/23   9:26 AM
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