Figure 1-7. Diagram of the scalae.
a. Sensation of Sound. If a medium is set into vibration within certain
frequency limits (average between 25 cycles per second and 18,000 cycles per
second), we have a sound stimulus. The sensation of sound occurs only when these
vibrations are interpreted by the cerebral cortex of the brain at the conscious level. The
human ear is the special sensory receptor for the sound stimulus. As the stimulus
passes from the external medium (air, water, or a solid conductor of sound) to the actual
receptor cells in the head, the vibrations are in the form of (1) airborne waves, (2)
mechanical oscillations, and (3) fluid-borne pulses.
b. Events in the Physiology of Hearing Sound Waves. The function of
hearing involves many structures and is a complicated process. Here is a brief listing of
the events in the process:
(1) The external ear (the auricle) funnels sound waves into the more internal
structures concerned with hearing. The external auditory meatus directs sound waves
inward, forward, and down to the tympanic membrane.
(2) In the tympanic membrane area, there are ceruminous glands that
secrete ear wax (cerumen). Too much ear wax can partially obstruct the auditory canal
and interfere with hearing.