Section X. THE SPECIAL SENSE OF HEARING (AUDITORY)
The human ear serves two major special sensory functions--hearing (auditory)
and equilibrium (balance). The stimulus for hearing is sound waves. The stimulus for
a. Methods of Sound Transmission. The sound stimulus is transmitted in a
variety of ways. Regardless of the actual transmission method, the sound stimulus is
unchanged. Sound may be transmitted as:
(1) Airborne waves. These airborne waves have frequency (pitch) and
amplitude (loudness or intensity).
(2) Mechanical oscillations (vibrations) of structures.
(3) Fluid-borne pressure pulses.
(4) Electrical impulses along the neurons to and in the brain.
b. Sections of the Human Ear (figure 11-12). The human ear has three major
parts. Each part serves a specific function in the transmission and reception of the
sound stimulus. The three parts are known as the external (outer) ear, the middle ear,
and the internal (inner) ear.
11-31. THE EXTERNAL EAR
The external ear begins on the outside of the head in the form of a
funnel-shaped auricle (pinna). Actually serving as a funnel, the auricle directs airborne
sound waves into the external auditory meatus. The external auditory meatus is a
tubular canal extending into the temporal portion of the skull.
11-32. THE MIDDLE EAR
a. Tympanic Membrane. At the inner end of the external auditory meatus is
the tympanic membrane. The tympanic membrane (eardrum) is a circular membrane
separating the external auditory meatus from the middle ear cavity. The tympanic
membrane vibrates (mechanically oscillates) in response to airborne sound waves.
b. Middle Ear Cavity. On the medial side of the tympanic membrane is the
middle ear cavity. The middle ear cavity is a space within the temporal bone.