(a) The receptor organ is the ear (membranous labyrinth).
The stimulus is gravitational forces.
Located in the upper recesses of the nasal chambers is a special layer of tissue
called olfactory epithelium. Within the olfactory epithelium are special hair cells
(chemoreceptors) that react to airborne molecules. Information received by the hair
cells is transmitted from the olfactory nerves to the olfactory bulbs and along the
olfactory tract to the brain, where it is interpreted as the sensation of smell.
Located on the tongue and back of the mouth are sensory receptors called taste
buds. Special hair cells in the taste buds are chemoreceptors that react to molecules of
material taken into the mouth (food, liquids, and so forth.). Information received by the
hair cells is transmitted to the brain, where it is interpreted as the sense of taste.
The eye (figure 1-1) is the special sense organ responsible for vision. Rays of
light (reflected from an object) pass through the cornea, aqueous humor, pupil, lens,
and vitreous humor to stimulate the receptor tissue (rods and cones) in the retina. The
resulting nerve impulses travel to the brain, where they are interpreted as sight.
The human ear (figure 1-2) serves two major sensory functions--hearing and
a. Sound stimuli travel as airborne waves, which are collected by the external
ear. The airborne waves pass through the external auditory meatus (ear canal) to the
tympanic membrane, which separates the external and middle ear.
b. The physical vibration of the airborne waves is converted to mechanical
vibration by the tympanic membrane and the ossicles. The ossicles (malleus, incus,
and stapes) articulate with both the tympanic membrane and the oval window, which
opens into the vestibule of the inner ear.
c. When the ossicles are set into mechanical vibration, the stapes acts as a
plunger against the oval window, imparting pressure pulses to the fluid (perilymph) of
the inner ear.