The sudden movement of an individual in response to an unexpected visual
stimulus is part of the startle reflex.
Changes in the size of the pupil with changes in the amount of light are produced
by the pupillary reflex.
Automatic movement of the eyelids over the exterior surface of the eyeball is
The lacrimal fluid keeps the conjunctiva transparent. Also, with the blink reflex,
the lacrimal fluid washes away foreign particles.
The secretion of the special oil glands of the upper and lower eyelids helps
prevent the lacrimal fluid from escaping.
The auricle serves as a collector of airborne waves. At the inner end of the
external auditory meatus, the waves act upon the tympanic membrane.
The tympanic membrane separates the external ear from the middle ear. The
tympanic membrane mechanically oscillates in response to airborne waves from
The air of the middle ear cavity is continuous with the air of the surrounding
environment, due to the auditory tube. The auditory tube serves to equalize the
air pressures on the two sides of the tympanic membrane. Extreme pressure
differences cause severe pain. The passage of the auditory tube into the
nasopharynx opens when one swallows.
Mechanical oscillations are transmitted from the tympanic membrane to the oval
window by way of the auditory ossicles. The intensity of these mechanical
oscillations is somewhat controlled by the auditory muscles. (para 13-12)
The mechanical, plunger-like actions of the stapes impart pressure pulses to the
The basilar membrane is made up of transverse fibers. Acting like the strings of
an instrument, the individual fibers mechanically vibrate in response to specific
frequencies of pulses in the perilymph.
When the basilar membrane vibrates, the hair cells of the organ of Corti are
mechanically deformed so that the associated neuron is stimulated. (para 13-13)