Nervous System III
Motion sickness is a disturbance of the inner ear’s sensation of bal-
ance. Nine out of ten people have experienced this nausea and vom-
iting, usually when riding in a car or on a boat. Astronauts suffer a
form of motion sickness called space adaptation syndrome.
Motion sickness is thought to result when visual information
contradicts the inner ear’s sensation that one is motionless. Consider
a woman riding in a car. Her inner ears tell her that she is not moving,
but the passing scenery tells her eyes that she is moving. The problem
is compounded if she tries to read. The brain reacts to these seem-
ingly contradictory sensations by signaling a “vomiting center” in the
Distinguish between the senses of static and dynamic equilibrium.
Which structures provide the sense of static equilibrium? Of
How does sensory information from other receptors help
Sensory nerve fiber
hair cells bend
Scanning electron micrograph of hairs of hair cells,
such as those in the utricle and saccule (8,000×).
(a) Head upright
(b) Head bent forward
The maculae respond to changes in head position. (
) Macula of the utricle with the head in an upright position. (
) Macula of the
utricle with the head bent forward.