nervous system. Human beings have several senses. They include sight, hearing, balance,
touch, taste, and smell. We have special sense organs for each of these senses. Sensory
neurons in each sense organ detect a certain type of stimulus, or input. For example, sensory
neurons in the eyes detect light, and sensory neurons in the skin detect touch.
Other animals have senses that humans don’t have. For example, sharks and some other
fish can detect weak electric currents. Many animals can detect magnetism. Detecting
magnetism is like having an internal compass. It helps the animals find their way from
place to place. For example, birds use their sense of magnetism to guide their seasonal
migrations.Our sense organs detect sensations, but they don’t tell us what we are sensing. For example,
when you inhale chemicals given off by baking cookies, your nose doesn’t tell you that you
are smelling cookies. That’s your brain’s job. The sense organs send messages about sights,
smells, and other stimuli to the brain (Figure20.8). The brain then interprets the messages.
A particular area of the brain interprets information from each sense organ (Figure20.5).
For example, information from the nose is interpreted by the temporal lobe of the cerebrum.
Figure 20.8: Remember which lobes of the cerebrum interpret messages from each of the
senses; decide which senses would be stimulated by these raspberries or look back atTable
(20.1) for clues. ( 28 )
Themotor divisionof the peripheral system carries messages from the central nervous
system to internal organs and muscles. As shown inFigure20.7, the motor division is also
divided into two parts: the somatic nervous system and the autonomic nervous system. The
somatic nervous systemcarries messages that control body movements. It’s responsible
for activities that are under your control, such as waving your hand or kicking a ball. The