Touch
When you look at the prickly cactus inFigure20.28, does the wordouchcome to mind?
Touching the cactus would no doubt be painful. Touchis the sense of pain, pressure, or
temperature. It depends on sensory neurons in the skin. The skin on the palms of the hands,
soles of the feet, and face has the most sensory neurons and is especially sensitive to touch.
The tongue and lips are very sensitive to touch, as well. Neurons that sense pain are also
found inside the body in muscles, joints, and organs. If you have a stomach ache or pain
from a sprained ankle, it’s because of these internal sensory neurons.
Figure 20.28: The spines on this cactus are like needles, they help keep away animals that
might want to eat the cactus. ( 18 )
The following example shows how messages about touch travel from sensory neurons to the
brain, as well as how the brain responds to the messages. Suppose you wanted to test the