Passage Four
If we had to rely on only five senses for survival, we would be in very sad shape indeed. We wouldn’t know up from down. We wouldn’t know when to eat or drink. We wouldn’t know what our muscles were doing or what position our limbs were in. We wouldn’t know when our body was damaged, because we wouldn’t feel pain. We might freeze to death without even a shake, or overheat without a drop of sweat. The five senses--touch, taste, smell, hearing and sight--respond only to stimulation from the out- side world, but the inside world of our bodies must also receive and respond to important messages.
Our internal senses keep us alive and enable us to use our external senses. In effect, the internal senses tell our brains how to run our bodies. Hunger and thirst register in a part of the brain called the hypothalamus, when a lack of food chemicals are detected in the blood.
Another internal sense that controls our ba
A. too much food and water in the body
B. a lack of oxygen in the blood
C. seeing or thinking about food
D. a lack of certain chemicals in the blood
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