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The brain is the body’s command center: It receives sensory information from the eyes, ears, nose, tongue, skin, and internal organs, and sends instructions to the rest of the body. Up to this point, we have examined how individual neurons send signals to other nerve and muscle cells. How are these neurons organized in the body to sense stimuli, process them, and issue an appropriate response? How does the brain coordinate the movement of limbs necessary to walk or run, and adjust heart rate and breathing in response to exercise? In this section, we look at how the nervous system is organized to allow the brain and the body to communicate with each other.