The chemicals in the brain that send messages from one nerve ending to
another are called:

These chemicals are called neurotransmitters, and the process is called neurotransmission. The space between the axon and the dendrites is called the synapse. When neurons communicate, an electrical impulse triggers the release of neurotransmitters from the axon into the synapse.

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the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.

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