Communication between cells is key to organism-level regulation of the internal

Intercellular communication occurs largely through the nervous system and the endocrine system. In general, the nervous system performs short-term "crisis management," whereas the endocrine system regulates longer-term, ongoing metabolic processes. Ideally, the nervous system communicates by an impulse over an axon to a neuron or some other effector. This is a very fast and spatially specific process. In contrast, the endocrine system relies on blindly sending out chemical messages to the whole body through the blood and interstitial fluid. This process is slow, and relies on the response of a different target cell.

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