The squirrel body is relied only on electrical impulses via nerve cells, the range of tissues instructed to prepare for the coming activity would be limited. On the other hand, if a chemical signal were to be sent as well, it would reach all cells of the body and provide the wide range of changes needed. This is done using a hormone called adrenaline that is secreted from the adrenal glands.
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Chemical coordination is better than electrical impulsesasameans of communication between the cells in a multi-cellular organism because in animals, the messages are communicated in the form of nerve impulses quickly. But still, there are some limitations to the nervous system. Nerve impulses can reach only those cells which are connected by the nervous tissues and the cells connected by nervous tissues, after generation and transmission of the impulse, take some time to rest before the generation and transmission of new impulse. In simple words, cells cannot continuously generate and transmit nerve impulses. This is the reason why most multicellular organisms use another form of control and coordination, named chemical coordination. The advantage of chemical coordination is that the information spreads out throughout the body by blood (then the required part picks it up as per its requirement) and the effect generally lasts longer.