One more thing. All these things -- the sending of messages, etc -- occurs because electrical signals are produced by chemical reactions. Ions are necessary for these to occur.
A nerve impulse is the relaying of a coded signal from a nerve cell to an effector (a muscle cell, a gland cell or another nerve cell) in response to a stimulus. It is the means by which a nerve cell communicates with another cell. This signal is relayed along the axon of the nerve cell, bringing a message that instructs an effector to act. For instance, in neuromuscular junction, the nerve impulse moves along the axon of a nerve cell to instruct a muscle cell to contract.