The ways in which the words can be meaningfully combined is defined by the language's syntax and grammar. The actual meaning of words and combinations of words is defined by the language's semantics.
A nerve impulse is an electrical signal that travels along an axon. There is an electrical difference between the inside of the axon and its surroundings, like a tiny battery. When the nerve is activated, there is a sudden change in the voltage across the wall of the axon, caused by the movement of ions in and out of the neuron.
Noun. 1. action potential-the local voltage change across the cell wall as a nerve impulse is transmitted. nerve impulse, nervous impulse, neural impulse, impulse-the electrical discharge that travels along a nerve fiber; they demonstrated the transmission of impulses from the cortex to the hypothalamus. 1  Facebook. 2  Twitter.