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.
Any of the impulse-conducting cells that constitute the brain, spinal column, and nerves in vertebrates, consisting of a nucleated cell body with one or more dendrites and a single axon. 2. A similar impulse-conducting cell in invertebrates. In both senses also called nerve cell.