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.
An action potential, which is the nerve impulse, occurs when a threshold is reached. Upon stimulation, the sodium gates open, Na+ flows into the axon, and the action potential swings up from -65mV to +40 mV.. The axon of a neuron conducts nerve impulses away from the cell body. Neurons that conduct messages from a sense organ to the central nervous system are called sensory, or afferent neurons. Those neurons that conduct an impulse from the CNS to a muscle or gland are called. motor, or efferent, neurons.