Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
A nerve impulse begins when a neuron receives a chemical stimulus. The impulse travels down the axon membrane as an electrical action potential to the axon terminal. The axon terminal releases neurotransmitters that carry the nerve impulse to the next cell.


Question: What begins when a neuron receives a chemical stimulus?
a nerve impulse
A nerve impulse begins.