12. As the stimulus grows stronger, the neuron’s cell body triggers the neuron to initiate an impulse. This impulse is called an ____________. It travels the length of the ___________. As the stimulus become more intense, it will become strong enough to generate an ______________.

13. Some axons are covered by a fatty substance called the ______________. There are small breaks in the _____________. When _____________ reaches one of these breaks, the electrical charge leaps over it. That’s how the ________________ speeds up the transmission of nerve impulses.

14. The synapse is the ______ between two _________. Chemical messengers called ___________ travel from the axon of a sending neuron to the dendrites of a receiving neuron. When action potential reaches the end of one axon, ____________ are released into the gap between the two cells. This may trigger a _________ in the receiving neuron.