1. Fill in the blanks.

Chemical messengers called (1) ___
attach to receptor sites on the
(2) ____ of the receiving neuron. When enough of those excitatory chemical messengers are attached, the neuron reaches the point of firing called (3) _____.
Neurons either fire or they don't. There is no "sort of" firing. This is called an (4) _____ response. The firing is called a neural impulse - also called an (5) ______.
The neural impulse travels down the length of the (6) ____ to the
distant ends of the neuron called the (7) ____. This causes the chemical
messengers to be released into the empty spaces between neurons called the (8) _____ where they float across to the receptor sites on the receiving neuron, and the whole process repeats.