the microscopic "contacts" between nerve cells that allow information to be passed from one cell to the next; for each synapse, a thin gap exists between the end of one axon and the surface of the neuron receiving the input; electrical impulses cannot "jump" across this gap, thus chemicals (or neurotransmitters) are used to cross the synapse and stimulate the recipient neuron; synapses can be either "excitatory" or "inhibitory", and stimulate or turn off the recipient neuron, respectively.