Beginning from All or Nothing- How, then, does one perceive the intensity of a stimulus?

1. The number of times a neuron fires per unit time (per second). Two different lag times: charges and reset time.
2. The number of neurons firing. Greater number of neurons firing means greater intensity.

IV. The Synapse - Junctions between neurons. 2 types of synapses:

1. Mechanical synapses - axon abuts the dendrite. Automatic transfer of electricity. 
2. Chemical synapse- axon doesn't abut the dendrite. Message goes from electrical to chemical and then back to electrical. All of our synapses are chemical. 

There are 2 "events"  that can happen at the synapse:
A. Excitation-when the pre-synaptic neuron releases an excitatory neurotransmitter to cause the post-synaptic neuron to be more likely to "fire."