Action Potential

Neurons get an electrical imbalance, with a relative positive charge outside and negative charge inside. This comes about as the membrane surrounding the neuron lets out three Sodium ions(Na+) and brings in two Potassium ions(K+); this is called the Sodium Pump. The net effect is to have a relatively positive charge outside the cell. As the electrical charge builds outside the cell, the voltage difference will rapidly increase. Eventually this imbalance triggers channels in the membrane to open that will release the Potassium that is built up inside and the process starts anew.

This imbalance, called action potential, happens at just one small spot on the neuron. when the change occurs, there will be an electrical imbalance to the area just next to it. In this way, electrons essentially pulse down the neuron. These pulses travel much faster if the diameter is larger. Squid have the largest diameter, and so the fastest pulses. The problem with larger diameters however is that the signal fades out faster, so they can't travel long distances. They are also easier to see and as a result a lot of experiments have been done on our multi-legged friends. The other thing that increases speed is myelin sheaths. These sheaths have breaks in them, that have the poetic name of the 'nodes of ranvier'. Myelin essentially prevents the positive imbalance everywhere but the gaps, this forces the electrons to shoot from node to node, speeding the transfer.