Learning What Nerve Cells Do
When neurons are active, as they almost always are even when you sleep, they do two things:
A famous experiment by Luigi Galvani in the late 1700s showed that electricity was involved in the nervous system. He showed, for example:
These observations suggested that electricity is used in the body to send messages. It was soon observed that the messages were carried in yellow cords that connected muscles to the spinal cord. Next time you eat a chicken leg, look at the long yellow cord that lies near the major blood vessels of the leg - it is a nerve!
Ever see a mechanic put a voltmeter on the battery in the family car? Meters like this register any flow of electric current. The electricity in a nerve involves such a small amount of current that it has to be amplified and displayed by a TV-like instrument called an oscilloscope. A complete electrical circuit is made by touching a nerve with a metal probe that connects to the oscilloscope that also has a return probe back to the animal. Then, as pulses of electricity are generated in the nerve, they will be detected by the oscilloscope, which generates a light beam that changes with each pulse from the nerve. Instruments like this prove that nerves generate electrical pulses and can be used to study what the pulses look like and the number of pulses over time under various conditions.