Investigating nerve impulses

Nerves convey information rapidly from one part of the body to another, enabling animals to respond quickly to changes in their external and internal environments. The information is carried in the form of electrical signals called nerve impulses.Most of our understanding of the nature of nerve impulses comes from work done on giant axons of squids. These are the nerve fibres responsible for the rapid escape movements of squids. Their large diameter (up to 1 mm) makes it possible to measure the electrical activity in a giant axon when it is at rest and when it is conveying a nerve impulse.

A fine glass microelectrode is inserted inside an axon, and the voltage (potential difference; p.d.) between it and a reference electrode on the surface of the axon can be displayed on a cathode ray oscilloscope. By convention, the potential difference of the inside of the cell is always measured relative to that on the outside, so that the outside potential is taken as zero.