The Human Brain : From Neurone to Nervous System
NERVE CELLS : THE ACTION POTENTIAL
- Neurones are specialised cells that communicate with each other and other electrically excitable tissues, often over long distances, by passing impulses (action potentials) very rapidly along their axonal membranes.
Neurones provide a rapid means of communication over long distances within the body by passing action potentials - nerve impulses - along their axonal membranes.
Action potentials are transient changes in potential across the axonal membrane, which are conducted at spectacularly fast speeds (over 100m/sec) because of the myelin formed by Schwann cells or Oligodendrocytes. The Nodes of Ranvier are the small areas of nerve membrane between adjacent areas of myelin.
- Saltatory conduction is the process whereby the action potential jumps from one Node of Ranvier to the next.
Myelinated axons have larger diameters, lower thresholds and higher conduction velocities than unmyelinated axons; the speed of conduction of the impulse is directly related to the degree of myelination (because the action potential jumps form node to node).
Key Words: Action potential, 'Spike', voltage gated sodium channels, voltage gated potassium channels, saltatory conduction, myelin, the relation between conduction velocity and axon diameter