Question

What is action potential? Describe how the nerve impulse is propagated in a non-myelinated and myelinated nerve fibre.

Answer 1

• The action potential is defined as a change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or a nerve cell.
  
• Myelinated fibres are those that possess myelin sheath on the axon. There are gaps between the myelin sheath known as node of Ranvier. The myelin sheath acts as the electrical insulator and provides the resistance in the passage of the nerve impulses. Since there is no sheath at the node of Ranvier it helps in the conduction of the nerve impulse. Thus, when nerve impulse travels down, it appears that they jump from one node to another. Such type of conduction is known as saltatory conduction.
  
• The basic principle of origin and propagation of the nerve impulse is the same in the non-myelinated sheath as well. Since the myelin sheath is absent in these fibres the nerve impulse travels through the entire axon body. Thus, the speed of conduction in myelinated fibres is much greater than the non-myelinated fibres.