The long axons of neurons along with the associated structures are called the nerve fibres. The fibres may be enclosed within sheaths called as myelin sheath. However, the action potential is not generated in the areas where there is a sheath over the fibre. Along the fibres there are regions where the myelin sheath is absent. These regions are called the nodes of Ranvier. The action potential jumps from one node to the other.
Many nerve fibres are bunched together to form a nerve. The bundles of fibres are enclosed within connective tissue called the epineurium.
T.S of Myelinated Nerve and Diagram of a Section of Myelinated Nerve
