Question

The nodes of Ranvier are:
A. The points in which the axons are exposed.
B. The contact points found over the non-myelinated nerve fibre.
C. Areas in which the axons swell up.
D. Areas where the neurilemma touches the axon.

Answer 1

Hint:
The nodes of Ranvier are the specialized regions in the axonal membrane that are not insulated by the myelin.

Complete answer:
The node of Ranvier serves as a gap in the insulating (myelinated) neuron which helps in the rapid conduction of nerve impulses. This is only seen in some types of neurons whose axons are myelinated. In saltatory conduction, the nodes of Ranvier will interrupt the insulation at different intervals, and due to this discontinuity, the impulses jump from one node to another node.
Hence, the nodes of Ranvier are observed where the axons are non-myelinated. Myelin is observed around the axons, which slows the signal passing through the neurons. Hence, nodes of Ranvier are observed in the points in which axons are exposed.
Nodes of Ranvier help to expose the neuron membrane to the external environment. These gaps are rich in ion channels, which help to exchange certain ions. Mainly sodium and chloride ions are observed in these channels, which are required to make an action potential. The stimulus propagated by one node of Ranvier jumps to a subsequent node along the axon, thereby enabling the nerve impulse to speed along the fiber. The movement of sodium ions which is required to depolarize the membrane will occur at the Node of Ranvier only because the sodium voltage-gated channels are found only at the nodes of Ranvier

Option ‘A’ is correct

Note:
An action potential is the reversal of electrical polarization of the neuron membrane that initiates or is a component of a wave of excitation that travels along the axon.