Question

Read the following statements:
(i) Saltatory type of present in non-myelinated nerve fibres (axons) only
(ii) The nerve impulse generated at a point in the neuron faes resistances at sites where myelin sheath is present
(iii) Nodes of Ranvier of axon is exposed to ECF
(iv) In myelinated neurons, ion channels and transport pumps are absent in the nodes of Ranvier
(v) In myelinated nerve fibre, the nerve impulse travel as a continous wave of depolarisation
How many of the statements are correct?

• A. Three
• B. Two
• C. Five
• D. Four

Answer 1

The correct option is A Three

Correct statements are ii, iii and v.

ii) Because myelin sheet acts to speed up impulses and acts as an insulator, which does not allow the current to flow through the segments that lie between the nodes of Ranvier.

iii) The nodes of Ranvier, being exposed to the ECF every 1 mm which contain large amounts of voltage-gated sodium channels. This increases sodium’s ability to travel along the axon to regenerate the action potential.

v) Because only the nodes of Ranvier are excited during conduction in myelinated fibers, ${Na}^{+}$ flux into the nerve is much less than in unmyelinated fibers, where the entire membrane is involved.

So, the correct answer is three.