Question

The myelin sheath around axon is formed by:

• A. Nodes of ranvier
• B. Synaptic knob
• C. Schwann cells
• D. Both b and c

Answer 1

The correct option is C Schwann cells

Schwann cells are responsible for forming myelin sheath around the axon. They are present in both myelinated nerve fibres and unmyelinated nerve fibres. However they form myelin sheath around the axon in the myelinated nerve fibres.
Nodes of Ranvier are the gaps between two myelin sheath, since it is not a continuous sheath. Synaptic knobs are bulb-like structures present at the distal branched end of the axon. These knobs are composed of synaptic vesicles containing certain chemical substances called neurotransmitters. Hence both nodes of ranvier and synaptic knobs have no role in formation of myelin sheath.