Myelinated axons transmit action potentials faster than unmyelinated axons.

Select the best option from the following statements.

(a) Saltatory conduction occurs in myelinated axons.

(b) Myelin has whitish appearance.

(c) Schwann cells are associated only with myelinated fibres.

(d) Voltage-gated sodium channels are absent at nodes of Ranvier.

In myelinated axons, voltage-gated sodium ion channels are confined to the nodes of Ranvier and hence depolarisation occurs only at the nodes but not internodes. This type of conduction is called ‘saltatory’ conduction since the action potential appears to “leap” from node to the next node. Saltatory conduction is much faster than continuous conduction that occurs in unmyelinated axon of the same diameter. The whitish appearance of myelin has nothing to do with the conduction speed. Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon.