Consider two types of nerve fibres in the human neural system: Fibre A is extracted from a cranial nerve, and Fibre B is extracted from a nerve of the autonomous neural system. Which of the following correctly describes the primary structural difference between Fibre A and Fibre B regarding their coverings?

Step-by-step solution

According to NCERT, cranial nerves contain myelinated nerve fibres, whereas the autonomous neural system contains unmyelinated nerve fibres. Myelinated nerve fibres (Fibre A) are enveloped with Schwann cells which form a myelin sheath around the axon. Unmyelinated nerve fibres (Fibre B) are also enclosed by a Schwann cell, but this cell does not form a myelin sheath around the axon. Therefore, Fibre A has a myelin sheath formed by Schwann cells, while Fibre B is enclosed by Schwann cells but lacks a myelin sheath.