True about Schwann cells ?
Ans. is 'c' i.e., Form myelin sheath Shwann cellsIn peripheral nervous system (PNS), Schwann cells provide structural suppo to all nerve fibres. Schawann cells form a sheath around the axon and form the outermost layer of a nerve fiber, called neurilemma, also known as sheath of Schwann or neurolemma. Schwann cells is surrounded by a basal lamina (or external lamina).In some fibres, Schwann cells additionally form myelin sheath; these fibres are called myelinated nerve fibres. Those nerve fibres in which myelin sheath is not formed, that is Schwann cells only provide structural suppo, are non-myelinated nerve fibres.Schwann cells deposit concentric layers of myelin around the axon to form myelin sheath. In myelinated fibres, one Schwann cell covers only a sho segment of the axon. The small pa of the axon present in between two adjacent Schwann cells (the pa that is devoid of myelin sheath) is called node of Ranvier.Myelin is a mixture of lipoproteins and acts as an insulator. Since myelin acts as an insulator, impulses are generated only at the nodes of Ranvier and this helps in faster conduction of the impulses. This is called saltatory conduction.Schwann cells are derived from neuroectoderm.
Pa of central nervous system
Present only in myelinated nerve fibres
Form myelin sheath
Derived from surface ectoderm