ANATOMY

Detailed explanation-1: -The myelin sheath is a greatly extended and modified plasma membrane wrapped around the nerve axon in a spiral fashion [1]. The myelin membranes originate from and are a part of the Schwann cells in the peripheral nervous system (PNS) and the oligodendroglial cells in the central nervous system (CNS) (see Chap. 1).

Detailed explanation-2: -Schwann cells make myelin in the peripheral nervous system (PNS: nerves) and oligodendrocytes in the central nervous system (CNS: brain and spinal cord). In the PNS, one Schwann cell forms a single myelin sheath (Figure 1A).

Detailed explanation-3: -Myelin is an insulating layer, or sheath that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances.

Detailed explanation-4: -Schwann cells (SCs) are the main glial cells of the peripheral nervous system which wrap around axons of motor and sensory neurons to form the myelin sheath.

Detailed explanation-5: -The myelin sheath (MS) surrounding the axon (Ax) and the Schwann cell nucleus (S) are clearly visible. B, Cross section of a bundle of unmyelinated axons of an adult mouse sciatic nerve.