How is myelin sheath formed in PNS?
Myelin is formed by Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Each Schwann cell forms a single myelin sheath around an axon. Myelin itself forms by the spiral wrapping around an axon of an enormously expanded glial plasma membrane that then compacts.
What is the myelin sheath around the PNS called?
In the PNS, myelin protein zero (MPZ or P0) has a similar role to that of PLP in the CNS in that it is involved in holding together the multiple concentric layers of glial cell membrane that constitute the myelin sheath. The primary lipid of myelin is a glycolipid called galactocerebroside.
What is the purpose of the myelin sheath in the PNS?
By imposing saltatory conduction on the nervous impulse, the principal role of the myelin sheath is to allow the faster propagation of action potentials along the axons which it surrounds. Peripheral nervous system (PNS) myelin is formed by the differentiation of the plasma membrane of Schwann cells.
Where does myelination occur first?
Myelination of the corticospinal tract begins at the proximal portion of the axon and the shortest axons are the first to myelinate.
What cells are responsible for the formation of myelin?
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).
What are the three functions of the myelin sheath?
The main functions of the myelin sheath are:
- It acts as an electrical insulator for the neurone – it prevents electrical impulses travelling through the sheath.
- The sheath prevents the movement of ions into or out of the neurone/ it prevents depolarisation.
Can Vitamin B12 deficiency cause demyelination?
Vitamin B12 deficiency is known to be associated with signs of demyelination, usually in the spinal cord. Lack of vitamin B12 in the maternal diet during pregnancy has been shown to cause severe retardation of myelination in the nervous system.
How is the myelin sheath used in the CNS?
The myelin sheath insulates axons of the CNS neurons to ensure that rapid transmission of electric impulses occurs across the nervous system. Within the CNS, the central myelin is generated by oligodendroyctes.
How are myelin sheaths related to Schwann cells?
Myelin sheaths are related to Schwann cells in the same manner that has been described most frequently for the mammalian PNS (Peters et al., 1991). S.S. Scherer, E.J. Arroyo, in Reference Module in Biomedical Sciences, 2014
How is the myelin sheath formed in a glial cell?
During the formation of the myelin sheath, glial cells are squashed into lamellae, the 2 layers of cell membranes are brought into proximity to each other, and the positive charge of MBP and the negative charge of the opposite cell membrane lipids attract each other ( 13) so that the 2 layers of cell membranes are more stably combined.
What happens to the myelin sheath during regeneration?
The major feature during regeneration was the compaction of the myelin sheath, wherein the distance between the 2 layers of cell membrane in the double-bilayer became shorter and the adjacent double-bilayers tightly closed together and formed the major dense line.