NP Myelin

What is myelin?

Myelin is a multi-layered, compacted membranous sheath that surrounds axons in the peripheral (PNS) and central nervous systems (CNS) to increase the conduction speed in the nervous system.

What is myelin composed of and how is it organised?

It is a multi-layered structure primarily composed of lipids and expresses unique proteins that facilitate its dense compaction.

Myelin is clustered into internodes which are found between the nodes of Ranvier gaps.

What are the cell types that give rise to myelin?

Schwann Cells:

• PNS

• provide myelination, with one cell typically myelinating a single axon (1:1 myelination).

Oligodendrocytes:

• CNS

• can myelinate multiple axons (50:1 myelination).

Identify six advantages that myelin confers to the neuron

• Increased Conduction Velocity: Myelin enables saltatory conduction by changing the capacitance of the axon, allowing action potentials to jump from node to node, greatly increasing the speed of signal transmission.

• Metabolic Efficiency: Myelination reduces the amount of energy required for nerve impulse conduction by minimizing the continuous depolarization along the axon, allowing for greater metabolic efficiency.

• Allows for more compact nervous system

• Compartmentalization of Axons: Periaxonal space is really important for transferring substrates from axon to oligodendrocyte

  • Transporters exist upon myelin and axon membranes, allowing for glucose and lactate to shuttle between the oligodendrocyte and the axon, giving the mitochondria in the axon energy in which to operate

• Myelin adapts with experience and is required for learning

• Myelin can repair itself