Myelin sheath, Schwann cells, oligodendrocytes, insulation of axon

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Oligodendrocytes and Schwann cells are types of neuroglia cells that produce myelin sheath, which acts as insulation along the axon.

Most mammalian nerves are surrounded by a whitish, fatty layer called the myelin sheath (not part of the neuron.) The myelin sheath insulates the nerve fibres to prevent signal loss or crossing of signals. Just like insulation prevents wires next to each other from accidentally discharging each other. Also, myelin increases the speed of conduction in the axon. Schwann cells are neuroglia cells that support neuronal function by increasing the speed of impulse propagation. Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system are types of neuroglia cell that produce myelin. At certain intervals along the axon, there are small breaks in the myelin sheath with exposed areas of axon membrane called nodes of Ranvier.

This image illustrates the parts of a neuron, depicted as a nucleus surrounded by a randomly shaped cell body with many arm-like dentrites on its edges. The dendrites receive incoming signals. The axons send signals away from the neuron cell body, represented as beads on a chain in the picture. The myelin sheath surrounds and insulates the axon beads, the node of Ranvier links each axon to the next one, and the Schwann cells inside each axon increase the speed of the signal as it moves towards the axon terminal. The axon terminal is shown as several branches emerging from the last axon in the chain.

Neuron: The myelin sheath surrounds and insulates the axon.

Practice Questions

 Khan Academy   

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Demyelinating disease and aging

MCAT Official Prep (AAMC)


Key Points

• A whitish, fatty layer called the myelin sheath (not part of the neuron) acts as insulation of axon, prevents loss or crossing of neural signals, and increases the speed of conduction in the axon.

• Schwann cells are neuroglia cells that support neuronal function by increasing the speed of impulse propagation; it produces myelin sheath

• Oligodendrocytes line up along the nerves and also produce an insulating cover called myelin sheath; they are found in the CNS.


Key Terms

myelin: a substance produced by cells of the neuroglia that increases the speed of impulses along the axon of the neuronal fibre

neuroglia: supporting cells in nervous tissue

myelin sheath: acts to protect the nerves from other electrical impulses, and speeding the time it takes for a nerve to traverse an axon

Schwann cells: glial cells that support nerve regeneration

oligodendrocytes: neuroglia cell that produces myelin

node of Ranvier: a small constriction in the myelin sheath of axons

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