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MCAT Content / Specialized Cell Nerve Cell / Myelin Sheath Schwann Cells Insulation Of Axon

Myelin sheath, Schwann cells, insulation of axon

Topic: Specialized Cell Nerve Cell

Schwann cells, specialized neuroglia cells, produce myelin sheath, which acts as insulation along the axon.

Most mammalian neurones are coated in a whitish, fatty layer called the myelin sheath (not part of the neuron.) It insulates the nerve fibers to prevent signal loss or crossing of signals. Just like insulation prevents wires next to each other from accidentally discharging each other. In addition, myelin increases the speed of conduction in the axon. Schwann cells are neuroglia cells that form the myelin sheath.  

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

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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 specialized neuroglia cells that support neuronal function by increasing the speed of impulse propagation; they produce the myelin sheath


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

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