Myelin sheath

Author: Scott A. Sheffield MS

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Myelin sheaths are made of a fatty substance and insulate a nerve to increase its signal speed. In the peripheral nervous system (PNS) they are produced by Schwann cells, in the central nervous system (CNS) by oligodendrocytes.

  • Each Schwann cell myelinates only a small portion (0.3 mm to 1.5 mm) of an axon.
  • The minute gaps that occur between adjacent myelin sheaths are called image descriptionnodes of Ranvier.
An image showing an axon of a neuron Myelinated by Schwann Cells without labels
An image showing an axon of a neuron Myelinated by Schwann Cells forming Nodes of ranvier, (Node of ranvier, Dendrites and cell body, Myelin sheath, Myelin sheath, Axon) are numbered without answers
An image showing an axon of a neuron Myelinated by Schwann Cells forming Nodes of ranvier, labels for (Node of ranvier, Dendrites and cell body, Myelin sheath, Myelin sheath, Axon)
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  • In these areas, the axon is exposed to the surrounding environment and proteins embedded in the plasma membrane can produce action potentials (electrochemical impulses).
  • Thus, when action potentials travel down a myelinated axon, they appear to jump from node to node.
  • This process is termed image descriptionsaltatory conduction, and it is used to transfer information quickly, such as to and from the skeletal muscles.

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Histology aspect:

An image showing light micrograph of myelinated neurons at high magnification
Micrograph of myelinated axons
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Overview:

An image showing an axon of a neuron Myelinated by Schwann Cells forming Nodes of ranvier, (Node of ranvier, Dendrites and cell body, Myelin sheath, Myelin sheath, Axon) are numbered and answered below
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