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Schwann Cells and Unmyelinated Axons

  • In the peripheral nervous system, Schwann cells also surround and give support to small-diameter axons (C fibers; 2 um or less).
  • A series of Schwann cells covers the length of each axon. Abutting Schwann cells are tightly joined and nodes of Ranvier do not form.
  • Each Schwann cell typically contains several axons (up to 20), which are often brought into the cell by image descriptioninvaginations of the plasma membrane.
  • The internalized image descriptionaxons are not myelinated by the Schwann cell.
An image showing schwann cell containing several small-diameter axons after Invagination
An image showing schwann cell containing several small-diameter axons
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  • Instead, they are held in longitudinal image descriptionchannels created by the invaginatedĀ plasma membranes.
An image showing schwann cell containing several small-diameter axons
An image showing schwann cell containing several small-diameter axons and labels for channels and small axons
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  • Indentations of the Schwann cell plasma membrane called image descriptionmesaxons connect the channels to the cell surface.
An image showing schwann cell containing several small-diameter axons and labels for channels and small axons
An image showing schwann cell containing several small-diameter axons and labels for channels, small axons and mesaxons
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  • Narrow openings between the paired mesaxon membranes allow extracellular fluids and ions to image descriptionfreely move in and out of the channels and circulate around the embedded axons.
  • Thus, even though small axons reside inside Schwann cells, they are still fully exposed to the extracellular environment.
  • As a result, action potentials are generated along the entire length of small axons and saltatory (jumping) conduction doesn’t occur.

Overview:

An image showing schwann cell containing several small-diameter axons, channels, mesaxons and small axons are numbered without answers
An image showing schwann cell containing several small-diameter axons, channels, mesaxons and small axons are numbered and labeled showing the answers
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