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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.

Learn the anatomy of the nervous system fast and effectively using this guide full of interactive quizzes and worksheet activities.

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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