Myelinated axons

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A myelinated axon is one which is surrounded by a myelin sheath, comprised of Schwann cells[1]. It is electrically insulating, except for gaps in the sheath which are called the Nodes of Ranvier. This insulation increases the speed of transmission of action potentials. Due to the gaps in the myelin sheath, action potentials propagate by saltatory conduction. Where action potentials jump between the nodes, there is a higher abundance of ion channels. Conduction in myelinated axons is faster than in an unmyelinated axon as the impulse 'jumps' from one Node of Ranvier to another[2]. Myelinated axons may become demyelinated, there are a number of factors which can cause this, one includes inflammation. Demyelination causes issues with conduction and can cause a series of issues with the brain and body which can potentially lead to chronic diseases, an example of this would be Multiple Sclerosis[3]. Demyelination causes inefficeint saltatory conduction as depolarisation must also occur at the gaps in the myelinated sheath, decreasing the speed of impulse transmission.

References

  1. Lodish, Laisser, Bretscher, Amon, Berk, Krieger, Ploegh, Scott (2012) , Molecular Cell Biology, 7th Edition, New York, WH Freeman
  2. Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walters P. (2008). Molecular biology of the cell. 5th ed. New York: Garland Science. p680.
  3. Healthline. Demyelination: What Is It and Why Does It Happen? 2017. [cited 20/11/17]; Available from: https://www.healthline.com/health/multiple-sclerosis/demyelination#overview1
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