Myelination & Saltatory Conduction (Edexcel International A Level Biology)

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Naomi H


Naomi H



Myelination & Saltatory Conduction

  • In unmyelinated neurones the speed of conduction is relatively slow because depolarisation must occur along the whole membrane of the axon
  • By insulating the axon membrane myelin increases the speed at which action potentials can travel along the neurone
    • In sections of the axon that are surrounded by a myelin sheath depolarisation cannot occur as the myelin sheath stops the diffusion of sodium and potassium ions
    • Action potentials can only occur at the nodes of Ranvier 
      • Nodes of Ranvier are the gaps between the Schwann cells that make up the myelin sheath
    • Sodium ions diffuse along the axon within the Schwann cells and the membrane at the nodes of Ranvier depolarises when the sodium ions arrive
      • The diffusion of sodium ions in this way is known as local currents, or local circuits
    • The action potential therefore appears to ‘jump’ from one node to the next; this is known as saltatory conduction
  • Saltatory conduction allows the impulse to travel much faster than in an unmyelinated axon of the same diameter

Saltatory conduction (1)Saltatory conduction (2)

Action potentials are transmitted along myelinated axons by saltatory conduction

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Naomi H

Author: Naomi H

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.