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First exams 2025

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Nerve Conduction Velocity (HL) (HL IB Biology)

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Saltatory Conduction

  • By insulating the axon membrane, the presence of myelin increases the speed at which action potentials can travel along the neurone:
    • The myelin sheath is formed from Schwann cells
    • In sections of the axon that are surrounded by a myelin sheath, depolarisation (and the action potentials that this would lead to) cannot occur, as the myelin sheath stops the diffusion of sodium ions and potassium ions
    • There are small, uninsulated sections of the axon, called the nodes of Ranvier, which contain clusters of ion pumps and channels which allow the action potential to occur
    • As a result, the action potentials ‘jump’ from one node to the next, this is known as saltatory conduction
    • The local circuits of current that trigger depolarisation in the next section of the axon membrane exist between the nodes of Ranvier
    • Saltatory conduction allows the impulse to travel much faster (up to 50 times faster) than in an unmyelinated axon of the same diameter

Saltatory Conduction Diagram

Saltatory conduction (1), downloadable AS & A Level Biology revision notes

Saltatory conduction (2), downloadable AS & A Level Biology revision notes

Transmission of an action potential in a myelinated axon by saltatory conduction

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.