Myelination (A-level Biology)
Myelination
Importance of Myelination
Non-Myelinated Axons
- Action potentials are transmitted through non-myelinated axons by a wave of depolarisation.
- When an action potential occurs, some sodium ions will diffuse sideways across the cytoplasm of the neurone. Sodium ions cause the adjacent section of the membrane to depolarise, opening voltage-gated sodium channels that continue the wave.
Myelinated Axons
- Myelinated axons are those covered with a layer of Schwann cells that act as an insulator.
- This means that action potentials can only occur at the nodes of Ranvier (gaps in the myelin sheath), as this is the only place that sodium ions can cross through the membrane.
- Because of this, action potentials ‘jump’ from one node of Ranvier to the next in a process called saltatory conduction. The cytoplasm conducts enough charge to depolarise the next node.
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