Unmyelinated and Myelinated Axons
Sodium (Na+) / Potassium (K+) Pump (ATPase)
- Sodium-potassium pump (or Na+/K+ -ATPase) are transmembrane proteins that actively transports Na+ ions to the extracellar fluid (ECF) and K+ ions to the intracellular fluid (ICF). The process basically consists of the following steps.
- 3 Na+ ions from the ICF bind to the pump (with ATP or adenosine triphosphate attached).
- The pump is phosphorylated after the third phosphate on the ATP is hydrolyzed by ATPase.
- The Na+ are released to the ECF as the pump changes conformation (shape).
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- Two K+ ions from the ECF bind to the pump.
- The attached K+ ions trigger dephosphorylation of the pump.
- The K+ are released to the ICF as the pump changes conformation due to dephosphorylation.
- As a result, both chemical (diffusion) and electrical gradients are created.