2. Saltatory Conduction: An AP can propagate along an axon much faster with this method and occurs in Myelinated Axons . There are few voltage-gated channels present in myelinated regions of axons. In contrast, there are many located in the unmyelinated areas known as the nodes of Ranvier. Therefore, current carried by Na+ and K+ flows across the membrane mainly at the nodes. The AP (electrical current carried by the ions) flows through the ECF surrounding the myelin sheath and through the cytosol from one node to the next. The flow of current across the membrane only at the nodes of Ranvier has 2 consequences: 1. The AP appears to “leap” from node to node. Because of this, an AP travels much faster than it would on an unmyelinated axon. 2. Opening channels only at the nodes, represents a more energy-efficient mode of conduction. Therefore, less ATP is used for the Na+/K+ pumps.
The speed of propagation of an AP is affected by 3 major factors :
1. Amount of myelination : as mentioned above, an AP propagates along a myelinated axon much faster than an unmyelinated axon. 2. Axon diameter : larger diameter axons propagate an AP faster than smaller ones due to a larger surface area. 3. Temperature : Axons propagate an AP at lower speeds when cooled.
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