significantly with distance (current escapes through leak channels in the axonal membrane). o Axon’s length constant: the distance over which the voltage change generated by current decays to ~37% to its maximum value. ✔ Value depends on # of leak channels and the axon’s internal resistance to current flow. o The number of leak channels increases with axon diameter while internal resistance decreases as axon diameter goes up. o The thicker the axon = larger length constant o Axon diameter and its length constant affects the speed of action potential propagation b/c the current generated by an action potential at one location must spread passively down the axon before it can depolarize another patch of axonal membrane sufficiently to trigger an action potential there. o However, increasing axon diameter is not an ideal strategy to speed up the propagation of axons because 1. It would take up much more space in the nervous system, which is not smart. 2. It is a costly strategy; it would require a lot of metabolic energy. ● The Effects of Myelination - A trick neurons use to increase action potential propagation is by wrapping their axons in a fatty substance known as myelin (produced by special glial cells). ▪ Myelin Sheath: changes both the axon’s length constant and capacitance (the ability of a system to store an electrical charge) … essentially increasing the speed of travel in which action potentials move along the axon. ± Myelination Increases an Axon’s Length Constant ❖ Myelin sheath - is located around an axon and acts like a layer of insulation that prevents the flow of ions through the leak
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- Summer '19
- axon hillock