axon cable properties

Axon cable properties are the plain electrical habits of a neuron's long output wire — the axon — treated like a real-life cable. Just as an old undersea telegraph wire leaks and blurs the signal you push into one end, a stretch of axon is not a perfect conductor: as a voltage change spreads along it, the signal gets weaker and slower the farther it travels. Two physical features set this behavior. One is resistance, which is how hard it is for electric charge to flow — there is resistance to current running lengthwise down the inside of the axon, and a separate resistance to current leaking sideways out through the wall (the membrane). The other is capacitance, the membrane's ability to store charge like a tiny battery that must be filled up before the voltage on the other side can change.

These two features together decide two things engineers and neuroscientists care about: how far a signal reaches and how fast it gets there. A fatter axon with a tightly sealed, low-leak wall lets charge run far before it drains away, so a voltage bump can travel a long distance before fading out — this reach is captured by a number called the length constant (the distance over which the signal shrinks to about a third of its starting size). Speed, meanwhile, is slowed mainly by capacitance: every patch of membrane must be charged and discharged like filling and emptying a bucket, and more capacitance means more time. This is exactly why thickening the axon and wrapping it in fatty myelin insulation — which lowers leak and capacitance — makes nerve signals travel both farther and faster, and why these passive cable properties shape how quickly you feel a touch or move a muscle.