Cable Properties and Dendritic Integration
A voltage change spreads along a dendrite and fades with distance, at a rate set by membrane resistance and internal resistance. Inputs arriving close together in time and space add up, and only their sum at the trigger zone decides whether a spike is fired.
What a learner can do afterwards
- Explains why a distant synapse contributes less than a nearby one of the same size.
- Predicts the effect of a thicker axon or more myelin on how far a signal spreads.
- Combines several inputs at the trigger zone rather than judging each on its own.
1 · Read
A pulse entering a dendrite fades as it travels. Leaky walls drain it and thin cores resist it, so a far synapse pushes less at the trigger zone than a near one of equal size. Distance taxes every signal.
Width and wrapping set the tax rate. A thicker core resists less, so the pulse reaches further. Myelin wraps the line, plugs the leaks, and lets the pulse glide on to the trigger zone.
Picture two equal taps, one near the trigger zone and one far out. The near tap lands hard while the far tap arrives faint. Fire both near taps at once and their sum may cross threshold, though each alone would fail.
Never judge one input alone. Add close ones in space and time at the trigger zone, then ask if the sum crosses threshold.
Distance fades each pulse, width and myelin spare it, and only the summed push decides the spike.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.