--- title: "Cable Properties and Dendritic Integration" description: "Passive graded voltage changes weaken with distance in a uniform dendritic cable model. Axial resistance, membrane resistance and capacitance affect signal spread. Synaptic effects combine in space an" canonical: https://lightmysky.com/learn/science/cable-properties-and-dendritic-integration-mt_bbPl-eJUFF source: https://lightmysky.com/learn/science/cable-properties-and-dendritic-integration-mt_bbPl-eJUFF.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Cable Properties and Dendritic Integration Passive graded voltage changes weaken with distance in a uniform dendritic cable model. Axial resistance, membrane resistance and capacitance affect signal spread. Synaptic effects combine in space and time, including inhibition. Predicting a spike also requires considering threshold and channel availability; real dendritic integration can be nonlinear. Subject: Science · Area: The Human Body · Ages 18 to 20 Page: https://lightmysky.com/learn/science/cable-properties-and-dendritic-integration-mt_bbPl-eJUFF ## Ready when they can - Predict the trigger-zone effects of equal local voltage changes at different distances in a uniform passive dendritic cable. - Distinguish axial resistance from membrane resistance and predict effects of cable diameter or axonal myelin on passive spread. - Distinguish spatial and temporal summation, combine signed input effects in a stated linear model, and account for channel availability when predicting a spike. ## Lesson: Fading signals that add up to a spike Synaptic inputs change voltage locally in dendrites. The trigger zone, usually the axon initial segment, is where spikes commonly begin. In a uniform passive-cable model, a graded voltage change gets smaller as it spreads. Current leaks across the membrane and meets axial resistance inside the cell. Equal local voltage changes farther away have a smaller effect at the trigger zone in this model. A regenerated action potential does not fade this way. *(drawing: This sequence describes passive attenuation. It does not show a regenerated action potential shrinking.)* A wider cable has lower axial resistance per unit length. With other membrane properties comparable, a fixed local voltage change can spread farther. Higher membrane resistance also reduces leakage. Myelin surrounds axons, raises membrane resistance and lowers capacitance, so less charge is needed for a voltage change. Passive current spreads between nodes, where spikes regenerate. Ordinary dendrites are not myelinated. Spatial summation combines effects from different synapses. Temporal summation combines repeated inputs from one synapse before earlier effects fade. Overlapping excitatory effects may reach threshold together even when each alone is too small. Inhibitory inputs can oppose depolarisation or reduce excitation by increasing membrane conductance. **Example.** For a linear approximation, add signed voltage effects already measured at the trigger zone and overlapping at the same moment. Suppose reaching threshold requires a change of +15 mV from rest. Effects of +9 mV, +8 mV and -4 mV give 9 + 8 - 4 = +13 mV. The total is below +15 mV, so these inputs do not reach threshold. Ignoring inhibition would give +17 mV and a different prediction. Real synaptic effects need not add linearly. *(drawing: These are effects at the trigger zone in the stated linear model, not voltage changes at the original synapses.)* Reaching threshold can start a spike if the trigger-zone membrane is able to respond. During the absolute refractory period, sodium-channel inactivation prevents another spike there. Real dendrites can contain active channels that amplify or generate local signals. This can change the effect of distant inputs, so the passive-cable comparison is not a rule for every neuron. **Recap.** Cable properties affect passive voltage spread. Excitatory and inhibitory effects combine in space and time. A spike needs threshold and responsive channels; real integration can be nonlinear. *Lesson, questions and flashcards written for this dataset about passive voltage spread, cable properties and synaptic integration.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Channel Kinetics and the Ionic Basis of the Spike](https://lightmysky.com/learn/science/channel-kinetics-and-the-ionic-basis-of-the-spike-mt_47-LDzgcKp) ## Optional connections - [Conduction Speed: Myelination and the Refractory Period](https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6) ## Opens up - [Building a Visual Scene: Pathways, Maps and Receptive Fields](https://lightmysky.com/learn/science/building-a-visual-scene-pathways-maps-and-receptive-fields-mt_wOc4YpkdYL)