---
title: "Ion Channels: Selectivity, Gating and the Evidence from Single Channels"
description: "A channel passes one ion species far better than another because of the chemistry lining its narrowest point, and it opens in response to voltage, a ligand or a mechanical pull. Recording one channel "
canonical: https://lightmysky.com/learn/science/ion-channels-selectivity-gating-and-the-evidence-from-single-channels-mt_2xPzPeXZZ_
source: https://lightmysky.com/learn/science/ion-channels-selectivity-gating-and-the-evidence-from-single-channels-mt_2xPzPeXZZ_.md
retrieved: 2026-09-12
---

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# Ion Channels: Selectivity, Gating and the Evidence from Single Channels

A channel passes one ion species far better than another because of the chemistry lining its narrowest point, and it opens in response to voltage, a ligand or a mechanical pull. Recording one channel at a time shows it flicking between full open and shut rather than easing part way.

Subject: Science · Area: Organisms & Life Processes · Ages 19 to 20
Page: https://lightmysky.com/learn/science/ion-channels-selectivity-gating-and-the-evidence-from-single-channels-mt_2xPzPeXZZ_

## Ready when they can

- Explains selectivity from the pore lining rather than from the size of the hole alone.
- Reads a single-channel trace as open and closed states, and links their proportions to a whole-cell current.
- Names the three gating cues and gives a cell that uses each.

## Lesson: Picky gates that snap open

A channel passes one ion species far better than another because of the chemistry lining its narrowest point. Amino acids there space their charges so that matching ions shed their water and slip through, while others are held back. Selectivity is chemistry, not just the size of the hole.

These gates let you think, move, and feel touch, and they open to three cues. Voltage-gated channels, like the sodium channels of a neuron, open when the membrane passes threshold. Ligand-gated channels, like those on a muscle fiber at a synapse, open when a chemical docks. Mechanically gated channels, like those in a touch receptor cell, open when pulled.

**Example.** Recording one channel at a time shows it flicking between full open and shut in square jumps, never easing part way. The whole-cell current is the number of channels times the single-channel current times the fraction of time each spends open, so more open time means more total current.

The action potential runs on the same all-or-nothing logic as one channel. Past threshold it fires its full spike on its own, like a light switch, and the rising phase is voltage-gated sodium channels opening so sodium rushes in. Later those sodium channels inactivate while potassium leaves, and the voltage falls back.

**Recap.** Pore chemistry picks the ion, three cues open the gate, and each channel is all or nothing.

## 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)
- [Membrane Lipid Composition, Asymmetry and Fluidity](https://lightmysky.com/learn/science/membrane-lipid-composition-asymmetry-and-fluidity-mt_PIk59MG-gN)
- [Co-transport and Coupled Movement Across Membranes](https://lightmysky.com/learn/science/co-transport-and-coupled-movement-across-membranes-mt_pzQ8n3FWNV)

## Opens up

- [Ligand Binding: Dissociation Constants and Receptor Occupancy](https://lightmysky.com/learn/science/ligand-binding-dissociation-constants-and-receptor-occupancy-mt_i-v79OaM0n)
- [From Photons to Spikes: the Retina](https://lightmysky.com/learn/science/from-photons-to-spikes-the-retina-mt_kviN7WskmP)
- [Hearing and Balance: Frequency, Place and Head Motion](https://lightmysky.com/learn/science/hearing-and-balance-frequency-place-and-head-motion-mt_qzPAt9JMOZ)