---
title: "Synaptic Transmission, Summation and Inhibition"
description: "Calcium entry makes vesicles release transmitter, which binds receptors on the next cell. Several small inputs can add up, and some synapses make the next cell harder to fire rather than easier."
canonical: https://lightmysky.com/learn/science/synaptic-transmission-summation-and-inhibition-mt_0uM8xRV92B
source: https://lightmysky.com/learn/science/synaptic-transmission-summation-and-inhibition-mt_0uM8xRV92B.md
retrieved: 2026-09-12
---

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# Synaptic Transmission, Summation and Inhibition

Calcium entry makes vesicles release transmitter, which binds receptors on the next cell. Several small inputs can add up, and some synapses make the next cell harder to fire rather than easier.

Subject: Science · Area: The Human Body · Ages 17 to 18
Page: https://lightmysky.com/learn/science/synaptic-transmission-summation-and-inhibition-mt_0uM8xRV92B

## Ready when they can

- Orders the steps from an arriving impulse to a response in the postsynaptic membrane.
- Distinguishes spatial from temporal summation with an example of each.
- Explains how an inhibitory synapse acts on the postsynaptic membrane.

## Lesson: Votes at the Hillock

A spike cannot jump the cleft, so it turns chemical. The arrival opens voltage gated calcium channels, calcium pulls vesicles onto the membrane, and transmitter bursts out. It diffuses across in under a millisecond, docks on receptors, and the membrane answers.

One input rarely decides anything. Repeats from one synapse pile up in time, which is temporal summation, like repeat taps pushing a door. Simultaneous inputs from several synapses pile up across space, which is spatial summation, like friends pushing together.

**Example.** The axon hillock adds the votes. Excitatory inputs depolarise toward threshold while inhibitory ones hyperpolarise away. Enough net excitation fires the next spike, or the cell stays silent.

**Tip.** Inhibition is active braking, not missing excitation. Transmitters such as GABA open chloride or potassium channels, so the membrane sits further from threshold. Enzymes then clear the cleft, for example acetylcholinesterase splitting acetylcholine, so each signal stays brief.

**Recap.** Calcium releases transmitter, weak inputs add up in time or across space, and inhibition votes the cell further from firing.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Conduction Speed: Myelination and the Refractory Period](https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6)

## Opens up

- [The Sliding Filament Model of Muscle Contraction](https://lightmysky.com/learn/science/the-sliding-filament-model-of-muscle-contraction-mt_BsB4s4HfD8)
- [From Photons to Spikes: the Retina](https://lightmysky.com/learn/science/from-photons-to-spikes-the-retina-mt_kviN7WskmP)
- [Touch, Temperature and Pain](https://lightmysky.com/learn/science/touch-temperature-and-pain-mt_rnSuJA4-kj)
- [Transmitter Systems and Two Kinds of Receptor](https://lightmysky.com/learn/science/transmitter-systems-and-two-kinds-of-receptor-mt_yXaSbrBxua)