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.
What a learner can do afterwards
- 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.
1 · Read
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.
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.
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.
Calcium releases transmitter, weak inputs add up in time or across space, and inhibition votes the cell further from firing.
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.