Synapse sim
Drag an impulse along an axon to a synapse model, step the vesicles releasing transmitter, watch it diffuse across the gap and bind to receptor sites, count the sites bound, block sites with a drug to find when the impulse stops, and try sending an impulse the wrong way.
The synapse: synaptic knob, vesicles of transmitter, synaptic gap, receptor sites; the transmitter diffuses across the gap and binds, starting an impulse in the next neurone; impulses cross in one direction only; a drug that blocks receptor sites · covers the IGCSE, GCSE topic
What the sim shows
The synapse: a teaching model of the junction between two neurones, on a lab bench. Drag the glowing ring (the impulse) along the axon to the synaptic knob. Vesicles release a chemical transmitter, which diffuses across the synaptic gap and binds to receptor sites on the next neurone; when at least 4 of the 8 sites have transmitter bound, an impulse starts in the next neurone. Put the blocker drug into receptor sites and the transmitter cannot bind there: with 5 or more sites blocked, no impulse starts. Sent the wrong way, an impulse stops at the gap, because only the first neurone has vesicles and only the next has receptors: impulses cross a synapse in one direction only. The real gap is about 20 nm wide (model magnification about 700 000 ×) and the crossing takes about 0.5 ms. Simplified on purpose: a teaching model, not to scale: the gap is magnified about 700 000 times; the vesicles are drawn a little small for that scale and the transmitter molecules far larger; each vesicle holds 2 transmitter beads and the next neurone has 8 receptor sites, although a real vesicle holds thousands of molecules and a real membrane has thousands of receptors; the 4 sites needed to start an impulse is an illustrative threshold; one impulse always releases the same 3 vesicles; fused vesicles are shown resting at the membrane; really they merge into it; the transmitter takes a fixed path across the gap, although real molecules spread out at random; the blocker drug is a made-up example of a drug that fits the receptor sites without starting an impulse; the removal of transmitter after each impulse is shown as an extra step, not needed for the exam; the impulse is shown as a glowing ring on the fibre, and each step waits for a click; at real speed the whole crossing takes about 0.5 ms; the colours of the two neurones are a key only; real neurones are not coloured.
- Glowing ring: the impulse
- Section model of a synapse (not to scale)
- Beads: vesicles, transmitter (green) and a blocker drug (purple)
Use it in your lessons
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