An electrical signal reaches a gap it cannot cross. So the neuron does something clever — it turns the message into a chemical, throws it across, and turns it back into electricity on the other side.
Companion to the Action Potentials lesson — this one goes deep on just the crossing.
A synapse is the tiny gap between a neuron and the next cell. An electrical impulse can't jump it — the signal has to change form to get across.
The presynaptic neuron converts its electrical impulse into a chemical neurotransmitter, which crosses the cleft and is turned back into an electrical signal on the other side.
Vesicles and neurotransmitter sit on the presynaptic side; receptors sit on the postsynaptic side. So signals travel one way — the synapse enforces direction.
Tap a part to see its job in the crossing.
Tap a part to see its job in the crossing.
Press play to watch all eight steps unfold, or step through them yourself.
Press play to watch, or tap a number to jump to a step.
Once it has fired the message, acetylcholine must be cleared fast — or the postsynaptic cell never stops firing. Tap a step in the loop.
ACh is built, fires the signal, then is broken apart and rebuilt. Tap a step.
Tap a concept to light up how it connects.
The synapse turns an electrical signal into a chemical one and back again. Tap a stage to trace the chain — and notice how it loops: the Na⁺ that enters can reach threshold and fire a brand-new action potential.
Tap any concept to trace its connections · tap the background to reset
Drag each term into the gap it belongs in. Two terms are traps.
Single best answer, Paper 1 style. Pick one — you'll see why.