How a charged membrane becomes a message — the spark, the wave, and the leap across the gap.
A resting neuron sits at about −70 mV — the inside is more negative than the outside.
The Na⁺/K⁺ pump uses ATP to push 3 Na⁺ out for every 2 K⁺ in, building the gradients.
K⁺ leaks back out and large negative proteins stay trapped inside — so the inside stays negative.
Tap a part of the neuron to see what it does.
Tap a part on the left, or a button, to see its role.
Hit Fire to sweep the impulse in real time — or drag along the trace to inspect any moment. Watch the Na⁺ and K⁺ channels open and close. Then switch the stimulus to test all-or-nothing.
The Na⁺/K⁺ pump keeps the inside at about −70 mV. Voltage-gated channels are closed.
At the gap, the signal becomes a molecule. Tap each step.
The synapse converts an electrical impulse into a chemical signal, then back again.
Want the full detail — Ca²⁺ influx, exocytosis, receptor binding, and ACh recycling? See the Synaptic Transmission deep dive.
Myelin insulates the axon, so depolarisation only happens at the nodes of Ranvier. The impulse jumps node to node — much faster.
Conduction is faster with more myelin, a wider axon, and a higher temperature — up to ~120 m/s.
Excitatory neurotransmitters depolarise (EPSP, toward threshold); inhibitory ones hyperpolarise (IPSP, away from threshold).
A neuron sums all its inputs — only if the total reaches threshold does it fire (all-or-nothing).
Every piece you've met is one link in a chain. Tap a concept to light up how it connects.
A signal begins as a stimulus, becomes an electrical spike in a neuron, crosses the synapse as a chemical neurotransmitter, and ends as a response. Tap a concept to trace how it connects.
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 — they fit nowhere.
Single best answer, Paper 1 style. Pick one — you'll see why.