How Neurons Send Signals: Action Potentials and Synapses

BiologyCell BiologyCommunity

A chain of three neurons passes electrical signals along axons and chemical signals across synapses. A live graph shows the membrane potential of the chosen neuron, with the resting potential, the threshold and the phases of the action potential. Students change stimulus strength, threshold, pulse frequency, neurotransmitter release and myelination and see how each one changes the signal.

Lesson: Neurons rest at about -70 mV. A stimulus that raises the membrane potential to the threshold (about -55 mV) triggers an action potential. Na+ channels open and the inside becomes positive (depolarisation, up to about +40 mV). K+ channels then open and the potential falls again (repolarisation), dipping below the resting level. During the refractory period that follows, a new stimulus cannot start another spike, so the signal only travels forward along the axon. Action potentials are all-or-nothing: a stronger stimulus does not make a spike taller, it makes spikes happen more often. Myelin insulates the axon, so the signal travels faster. At the synapse, neurotransmitter crosses the gap and binds to receptors on the next neuron. If too little is released, the next neuron stays below threshold and does not fire.

Created by a teacher with Simulic AI and reviewed by the Simulic team.