The soma fires a spike that travels the axon as a depolarization wave — coloured segments along the tube show the wave front moving from soma to terminal. Where the 2D version plots voltage as a flat trace against time, this scene renders the wave and its consequence spatially: when the wave reaches the axon terminal, voltage-gated Ca²⁺ influx triggers synaptic vesicles to fuse with the membrane and release neurotransmitter into the synaptic cleft. Each release is an individual particle crossing the cleft in 3D and binding a receptor on the postsynaptic membrane, which is what actually depolarizes the next cell — not the axon's own wave directly.
wave: position(t) = soma + v_cond·t (v_cond ↑ when myelinated)
at terminal: P(release) = release_probability per docked vesicle
postsynaptic ΔV ∝ Σ bound receptors (decays over time)
- Firing rate — how often the soma launches a new wave down the axon.
- Release probability — chance each docked vesicle actually fuses and releases when a wave arrives; real synapses are unreliable, not all-or-nothing.
- Vesicles per spike — how many vesicles are docked and available to release on a given spike.
- Myelinated — swaps continuous propagation for saltatory jumps between visible nodes of Ranvier, several times faster to cross the same axon.
Real-world relevance: this two-stage relay — electrical wave along the axon, then chemical handoff at the synapse — is why synaptic drugs (SSRIs, curare, botulinum toxin) act at the cleft rather than on the axon itself, and why transmission here is probabilistic rather than perfectly reliable.