Answer:
In general, A/Ps win, but some synaptic signal transduction is much faster.
Step-by-step explanation:
The answer depends on the synapse type:
A high-speed action potential (A/P) moves along an axon at ≈ 1 mm every 8.3 μs (≈ 120 m/s). Arriving at a terminal, the A/P voltage spike causes voltage-gated calcium channels to open, flooding the axon bouton with Ca ++
ions, triggering neurotransmitter release.
Three different types of synapse:
In chemical synapses, transport vesicles dump their payloads into the synaptic gap (via exocytosis), neurotransmitter molecules diffuse across a ≈ 20–40 nm gap, to be sensed by receptor proteins on the post-synaptic cell membrane. Together, this may result in significant synaptic delays (milliseconds).
In electrical synapses, gap junctions open, allowing charged ions (an electric current) to flow cross, with a very short delay from axon bouton polarization ⟶ ion flow ⟶ post-synaptic cell reception.
In retina horizontal cells — said to be using the fastest known synapse type — there is no synaptic delay.