Explore the system
Inside a working synapse
Follow an electrical signal into a chemical message, then trace its clearance and recycling.
Sources and model limits
Original schematic. Positions show relationships; structures and concentrations are not to scale.
- Julien's Primer of Drug Action · 15 · 2 · Inside a working synapse · PDF 26, 27, 30, 31 · 2.11, 2.17, 2.18
Course notes and existing practice
What you will understand
Explain and operate calcium-dependent release, reversible receptor interaction, termination and separate vesicular loading.
1. Release the signal
An action potential arrives at the terminal. Voltage-gated calcium channels open under that electrical condition, and calcium enters. A vesicle may dock before calcium entry, but fusion in this model requires calcium. Its membrane fuses with the presynaptic membrane; distinct transmitter molecules enter the cleft. An intact vesicle does not cross the cleft.
2. Bind to a receptor
A compatible transmitter binds and unbinds at a receptor. In the ionotropic example, binding changes channel gating. Separate ions move through the pore. Transmitter is neither an ion nor cargo that travels through that pore.
Ending the signal
Routes vary by transmitter system. Diffusion is passive; metabolism changes molecular identity; reuptake changes location. Routes may operate concurrently on different molecules. This activity models diffusion and recycling. It does not place a generic enzyme in every cleft or require each molecule to follow every termination route.
Reloading a vesicle
A membrane transporter brings transmitter into terminal cytosol. A different transporter loads a reserve vesicle. The first transporter stays in the plasma membrane. A recycled molecule can also be metabolized within the terminal; reuptake is not automatic repackaging.
Model boundaries
Token quantities, capacities and logical steps are game parameters, not physiological constants. The approximate one-vesicle-per-action-potential statement is not scored as a universal rule.
Calcium supports release; transmitter binds outside an ion pore. Membrane uptake and vesicular loading are separate. Boxes group related structures; positions are illustrative, not anatomical scale. Read the accompanying lesson for causal and alternative routes.
Adapted from the architecture digest and selected professor-deck pages inspected for this slice. Transcript wording remains digest-attributed. Diagrams are original and do not reproduce source images.
Adapted from the architecture digest and selected professor-deck pages inspected for this slice. Transcript wording remains digest-attributed. Diagrams are original and do not reproduce source images.