Figure 1.

Schematic representation of volume and wiring transmission. (A) Simplified axonal varicosities displaying volume transmission in which the neurotransmitter is released in the extracellular space, where it diffuses and reaches metabotropic receptors located on nearby cells. (B) Simplified axonal varicosities showing wiring transmission. Each varicosity establishes a synaptic contact with specific postsynaptic element, and the neurotransmitter is released in a confined space, where it interacts with both ionotropic and metabotropic receptors.