Figure 5.

Model for synapse growth by quantal addition of AMPA-containing trans-synaptic modules. (a) Silent synapses are small, with a PSD area of approximately 0.03 µm² (figure 3b), and are characterized by a matrix with approximately three docked vesicles and no AMPA receptors. A silent synapse (matrix only) can become activated by the addition of an AMPA/PSD-95 nanocluster, which increases the PSD area to approximately 0.04 µm² (figure 3b) and increases the mean vesicle number to about eight. (b) Additional rounds of synaptic strengthening can occur by adding more functional modules, each contributing about eight vesicles and approximately 0.04 µm² of PSD area. Note that each nanocluster only takes about 25% of the area of each module, but it is shown as about 50% of the module area solely for the purpose of illustration clarity.