A synaptic vesicle belonging to the pool of vesicles that are the first to be released as a result of chemical or electrical stimulation e.g. by an action potential, have the highest presynaptic membrane fusion probability and correspond to about 1% of the total number of synaptic vesicles at a resting terminal bouton. [ http://www.ncbi.nlm.nih.gov/pubmed/22745285 GOC:pad ]