Synaptic vesicles, also known as neurotransmitter vesicles, are the portion of the axon terminal where neurotransmitters are stored before being released across nerve synapses. These vesicles are essential for propagating nervous impulses across synapses and are constantly being recreated. The portion of the axon that holds the group of vesicles is called the axon terminal or the bouton. This mechanism was not discovered until the 1950's when the invention of the electron microscope made the synaptic vesicles visible. The synaptic vesicles are vulnerable to the ingestion of neurotoxins such as botulinum, tetanus, and some spider venoms.