The correct option is A synaptic vesicle
Synapses, also called neuronal junctions, are the junctions between two or more neurons where impulses pass from one neuron to others.
A presynaptic neuron is a neuron from which information passes through the synapse and the neuron which receives the information is the postsynaptic neuron.
The space between the presynaptic and postsynaptic membrane is called the synaptic cleft.
The terminal of presynaptic neurons usually ends in a small bulbous enlargement called the synaptic knob. This knob contains numerous synaptic vesicles and dense tufts.
Synaptic vesicles contain neurotransmitters like acetylcholine, gamma-aminobutyric acid, glycine, neuropeptides, catecholamines, etc.
Myelin sheath is formed by Schwann cells which are found outside the neuron.