How do neurotransmitters work?

Neurotransmitters are the chemical messengers of the body. They are stored within thin-walled sacs called synaptic vesicles, which are located in the axon terminal of the neuron. Each vesicle can contain thousands of neurotransmitter molecules.

Neurotransmitters relay messages or signals from one nerve cell to the next nerve, muscle or gland cell by traveling between cells and attaching to specific receptors on target cells. These signals contain an electrical charge. As the signal travels along a nerve cell, its electrical charge causes the nerve cell membrane at the edge of the cell and the membrane of the synaptic vesicles to fuse together. This fusion of the membranes releases the signal-carrying neurotransmitters from the axon terminal of the neuron into the synaptic junction, which is fluid-filled space between one nerve cell and the next target cell. The neurotransmitters relay the message across the synaptic junction to the target cell. 

Each neurotransmitter attaches to a specific matching receptor in the same way that a key can only fit into a matching lock. On attaching to the receptor, the neurotransmitter triggers an action or a change such as the release of hormones or a muscle contraction in the target cell.