Synapses and neurotransmitters are both key components of the central nervous system’s chemical communication network, responsible for relaying messages between nerve cells, or neurons. Figuratively speaking, the neurotransmitter is the messenger and the synapse is the pathway traveled by the messenger. Physically, both synapses and neurotransmitters are located on the synaptic cleft, which is the space between the end of the neuron sending a message and the beginning of the neuron receiving the communication.
When an animal or person gleans information from a sensory organ or brain impulse, it uses synapses and neurotransmitters to share that information, whether beneficial or threatening, with multiple nerve cells, which can then send orders to muscles, allowing the physical body to react to what is seen, heard or thought. The entire process can take less than one millionth of a second. Every neuron has access to at least 1,000 pathways, or synapses.
Once data from the brain or senses are sent to a nerve cell, that nerve cell releases neurotransmitters from its terminal end, formally called an endfoot. One endfoot might release 2,000 to 5,000 molecules of neurotransmitters at a time, depending on how much calcium is present. Until release, neurotransmitters are stored in circular membranous enclosures, known as vesicles, on the endfoot. After release, neurotransmitters travel the synapses by means of diffusion to reach the membrane of the next nerve cell, where they can be reused and sent to other neurons or allowed to disintegrate.
Synapses participate in both electrical and chemical communication in the nervous system. While synapses and neurotransmitters work together for chemical messaging, electrical communication does not rely on neurotransmitters. During electrical messages, which are generally used exclusively for brain or eye activity, nerve cells send ionic currents across synapses to one another. In such instances, these ionic currents become the messengers, thereby replacing the chemicals known as neurotransmitters. Neurotransmitters are used in communication everywhere else in the body.
There are two types of synapses and neurotransmitters. Synapses can be symmetrical or asymmetrical, while neurotransmitters can be excitatory, like glutamate, or inhibitory, like gamma-aminobutyric acid (GABA). A few rare neurotransmitters, such as dopamine, are both excitatory and inhibitory.
Excitatory neurotransmitters are released from round vesicles and travel along asymmetrical synapses. Inhibitory neurotransmitters are released from flat vesicles and travel symmetrical synapses. Examples of neurotransmitters include acetylcholine, which influences muscles action, and dopamine, which influences sensory perception, mental focus, and mood. Other neurotransmitters include norepinepherine, which helps sleep patterns, and serotonin, which helps with cognition, appetite and dreams.