What are neurotransmitters?
Neurotransmitters are the body’s chemical messengers that are responsible to transmit signals between neurons, or between neurons and muscles.
The electric signals that travel down the axon get converted to chemical signals in the form of neurotransmitters. These are then released into the synaptic cleft between two neurons. A neurotransmitter can be either excitatory, inhibitory or modulatory.
Excitatory- When a neurotransmitter binds to a receptor, it might promote the generation of an action potential. Such neurotransmitters are called excitatory.
Inhibitory- Inhibitory neurotransmitters have the opposite effect on a neuron, i.e., they prevent the generation of an action potential.
Modulatory- Modulatory neurotransmitters regulate a population of neurons as they are not restricted in the synaptic cleft between just two neurons. Although they work slower than excitatory and inhibitory transmitters, they have the ability to affect a large number of neurons simultaneously.
Most neurotransmitters are either small amine molecules, amino acids, or neuropeptides. These chemical messengers and their interactions with different receptors regulate countless functions of the nervous system and control bodily functions.
Acetylcholine was the first neurotransmitter to be discovered. It plays a key role in not only the peripheral nervous system, but also the central nervous system. In the peripheral nervous system, it is released by motor neurons and neurons of the autonomic nervous system. In the central nervous system it helps in maintaining cognitive function.
The primary excitatory transmitter in the central nervous system is glutamate. Conversely, its derivative γ-aminobutyric acid (GABA) is a major inhibitory transmitter, while another inhibitory neurotransmitter is glycine, which is mainly found in the spinal cord.
Many neuromodulators, including dopamine, are monoamines. Due to the several dopamine pathways in the brain, this neurotransmitter is involved in many functions, such as motor control, reward and reinforcement, and motivation.
Noradrenaline (or norepinephrine) is another monoamine, and is the primary neurotransmitter in the sympathetic nervous system where it works on the activity of various organs in the body to control blood pressure, heart rate, liver function and many other functions.
Serotonin (another monoamine) is another common neurotransmitter that affects neurons that project to various parts of the nervous system. As a result, serotonin is involved in functions such as sleep, memory, appetite, mood and others. Serotonin is produced in the gastrointestinal tract in response to food.
Histamine, the last of the major monoamines, plays a role in metabolism, temperature control, regulating various hormones, and controlling the sleep-wake cycle, amongst other functions.
Queensland Brain Institute, The University of Queensland, Australia. What are neurotransmitters? https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters