Definition – What is a neurotransmitter?
The human brain consists of an almost unimaginable number of cells. An estimated 100 billion neurons, which carry out the actual thinking work, and once again the same number of so-called glial cells, which support the neurons in their work, form the organ that makes us humans something special in this world. To enable these nerve cells to communicate with each other, a complex system of messenger substances, the neurotransmitters, has developed over the course of evolution.
These are a little more than two dozen chemical compounds, some of them very different, which can be divided into different groups according to various aspects. The most common classification is based on their chemical structure. For example, there is a small group of soluble gases, to which carbon monoxide (CO) and nitrogen monoxide (NO) belong, but also a large group of amino acids, the building blocks of proteins, which act as neurotransmitters.
Proteins themselves also form a group of neurotransmitters. It is of enormous importance that this extensive system of messenger substances in the brain remains in balance, since a lack or surplus of neurotransmitters has devastating consequences for the functioning of our nervous system. Depending on the part of the brain in which the imbalance occurs, this can affect both our mental and physical health.
Diseases such as Parkinson’s disease, schizophrenia and even depression are at least partly the result of changes in brain chemistry. On the other hand, however, we can also use our knowledge of the messenger substances of the nervous system to treat precisely these diseases. Incidentally, neurotransmitters are by no means the same as hormones. While hormones are released into the bloodstream and reach their target organs via the circulatory system, neurotransmitters are only used for communication within the nervous system.
Tasks of the neurotransmitters
Within individual nerve cells (neurons), which in humans can be more than one meter long, the information is transmitted via electrical voltage, comparable to power cables. However, this conduction is regularly interrupted when the information is to be passed on from one neuron to another. This is where the chemical component of information transmission in the brain by means of neurotransmitters comes into play.
The contact points between neurons where the chemical information transfer takes place are called synapses. About one trillion of them exist in our brain alone. Applied to the number of neurons themselves, this means that each individual nerve cell is connected to 1000 other nerve cells on average.
The task of the neurotransmitters is therefore to bridge the interruption of the electrical impulse between two neurons. This is done by the impulse arriving at the synapse leading to the release of neurotransmitters from their storage vesicles of Neuron A into the synaptic cleft. In this gap between the neurons, which is only a few nanometers wide, the messenger substances diffuse to their corresponding receptors on Neuron B.
Here, the chemical information is converted back into electrical information. The effect that each individual neurotransmitter achieves in this process depends very much on the brain region in which this mechanism takes place. As a result, a particular neurotransmitter performs a variety of tasks in different areas of the brain. It is important to know that neurotransmitters do not always have an excitatory effect on the downstream nerve cell, but can also have an inhibitory effect on the electrical transmission of information.
