What is the function of neurotransmitters

Structure and function of neurotransmitters

The nerve cells or neurons in our brain communicate with each other via contact points (so-called synapses). A single neuron can communicate with thousands of other neurons through the synapses. Two "languages" are used for signal transmission within and between neurons: an electrical language within the neuron or along the axon and a biochemical language between neurons. These biochemical transmitter substances are summarized under the term neurotransmitter. The task of the neurotransmitter is to transfer information between nerve cells (neurons). The scene of the action are the synapses - special contact points through which neurons are connected to one another.

This contact point is made up of three parts:

  • The presynaptic end head is located at the end of the nerve cell process (the axon end) of the signal-sending neuron
  • The signal-receiving neuron in turn has a so-called postsynaptic membrane
  • The synaptic gap, which is only a few thousandths of a millimeter wide, lies between these two structures
The electrical nerve impulse cannot jump this gap, but has to be transmitted from one neuron to the next, and that is the job of the neurotransmitter. Neurotransmitters are found as biochemical transmitter substances in tiny "bubbles" (the vesicles) in the presynaptic nerve endings. They are released by the electrical signal (action potential) from a neuron, which causes the vesicles to open. The neurotransmitters pour out of the open vesicles into the synaptic gap and migrate to the neuron behind the gap.

On the postsynaptic membrane of the signal-receiving neuron there are docking points (receptors) that work according to the lock and key principle (only one type of neurotransmitter can dock on one type of receptor, i.e. the shape must fit and no other neurotransmitters may already be on the receptor be attached). If a neurotransmitter binds to its receptor, this changes the permeability of the cell membrane of neuron B for certain electrically charged ions that are in the fluid outside the cell. The chemical signal is thus translated back into an electrical signal. At the end of the process, the neurotransmitter is either broken down or transported back to the starting neuron and taken up again through special openings in the cell wall. The latter process is known as "resumption".

Neurotransmitters can have a stimulating (so-called excitatory) or inhibiting (so-called inhibitory) effect. An exciting effect favors the development of an action potential and an inhibiting effect serves to prevent such a potential. This means that there is a possibility that certain inputs reinforce each other, or even that they are antagonistic and weaken each other or even wipe each other out. In addition, the neuron works according to the all-or-nothing principle: In order to trigger the action potential at all, the neuron also needs a certain threshold value of excitatory stimulation, i.e. if this value is not reached then no action potential is triggered.

There are also different types of neurotransmitters, i.e. different messenger substances that are intended for different types of information:

Acetylcholine

Acetylcholine is the most important neurotransmitter in the peripheral nervous system. This messenger substance mediates the transmission of excitation from the nerves to the muscles. In addition, acetylcholine plays a central role in the autonomic nervous system, which controls vital functions such as breathing, blood pressure, heartbeat, digestion and metabolism. It is also decisively involved in a wide variety of cognitive processes, e.g. in learning processes and memory formation. Alzheimer's disease provides evidence of this: As nerve cells die in the brain of those affected, there is a lack of acetylcholine, which is partly responsible for the decline in mental performance of patients.

Glutomat

This neurotransmitter is found primarily in the brain, where it is the most common excitatory neurotransmitter. Its receptors can be found in the most diverse areas of the brain. According to the current state of knowledge, glutamate is just as essential for the transmission of sensory perceptions and for controlling movement as it is for learning and memory. In Alzheimer's patients, both the release and the reuptake of the messenger substance are impaired. Resumption is particularly important here because too much glutamate can destroy the neurons.

GABA

GABA is the most important inhibitory neurotransmitter in the brain, it can be seen as something like the antagonist of glutamate. Medicines (such as sleep and sedatives such as benzodiazepines or diazepam aba.Valium) that imitate or intensify the effects of GABA at its docking site therefore typically have a depressant effect. Using this mechanism, they also have anti-anxiety effects and can reduce neuronal over-excitability during epileptic seizures.

Dopamine

Dopamine has a variety of functions, e.g. behavior, mood, attention, sleep, learning, motor activity, milk production. In the brains of Parkinson's patients, dopaminergic nerve cells die in a region of the brain that is responsible for regulating and controlling movements. This results in a dopamine deficiency and movement impulses can no longer be passed on properly. The result is the slowdown of the entire motor skills, which is typical of the disease. Due to the dwindling dopamine production, there is also a relative excess of other neurotransmitters such as acetylcholine and glutamate. This imbalance leads to the other two characteristic symptoms of Parkinson's disease, tremors and muscle stiffness. Psychosis and schizophrenia are openly associated with increased dopamine levels. For example, drugs that block a certain dopamine receptor improve symptoms in many cases. Cocaine and amphetamines also convey their intoxicating and stimulating effects via an increase in dopamine levels and can also lead to psychotic disorders as a result.

Norepinephrine

Norepinephrine is made from dopamine with the help of an enzyme and is primarily responsible for controlling the level of alertness and alertness. For example, patients with attention deficit disorder (ADHD) are treated with drugs that increase norepinephrine and dopamine levels in the central nervous system.

Serotonin

Serotonin has many effects in the brain, for example in the regulation of appetite, the sex drive, in dreaming, in the control of behavior and psychological well-being. This messenger is considered to be one of the central mood-makers. When we have high enough serotonin levels, the message is spread that we are satisfied, full, balanced and relaxed. In people with depression, the concentration of serotonin is often significantly reduced. Drugs for depression work against this problem by inhibiting the reuptake of the neurotransmitter in the nerve cells and thus increasing the serotonin level. The drug ecstasy also causes a strong increase in serotonin in the brain and thus triggers an intoxicating feeling of happiness. As soon as the effect wears off, however, the level rushes into the basement and with it the mood.