Functionality of chemical synapses

Whenever a nerve cell sends a signal to a muscle, gland or other nerve cell, the transmission takes place via the synaptic gap, which is only about 20-30 nanometers wide. The long extensions of the nerve cells (also called “axons”) conduct the nerve impulse (i.e. the “action potential“) from the center of the nerve cell to the target cell. The synaptic gap is located between the axon and the target cell (for example a muscle cell).

At the presynaptic membrane – i.e. the membrane located at the end of the axon – so-called synaptic vesicles pour a neurotransmitter into the synaptic gap. At the other end of the synaptic cleft, in our example, is a muscle cell with a postsynaptic membrane, i.e. a membrane located after the synaptic cleft. This membrane contains receptors that transmit the action potential as soon as the neurotransmitter binds to it.

A well-known neurotransmitter is for example dopamine (known from the drug cocaine!). As soon as sufficient action potentials are formed at the postsynaptic membrane, the muscle cell reacts and contracts. The same is true for glandular cells, or other nerve cells. This signal transmission occurs within a few milliseconds. In the case of electrical synapses, the transmission takes place directly via electrical impulses without chemical modeling.

Neurotransmitter

Neurotransmitters are messenger substances that transmit a signal from one nerve cell to another. The forwarded signal can be either an activation or an inhibition of the following nerve cell. This depends on which messenger substance is involved and which receptors are present at the postsynaptic membrane of the second nerve cell.

There are many different types of neurotransmitters that can act in both the central and peripheral nervous systems. Acetylcholine is a very important messenger substance of the human body. It serves as a transmitter at many synapses, both in the central nervous system, which includes the brain and spinal cord, and in the peripheral nervous system, which includes the entire nervous system except the central one.

In the peripheral nervous system, acetylcholine has two important functions. On the one hand, it is the messenger substance that transmits excitation from the nerve cell to the muscle. On the other hand, it serves to transfer signals in the autonomic nervous system, which controls functions such as digestion or sweat secretion, i.e. processes that we cannot consciously control.Dopamine is a transmitter that plays a role mainly in the central nervous system.

On the one hand, it is involved in the initiation and coordination of movement. The loss of certain dopamine-producing nerve cells can be seen, for example, in the form of Parkinson’s disease (Morbus Parkinson). It also has an important function in the development of motivation and drive.

In conjunction with norepinephrine, it also has a happiness enhancing effect. It is therefore also known as one of the “happiness hormones“. In the rest of the body it has a similar effect to adrenaline or noradrenaline, for example by increasing blood pressure. In certain doses it increases the blood flow to the abdominal organs, including the kidneys.