How fast does a nerve impulse move
The nerve cells
Structure of a nerve cell
Hundreds of billions of nerve cells in the human body enable signals to be transmitted from the sensory organs to the brain and from the brain to organs and body peripherals. The structure and function of a nerve cell are as complex as they are fascinating.
There are many different types of nerve cells (neurons) that have developed specializations in form and function. However, they all share certain similarities.
Each neuron has a relatively large cell body (soma). The most obvious difference to other cells, however, are the long processes that arise from the cell body: the dendrites and axons.
The dendrites receive signals from other cells and pass them on to the cell body. The axons conduct the impulses from the soma to their endings, where the so-called end knobs are located.
Electricity in the body: transmission of signals within the cell
The signal that arrives from the dendrites via the cell body and the axon to the terminal knobs of a nerve cell is passed on in the form of an electrical impulse.
As with any living cell, the interior of a nerve cell is more negatively charged than its surroundings. This is due to the difference in concentration of charged particles (salt ions) between inside and outside.
What is special about nerve cells, however, is that they can use this difference in concentration (an electrical potential) to transmit an electrical impulse.
A special structure of the nerve cell membrane (the presence of special ion channels and pumps) enables electrical currents to flow through the membrane and thus signals can travel along the cell.
From one cell to the next: the processes at the synapse
For medicine, a certain station in the signal transmission is of particular interest: the exchange of information from nerve cell to nerve cell at the so-called synapse. In many diseases such as Parkinson's or depression, these switching points are out of balance.
Nerve cells are (as a rule) not connected to one another in an electrically conductive manner. That means: In order to be able to transfer information from one cell to the next, a gap has to be overcome. This gap is called the synaptic gap. A synapse consists of the axon terminal of the sender cell, the dendrite of the recipient cell and the synaptic gap between them.
In the axon terminal there are small bubbles (vesicles) that contain chemical messengers (neurotransmitters). When an electrical impulse arrives in the terminal button, the vesicles fuse with the cell membrane and the messenger substances are released into the synaptic cleft. The electrical signal becomes a chemical one.
Special docking points (receptor molecules) for the messenger substances are located on the cell membrane of the recipient cell. When a transmitter binds to a receptor molecule, an electrical signal is triggered again in the recipient cell, which can propagate along the cell. This is how nerve impulses are passed on from cell to cell. Like dominoes, one signal triggers the next.
Intervening in the balance: drugs in the brain
A system that is as complex as the processes at the synapse is of course sensitive to external influences. Psychoactive substances can intervene at different points in the process.
These include various intoxicants (cocaine, ecstasy), drugs (antidepressants, sedatives) but also so-called luxury goods such as coffee and cigarettes. This can have different effects depending on the substance.
For example, some substances cause the neurotransmitters to stay longer in the synaptic cleft (by inhibiting their breakdown or re-absorption into the sender cell). This is desirable for some diseases, such as depression, because the concentration of certain neurotransmitters is too low there.
The abuse of intoxicants, on the other hand, can lead to overstimulation and thus to psychosis and of course addiction.
Nerve cells in motion: learning and memory
Perhaps one of the most important functions of nerve cells for our self-image is the ability to learn. The synapses also play a decisive role in this.
Our memory is assigned to a specific area of the brain, the hippocampus. During learning processes, there are functional changes at certain synapses, which lead to the electrical responses in the recipient cells becoming stronger. Frequent repetition, i.e. using the synapse, strengthens the connection between the two cells (also by creating new connections).
You can think of it as a beaten path through the forest: the more it is used, the more easily accessible it becomes - it is easier to find it and it is always easier to move around on it. But it can just as well grow over again when it is not needed.
This also happens in the brain - learning new things creates new connections; if they are not needed, they are also broken down again. So: only those who keep their nerve cells going will remain mentally flexible!
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