Synonym
nerve cells, neurons, lat. : nerve, -i
Definition
Neurons are nerve cells and therefore part of the nervous system. They serve the
- Recording,
- Processing and
- Forwarding of information.
A nerve cell consists of a cell body (perikaryon or soma) and extensions. There are two types of extensions:
- Dendrites and
- Axons.
Physiology
Information is transmitted in the nerves in the form of action potentials. The basis for this are ion currents. At the nerve cell are – in a simplified scheme – the most important ions: The potassium concentration is high inside the cell (intracellular) and low outside the cell (extracellular), whereas the sodium concentration is low inside the cell and high outside the cell (extracellular).
This ion concentration is primarily achieved by an ion pump, which achieves sodium–potassium ATPase, which transports potassium ions into the cell and sodium ions out of the cell. If the cell membrane were now permeable for sodium and potassium, the ions would flow from the site of high to the site of low concentration. Thus, potassium would flow to extracellular, while sodium would flow to intracellular.
However, the membrane is not easily permeable for ions, but the permeability is regulated by specific channels. There are, for example, channels for potassium ions and channels for sodium ions. The ion current therefore depends on which channels are open and which are closed.
At rest – i.e. when they are not excited – the nerve cells have a resting membrane potential with clearly negative values: this resting potential is primarily generated by the constant outflow of potassium ions from the cell interior to the outside. This outflow is possible because certain potassium channels are open at rest. When the nerve cell is stimulated, mainly sodium channels open.
Through these channels an influx of positively charged sodium ions takes place, which makes the membrane potential more positive. If a certain threshold is reached, an action potential is created at the peak of which the membrane potential assumes positive values: By re-closing the sodium channels and re-opening the potassium channels, through which potassium ions leave the cell, the membrane potential quickly returns to its negative resting value after the action potential.
- Chemical and
- Electrical activity coded.
- Potassium and
- Sodium.
- About -70 mV.
- About +30 mV.
