Function
Nerve cells are able to process input signals and transmit new signals based on them. A distinction is made between excitatory and inhibitory nerve cells. Exciting nerve cells increase the probability of an action potential, while inhibiting ones reduce it.
Whether a nerve cell excites or not depends basically on the neurotransmitter that this cell emits. Typical excitatory neurotransmitters are glutamate and acetylcholine, while GABA and glycine inhibit. Other neurotransmitters such as dopamine can either excite or inhibit depending on the type of receptor on the target cell.
The excitatory and inhibitory signals that reach the nerve cells are spatially and temporally integrated and “converted” into action potentials. Thus, a single signal that reaches a nerve cell does not necessarily have an effect; unlike in muscle cells, where each signal leads to an opening of ion channels and thus to a contraction of the muscle cell.If, on the other hand, the excitation of the nerve cell is supra-threshold, the all-or-nothing principle applies: the triggered action potential always has the same amplitude. A modulation of the activity can therefore only take place via the frequency of the action potentials, not via their intensity. The situation is different with signals emanating from axons of other nerve cells: here, temporally accumulated excitation can lead to a higher sensitivity of the cell to this signal. This phenomenon is known as long-term potentiation and is, for example, partly responsible for learning processes and memory formation.
Tasks of the nerve cell
As the eponymous cells of the nervous system, neurons play a decisive role in sensory and motor functions, the coordination of vegetative functions and cognitive performance. The nervous system can be functionally subdivided: the somatic nervous system performs tasks that are important for interaction with the environment. These include the innervation of skeletal muscles and the perception of external stimuli, for example through the sense of sight.
The autonomic nervous system coordinates the function of internal organs and adapts their activity to environmental stimuli. It can be further subdivided into the symphatic, parasympathetic and enteric nervous system. The sympathetic nervous system has functions which are necessary in the sense of a fight-or-flight reaction, i.e. a stress reaction to environmental stimuli.
It increases heart strength and blood pressure, dilates the bronchi and reduces the activity of the gastrointestinal tract. Conversely, an activation of the parasympathetic nervous system leads to an activation of the gastrointestinal tract (rest and digest) and a reduction of blood pressure and heart work. The enteric nervous system, on the other hand, works primarily independently of the central nervous system and coordinates functions within the gastrointestinal tract and is modulated by the symphatic and parasympathetic nervous systems.
The central nervous system, on the other hand, can be divided into core areas with motor, sensory, sympathetic, parasympathetic and higher cognitive functions, which can be found at different locations in the brain or spinal cord. A nerve cell has many dendrites, which are a kind of connecting cable to other nerve cells in order to communicate with them.
- Nerve cell
- Dendrite
Besides the neurites, which only lead in one direction, there are other extensions of the nerve cell, the dendrites (= Greek tree).
The dendrites are much shorter than the long neurite and are located near the cell body (perikaryon). Usually they are present in the form of a large dendrite tree. Their task is to receive stimuli from other nerve cells.
The connecting element, the “interface” between individual neurons is called a synapse.
- Nerve ending (Axon)
- Messenger substances, e.g. dopamine
- Other nerve ending (dendrite)
Here, the end of the long nerve cell process (axon end) of one neuron encounters the dendrite tree of another neuron. The interaction between the two takes place through a chemical transmitter, a neurotransmitter; the process is thus similar to an “electrochemical coupling”. One neuron can be linked to up to 10,000 others in this way, resulting in a total number of synapses of an estimated one trillion (a 1 with 15 zeros!)! This interconnection of neurons leads to a complex neural network – or several functionally distinguishable networks.