The Excitation transmission from cell to cell - also from nerve cell to nerve cell - happens via synapses. These are junctions between two nerve cells or between nerve cells and other tissue cells that specialize in signal transmission and reception.The signal is usually transmitted via so-called messenger substances (neurotransmitters); only when the transmission is from muscle cell to muscle cell can the stimulus be transmitted via an electrical potential. The transmission of excitation is also known as ‘‘ ‘Transmission‘ ‘‘.
What is excitation transmission?The transmission of excitation from cell to cell - also from nerve cell to nerve cell - takes place via synapses.
The enormous number of cells in the human body must be able to communicate with one another or be able to receive instructions in order to carry out a certain behavior of the organism, e.g. B. muscle contractions to produce. This versatile process takes place via a differentiated transmission of excitation.
Most of the impulse transmission is transmitted to the synapses through activation and release of transmitter substances. This forwarding and, if necessary, the distribution of action potentials to several recipients is usually carried out chemically via chemical synapses at which the messenger substances or neurotransmitters are transmitted to the recipient cell.
The end knobs of the synapse have no direct contact with the target cell, but are separated from it by the synaptic gap in the order of 20 to 50 nanometers. This offers the possibility of changing or inhibiting the transmitter substances in the synaptic gap that they have to overcome, i.e. converting them into inactive substances. The action potential is then collected again.
Muscle cells can also be connected to one another with electrical synapses. In this case, action potentials are transferred in the form of electrical impulses directly to the next muscle cell or even to many cells at the same time.
Function & task
Humans have around 86 billion nerve cells. A large number of control loops and many deliberate and targeted actions, but also life-sustaining reactions to external threats, must be controlled. The extraordinarily large number of body cells must be made to work together in a coordinated manner in order to implement the required and desired reactions of the entire organism.
In order to fulfill the tasks, the body is traversed by a dense network of nerves, which on the one hand report sensory information from all body regions to the brain and on the other hand allow the brain to send instructions to organs and muscles. The upright gait alone sets millions of nerve cells into action for the coordinated sequence of movements, which simultaneously and constantly check, compare and process the position of the limbs, the direction of gravity, the forward speed and much more in the brain in order to generate contraction and relaxation signals in real time to send certain muscle groups.
A unique system of excitation transmissions or transmissions is available to the body to fulfill these tasks. As a rule, a signal must be transmitted from nerve cell to nerve cell or from nerve cell to a muscle cell or another tissue cell. In some cases, signal transmission between muscle cells is also necessary. Usually an electrical action potential is passed on electrically within a nerve cell and, when it reaches the contact point (synapse) to the next nerve cell, is converted again into the release of specific messenger substances or neurotransmitters. The neurotransmitter has to overcome the synaptic gap and, after being received by the recipient cell, is converted back into the electrical impulse and passed on.
The detour of signal transmission via the chemical intermediate phases is important, as specific neurotransmitters can only dock on specific receptors and the signals become selective, which would not be possible with purely electrical signals. It would trigger a wild chaos of reactions.
Another important point is that the messenger substances can be changed or even inhibited during the passage through the synaptic gap, which can be tantamount to removing the action potential.
Only the signal transmission between muscle cells can take place purely electrically through electrical synapses. In this case, so-called gap junctions enable electrical signals to be transmitted directly from cytoplasm to cytoplasm. With muscle cells - especially heart muscle cells - this has the advantage that many cells can be synchronized for a contraction over greater distances.
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Illnesses & ailments
The great advantages of converting electrical action potentials into specific neurotransmitters, which enables simultaneous - and necessary - selective signal transmission, also harbors the risk of harmful intervention and attack possibilities.
Basically there is the possibility that synapses are overexcited or inhibited. This means that poisons or drugs can cause cramps or paralysis in neuromuscular synapses. If synapses in the CNS are influenced by poisons or drugs, there are mild to severe psychological effects. It can cause anxiety, pain, fatigue, or irritability for no apparent reason at first.
There are several ways of influencing the transmission. For example, the botulinum toxin inhibits the vesicle emptying into the synaptic gap, so that no neurotransmitter is transmitted and this leads to muscle paralysis. The opposite effect is caused by the poison of the black widow. The vesicles are completely emptied, so that the synaptic gap is literally flooded with neurotransmitters, which leads to severe muscle cramps. Similar symptoms as with botulinum toxin occur with substances that prevent the receptor cell from taking up the messenger substances again.
There are also other possibilities to prevent or impair the transmission of excitation. For example, some substances can occupy the receptors of a certain neurotransmitter and thereby trigger symptoms of paralysis.