Synapses are specialized functional contacts that are located between excitable cells. They transmit and convert various signals. Synapses appear as thickenings at the ends of nerve fibers. With their help, nerve impulses propagate to neighboring cells. The main function of the synapse is the intercellular transmission of nerve impulses.
Classification and brief description
In accordance with the type of conduction of impulses, there are mixed, chemical and electrical synapses. Chemical transmission conducts the signal in one direction and amplifies it, and also depolarizes or hyperpolarizes the postsynaptic sphere. With the help of chemical synapses, plasticity in signal transmission increases, that is, a person improves memory and learning speed. There is no synaptic delay in electrical transmission, and the signal is conducted in two directions. Impulse transmission is independent of the action of the presynaptic membrane. In addition, electrical synapses are resistant to low temperatures, as well as some influences fromaspects of pharmacology. Synapses of mixed type have one feature. They conduct chemical and electrical signal transmission in parallel.
What is an electrical synapse?
Electrical synapses are intercellular formations, with the help of which the transmission of an excitation impulse is ensured. This process occurs due to the appearance of an electric current between two departments called presynaptic and postsynaptic. The nervous system of invertebrates has a large number of electrical synapses, while mammals have almost none. Together with this, electrical synapses are quite common among higher animals. They are mainly found in the heart, liver, muscles, as well as in the epithelium and glandular tissue. The synaptic gap in electrical synapses is much narrower than in chemical synapses. An important feature of this type of synapses is that there are peculiar bridges of protein molecules between pre- and postsynaptic membranes.
Important work of electrical type synapses
The properties of electrical synapses are as follows:
- quick action (much superior to activity in chemical-type synapses);
- weak trace effects (there is practically no summation from successive pulses);
- reliable transmission of excitation;
- high plasticity;
- transmission in one and both directions.
Structure features
StructureThe electrical impulse starts from the postsynaptic membrane. Next is a narrow synaptic cleft, which consists of transverse tubules, consisting of protein molecules. Behind the cleft is the presynaptic membrane. In the middle is a semicircular synaptic plaque. The oblong synaptic ending is the final element in the structure of the electrical synapse. Due to the presence of channels of protein molecules between pre- and postsynaptic cells, inorganic ions and the smallest molecules are able to move from one cell to another. Such a synapse has a very low electrical resistance. Under these conditions, the presynaptic current extends to the postsynaptic cells and practically does not fade away.
Specific functional properties
There are a number of unique functional features in electrical synapses. There is practically no synaptic delay. The impulse arrives at the presynaptic ending, after which the process of postsynaptic potential immediately begins. There is no interval between these actions. Electrical synapses provide the transmission of a single process - excitation. In synapses of this type, conduction is bilateral, despite the fact that, due to stereometric features, conduction in one direction is most efficient. Various factors (pharmacological, thermal, etc.) have virtually no effect on electrical type synapses.
How is excitation transmitted in electrical synapses? Process steps
Excitation conduction (PD) is the main work performed by the electrical synapse. The mechanism of this process in synapses is similar to AP in nerve fibers. When the conduction of excitation passes into the developmental stage, charge reversion begins in the presynaptic membrane. As a result, an electric current arises, which affects the postsynaptic membrane, irritates it and causes the generation of AP in it. The conduction of excitation in electrical synapses is a complex physiological process that proceeds in several stages. The presynaptic membrane transforms the electrical impulse into a chemical one, which, hitting the postsynaptic plate, again turns into an electrical signal.
Some defects in electrical synapses
Despite the fact that electrical synapses carry out a fairly simple process of excitation transfer, they have several large defects. And the stereotype of their actions is to blame for this. There is no possibility of directly transferring excitation to distant cells. Pre- and postsynaptic cells, which are connected by electrical-type synapses, are constantly in the same excitation. The appearance of inhibition is not possible. As a result of all the above deficiencies, the infant brain does not have a large number of electrical synapses, while in an adult there are quite a lot of them in the retina, brain stem and vestibular roots.
A similar, but already in a pathological form, the mechanism of conduction of excitation appears inthe result of diseases that are associated with degeneration of axon boundaries. As a result of this process, excitation "jumps" from one axon to another, which can lead to false sensations. For example, the appearance of a feeling of pain, despite the inactivity of peripheral pain receptors, may arise precisely because of the "jumps" of excitation.
