Electrical synapses and their features
Synapses are specializedfunctional contacts that are located between excitable cells. They transmit and convert various signals. Synapses appear as thickening at the ends of nerve fibers. With their help, nerve impulses spread to neighboring cells. The main function of the synapse is the intercellular transfer of nerve impulses.
Classification and brief description
In accordance with the type of impulsesthere are mixed, chemical and electrical synapses. A chemical transmission carries a signal to one side and amplifies it, and also depolarizes or hyperpolarizes the postsynaptic sphere. With the help of chemical synapses, plasticity increases in the transmission of signals, that is, the person improves memory and speed of training. In the electric transmission there is no synaptic delay, and the signal is conducted in two directions. Transmission of the pulse is independent of the effect of the presynaptic membrane. In addition, electrical synapses are resistant to low temperatures, as well as some effects from pharmacology. Synapses of mixed type have one feature. They conduct a parallel chemical and electrical signal transmission.
What is an electrical synapse?
Electrical synapses are intercellularthe formation, by means of which the transmission of the excitation pulse is ensured. This process occurs due to the appearance of an electric current between two sections called presynaptic and postsynaptic. The nervous system of invertebrates has a large number of electrical synapses, whereas in mammals there are practically 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. Synaptic cleft in electrical synapses is much narrower than in chemical ones. An important feature of this type of synapse is that between the pre- and postsynaptic membranes, there are original bridges of protein molecules.
Important work of synapses of electrical type
The properties of electrical synapses are as follows:
- rapid action (much superior to activity in synapses of chemical type);
- weak trace effects (summation from consecutive pulses is practically nonexistent);
- reliable transmission of stimulation;
- high plasticity;
- transfer to one and both sides.
Features of the structure
The structure of the electric pulse begins withpostsynaptic membrane. Next passes a narrow synaptic cleft, which consists of transverse tubules, consisting of protein molecules. Presynaptic membrane is located behind the slit. 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 from protein molecules between pre- and postsynaptic cells, inorganic ions and the smallest molecules are able to transfer from one cell to another. Such a synapse has very low electrical resistance. Under these conditions, the presynaptic current extends to the postsynaptic cells and practically does not die out.
Specific functional properties
In electrical synapses there are a number ofunique functional features. There is practically no synaptic delay. The impulse comes to the presynaptic ending, after which the process of the postsynaptic potential immediately begins. The interval between these actions is absent. Electrical synapses provide the transmission of a single process-excitation. In synapses of this type, carrying out is two-sided, in spite of the fact that due to stereometric features, conducting in one direction is most effective. Various factors (pharmacological, thermal, etc.) have practically no effect on synapses of electrical type.
How is excitement transmitted in electrical synapses? Stages of the process
Carrying out excitement (PD) is the main work,which is performed by the electric synapse. The mechanism of this process in synapses is similar to PD in nerve fibers. When the excitation is transferred to the stage of development, a charge reversal begins in the presynaptic membrane. As a result, an electric current arises that affects the postsynaptic membrane, irritates it and causes it to generate PD. Carrying out excitation in electrical synapses is a complex physiological process that takes place in several stages. The presynaptic membrane transforms the electrical impulse into a chemical pulse, which, once it hits the postsynaptic plate, again turns into an electrical signal.
Some defects in the work of electrical synapses
Despite the fact that the electrical synapsesthey carry out a rather simple process of excitation transfer, they have several large defects. And this is the fault of the stereotype of their action. There is no possibility of directly transferring excitation to distant cells. Pre- and postsynaptic cells, which are connected by synapses of electrical type, are constantly in the same excitation. The appearance of inhibition is impossible. As a result of all the above deficiencies, there is not a large number of electrical synapses in the brain of the infant, whereas in the adult human there are quite a lot of them in the retina of the eyes, the brainstem and the roots of the vestibular apparatus.
Similar, but already in a pathological formthe mechanism of excitation is due to diseases that are associated with degeneration of the 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 sense of pain, despite the inactivity of peripheral pain receptors, can arise precisely because of the "jumps" of excitation.