Synapses are specialized functional contacts that are located between excitable cells. They transmit and transform various signals. Synapses appear in the form of thickenings at the ends of nerve fibers. With their help, nerve impulses spread 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 pulses, there are mixed, chemical and electrical synapses. Chemical transmission conducts the signal in one direction and amplifies it, as well as depolarizes or hyperpolarizes the postsynaptic sphere. With the help of chemical synapses, the plasticity in signal transmission increases, that is, a person improves memory and learning speed. There is no synaptic delay in the electrical transmission, and the signal is conducted in two directions. Impulse transmission is independent of the effects of the presynaptic membrane. In addition, electrical synapses are resistant to low temperatures, as well as some effects from pharmacology. Mixed-type synapses have one feature. They simultaneously conduct chemical and electrical signal transmission.
What is an electrical synapse?
Electrical synapses are intercellular formations, with the help of which the transmission of an excitation pulse 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 ones. An important feature of this type of synapse is that between the pre- and postsynaptic membranes there are peculiar bridges of protein molecules.
Important work of electrical type synapses
The properties of electrical synapses are as follows:
- fast action (far superior to activity in chemical type synapses);
- weak trace effects (there is practically no summation from successive pulses);
- reliable transmission of excitation;
- high ductility;
- one-way and two-way transfer.
Structure Features
The structure of the electrical impulse begins with the postsynaptic membrane. Next is a narrow synaptic cleft, which consists of transverse tubules, consisting of protein molecules. A presynaptic membrane is located behind the gap. 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 a very low electrical resistance. Under these conditions, the presynaptic current extends to postsynaptic cells and practically does not die out.
Specific functional properties
There are a number of unique functionalities in electrical synapses. There is practically no synaptic delay. The impulse comes to a 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, conducting is two-way, despite 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 the electrical type.
How is excitation transmitted at electrical synapses? Process steps
Carrying out excitation (PD) is the main work that the electrical synapse performs. The mechanism of this process in synapses is similar to PD in nerve fibers. When the excitation proceeds to the developmental stage, the charge reverses in the presynaptic membrane. As a result, an electric current arises that affects the postsynaptic membrane, irritates it, and causes the generation of PD in it. Carrying out 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, once on the postsynaptic plate, again turns into an electrical signal.
Some defects in the operation of electrical synapses
Despite the fact that electrical synapses carry out a rather simple process of transferring excitation, they have several large defects. And the stereotype of their action is to blame. There is no way to directly transfer excitation to distant cells. Pre- and postsynaptic cells, which are connected by synapses of the electrical type, are constantly in the same excitation. The appearance of braking is not possible. As a result of all the above shortcomings, the baby’s brain does not have a large number of electrical synapses, while an adult has quite a few of them in the retina, brain stem and roots of the vestibular apparatus.
A similar, but already pathological form of the mechanism of excitation appears as a result of 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 feeling of pain, despite the inaction of peripheral pain receptors, can occur precisely because of “jumps” of excitation.