The synapse is the structure having specially, special appointment and capable to provide intercellular transmission of messages in total of electric and (or) chemical character.
What is a synapse in biology?
Structural units of the central nervous system, namely neurons, connect in functional systems and form a whole by means of special structural formations, that is synapses.
The fact that the synapse (synapsis) is in a special way organized area, as a rule, of soprikosnovenny interaction of neurons, at the same time allowing to reproduce broadcast of nervous impulses, but only in the unilateral direction follows from all aforesaid.Thanks to direct support of synapses there is possible a transfer of information data from receptor cages on dendrites of sensitively susceptible neurons, from one nervous cage on other, from a nervous cage on fiber of a skeletal muscle, ferruterous and other effector cages. By means of synapses I have chances practically to be made exciting or brake impacts on cages, to become more active or restrain in overwhelming sense their metabolism and other functions.
The Mezhneyronalny functional systems of neurons, that is synapses can form:
1) all shoots of associative neurons;
2) axons of sensitive neurons;
3) dendrites of motor neurons.
Structure of a synapse
All synapses have property to possess the identical building in which scientists, as a rule, learned to distinguish presynaptic (by definition the nervous termination of one of the contacting cages is called as it) and postsynaptic (according to terminology from a biology course under this concept perceive that part of other cage to which the synoptic termination of the first cage) membranes goes and the synoptic crack dividing them (it is that other, as space between membranes of two cages). It should be noted that the presynaptic membrane is most often created by an extreme branch of an axon (in more exceptional cases the presynaptic membrane can be formed by a body or a dendrite) one neuron, and a postsynaptic membrane - a body or a dendrite of other neuron (in more exceptional cases - an axon).
One of important components of a synapse are bubbles (vesicles) which are located in a shoot before a presynaptic membrane. They contain physiologically active agents - mediators (neurotransmitters).
The excitement which is taking place on an axon intensifies stimulation of emission of a mediator from a bubble, and, having appeared in a synoptic crack, as we know, the mediator, in turn, directly influences a postsynaptic membrane of a dendrite, causing in it thus excitement emergence.
The impulse by means of carrying out through a synapse can be carried out only in one direction, namely in the direction from a presynaptic cover on postsynaptic.
In this section there is one more very important concept - a synoptic delay. It is expressed available lower speed of passing of a nervous impulse directly through a synapse if to compare indicators of this speed to indicators of speed of passing of a nervous impulse on nervous fiber.
Except presented in the description before (chemical synapses), exist as well electric synapses which by the nature, as a rule, are most characteristic not only of heart, smooth muscles, sekretorny cages but also take place to be in central nervous system, in some kernels of a trunk of a brain. Important aspect of electric synapses is the following sign: in comparison with chemical synapses, in electric synapses a crack already and an electric impulse are carried out through konneksona (this definition is meant as special channels of the proteinaceous nature) to both parties without synoptic delay.
Classification of synapses
According to modern scientific publications it is quite possible to classify synapses, as a rule, depending on their location (i.e. by what parts of the contacting nervous cages formed it), according to productive effect and according to a possible method of signaling. So, depending on location distinguish the following special structural formations:
- Aksosomaticheskiye (in this case the synapses formed between an axon of one cage and a body another are meant);
- Aksodendritnye (in this case the synapses formed between an axon of one cage and a dendrite another are meant);
- Aksoaksonnye (in this case the synapses formed between two axons are meant);
- Dendrosomaticheskiye (in this case the synapses formed between a dendrite of one cage and a body another are meant);
- Dendrodendritnye (in this case the synapses formed between two dendrites are meant).
On productive effect learned to distinguish the following special structural formations:
- exciting;
On a way to a possible method of direct signaling began to distinguish the subsequent functional systems:
- electric;
- chemical (more they are widespread in the central nervous system; it is worth noticing that transfer of a nervous impulse in this case happens as it is described above, by means of a mediator, that is the intermediary);
- electrochemical (this concept is meant as synapses which have ability to combine characteristics of the structure of the first two above-stated types).
What properties chemical synapses are capable to have?Chemical synapses in absolute degree are capable to possession of the following corresponding qualities, namely:
- Limited implementation of unilateral carrying out signal transmission, as a rule, only from a presynaptic cover to postsynaptic.
- The slowed-down signal transmission which, first of all, is caused by a synoptic delay in signal transmission from one section on other. The above-stated delay is excited by temporary expenses on processes of emission of a mediator, its diffusions to a postsynaptic membrane and so continuing.
- The ability to interaction of synoptic processes which is characterized by strengthening of effects of irritation before reflex reaction, this result from the signals coming to a synapse.
- Noticeable transformation of a rhythm of vozbuzhdeniye.
- Low speed of course of elementary physiological reactions and considerably increased fatigue of synapses. Synapses have every chance to carry out from fifty to hundred nervous impulses in time frames the size in one second. Thus the fact that in case nervous fibers are almost not tired, then in synapses the overfatigue forms the development extremely instantly turns out. The above process is the result of exhaustion of the available reserves of a mediator, energy resources, formations of strong depolarization of a postsynaptic cover and other factors.
- Considerably the increased susceptibility of synapses to influence of biologically active operating elements, pharmaceutical substances of medicinal purpose and poisons.
- Quality characteristics of simplification and depression of synoptic transfer. For example, simplification of synoptic transfer has certain potential to the real existence in case nervous impulses are enlisted to a synapse by means of the short temporary period serially, namely is rather frequent.