Electromechanical interface in muscles

Electromechanical interface is the cycle of consecutive processes beginning occurrence of potential of action on sarcolemma (a cellular membrane) and coming to an end retractive answer of a muscle.

I nfringement of sequence of processes of interface can lead to pathologies and even by a lethal outcome. The basic stages of this process can be tracked on fig. 10

In cardiac hystiocyte electromechanical interface goes in two steps: in the beginning the small entering stream of calcium activates membranes of sarcoplasmic reticulum, promoting the big emission of calcium from endocellular depot, and then as a result of this emission there is a reduction of sarcomere. The described two-level process of interface is proved experimentally. Experiences have shown, that: absence of a stream of calcium from the outside cells stops reduction of sarcomere, in conditions of a constancy of quantity of the calcium liberated from sarcoplasmic reticulum, change of amplitude of a stream of calcium leads to well correlating change of force of reduction. The stream of ions inside of a cell carries out thus two functions: forms long (200 msec) a plateau of potential of action of cardiac hystiocyte and participates during electromechanical interface.

In skeletal muscles potential of action short (2-3 msec) and the slow stream of ions of calcium in them is absent. In these cells the system of the cross-section tubules suitable directly to sarcomeres is strongly developed Т-, is close to z - to disks (fig. 11). Changes of potential of a membrane during depolarization through Т - system it is transferred in such cells directly to membrane of sarcoplasmic reticulum, causing fast liberation of ions and the furt her activation of reduction.

Electromyography - a method of electrophysiological diagnostics of defeats of the nervously-muscular system, consisting in registration of electric activity (biopotentials) of skeletal muscles.

Distinguish spontaneous electromyography, reflecting a condition of muscles in rest or at a muscular pressure , and also the caused muscles caused by electric stimulation or a nerve.

n eedle electrodes superficial electrodes

Devices for measurement of function of external breath. The device and a principle of work. Registration and the analysis of the given functional researches

BIOPHYSICAL BASES OF BREATH

During breath allocate three stages (stage): external breath, ventilation of lungs and diffusion of gases in them; transport 0₂ and С0₂ blood; the internal breath subdivided diffusion of gases in fabrics and cellular breath.

Gas exchange in lungs. In lungs the exchange of oxygen, carbonic gas, nitrogen between an organism and an environment is made. Owing to work muscles air cells exchange these gases with an atmosphere that provides a relative constancy of concentration 0₂ and especially С0₂ in a gas mix. The scheme of alveolar complex is represented on fig. 1.

Fig.1 Stages of the breath.

Gas exchange between an alveolar gas mix and blood of pulmonary capillaries occurs on a alveolar-capillary membrane (АCМ), which representing system with many membranes (fig. 2.). On this process do not render influence electric, osmotic and hydrostatic gradients. Long time the question on existence of active transport (secretion) of oxygen in lungs was studied. It is now conventional, that in an organism there are no systems of active transport of oxygen, some carbonic gas and nitrogen. Hence, gas exchange in lungs is carried out under action only one force – concentration gradient of each of gases on АCМ. Therefore mass transfer of gases occurs by Fick's to equation

Fig. 2.

F ig. 3. Schemes of alveolar-capillary and diffusion of gases in lungs:

a - layers « diffusion ways », b - the schematic image of an alveolus and a capillary, c - components of a -capillary membrane.

Using Fick's equation for a quantitative estimation of gas exchange through, it is expedient to replace a gradient of concentration with a gradient pressure and pressure of gases.

Partial pressure of gas is called such pressure of a component of a gas mix which it would render on an environment concluding it if one all volume given of this mix.

The maintenance of gas in a liquid can be characterized by a pressure. Pressure of gas in a liquid is such pressure of the given gas in a gas mix above this liquid which needs to be created for maintenance in its maintenance between a gas mix and a liquid, for any gas exchange between them. Units of dimensions of partial pressure are unit of dimension of pressure.

For a quantitative estimation of gradients on АСМ it is necessary to know it. On the scheme (fig. 4.) it is visible, that АСМ consists of two layers of cells: pulmonary capillaries and alveolar (respiratory), and also a membrane located between these layers. Promising thickness АСМ is very small - about 0,2 microns, but in the field of cellular kernels 10 microns reach. Except for the listed components, this system includes a surfactant.

Basis of surfactant is a double phospholipin layer similar of biological membranes. Surfactant continuously is updated owing to work of special cells alveolar epithelium, which allocate for a surface of an alveolus the smallest vesicles. In each of them the phospholipin layer densely packed, are opened on a surface of an alveolus. Due to surfactant diffusive way is slightly extended, that leads to decrease a concentration gradient on АCМ. However without surfactant breath in general would be impossible, as walls of an alveolus can stick with each other under action of the significant superficial tension inherent alveolar epitelium. Surfactant reduceses a superficial tension of alveolar walls. The factor of a superficial tension depends on thickness of the layer covering alveoluses: on a breath it is more thin and is equal to 0,05 N•m^-1, on an exhalation - more thickly also is equal 0,005-0,01 N•m^-1.

Concentration gradients of oxygen and carbonic gas on АСМ decrease at a pathology. They can decrease due to reduction of a difference of concentration of gases in alveoluses and pulmonary capillaries, and owing to increase in thickness of АСМ. The first reason - change of the gas environment, in which the person breathes (for example, at stay of the person in the rarefied air atmosphere - in mountains, in the plane), infringement of pulmonary breath (for example, at many illnesses of lungs, at the insufficient work of respiratory muscles leading restriction of movements of a thorax). The second reason - a pathology, for example, a hypostasis of lungs: the liquid leaves capillaries and accumulates in the intercellular environment (basal membrane), increases its thickness, reduces a concentration gradient of gases on АСМ. It is necessary to remember, that diffusion - function of a gradient, instead of a difference of concentration. Not knowing it, the doctor cannot penetrate in pathogenesis of some pathological conditions, including a hypostasis of lungs.

In normal conditions diffusive a way to Fick's equation,-1 a micron. On this distance difference of concentration 0₂ and С0₂ different. However mass transfer of both gases it is approximately identical. From Fick's equation it is visible, that the areas of gas exchange for 0₂ and С0₂ are identical, their identical mass transfer at distinction in gradients is possible due to different permeability АCМ for O₂ and carbonic gas. Getting ability of each gas is characterized by factor of diffusion.

Getting ability of oxygen allows it to pass through АCМ through the times filled by water. Carbonic gas as passes АCМ and, but it does it at 20-25 time more quickly, than oxygen. С0₂ has the best solubility. The high degree of solubility of carbonic gas is caused its small (close to zero) dipole by the moment. Molecule С0₂ non polar owing to the symmetric structure. It does not cooperate with the charged groups biomembrane components and easily gets through it. In an organism is not present substance which could compete to carbonic gas. Owing to the highest getting ability С0₂ participates in many processes providing regulation of breath, blood circulation and other functions of an organism. For an estimation of gas exchange in lungs it is necessary to know size of the diffusion area.

Owing to a significant surface of gas exchange full mass transfer 0₂ and С0₂ in lungs of the person it is carried out all for 0,1 with. At the same time in conditions of rest each of erythrocytes passes a pulmonary capillary (from the beginning up to the end) for 2-3 with.

At physical activity speed of a blood-groove increases, that results, to increase in a surface of the gas exchange falling unit в of contact of blood and an alveolar gas mix, and to shortening this contact. According to Fick's law, reduction of time should reduce volumes of gases, through АСМ. However it is fair only for very short-term (more shortly 0,1) gas exchange. When time of a blood-groove on pulmonary capillaries is reduced from 2-3 with (in rest) up to 0,1 with (at loading), mass transfer of gases in lungs does not decrease, but only increases. Here also the basic reserves of strengthening of gas exchange are concluded at physical activity as acceleration of a blood-groove in lungs up to the certain limits leads to the area of diffusion and at the same time does not reduce due to shortening time of contact of blood with alveoluses.

Told allows to understand, how much difficultly to estimate influence on gas exchange of the person of such sizes entering into the equation of Fick, as s and t. Therefore the original physical size - ability of lungs or factor of permeability for each of gases is entered.

Volume of the given gas, through АСМ all "breathing" surface of lungs during 1 minutes is called diffusive ability of lungs.

At quiet breath lungs of the person allocate in an atmosphere nearby 230см³ gases during 1 minutes.

At the heavy physical work demanding significant strengthening of breath, having got into the blood current on pulmonary capillaries, oxygen it is brought in all fabrics of an organism. Forms of this transport are various. First, 0₂ it is dissolved in plasma and, secondly, - contacts hemoglobin in. The given gas with that or other solvent.

Carbonic gas has(С0₂) The best solubility. Oxygen (02) is dissolved more poorly. In process of rise in temperature value of factor of solubility decreases. It gases differ from firm objects.