Физиология и этология животных теоретический курс (возбудимые ткани) = Physiology and ethology of Animals theoretical course (excitable tissues). Учеб

E. D. Sotnikova, E. V. Kulikov, V. M. Byakhova

PHYSIOLOGY AND ETHOLOGY OF ANIMALS:

THEORETICAL COURSE

(EXCITABLE TISSUES)

Е. Д. Сотникова, Е. В. Куликов, В. М. Бяхова

ФИЗИОЛОГИЯ И ЭТОЛОГИЯ ЖИВОТНЫХ: ТЕОРЕТИЧЕСКИЙ КУРС (ВОЗБУДИМЫЕ ТКАНИ)

Москва Российский университет дружбы народов

2018

1.Introduction to Physiology

1.1.Definition of physiology as a science, its sections,

goals and tasks

Originally the term physiology (from the Greek physis - nature and logos - teaching) denoted the science of the fauna and flora world in general. With the accumulation of knowledge (XVI-XVIII cent.), independent biological disciplines emerged from physiology: zoology, botany, anatomy. The task of the latter included not only the description of the structure of the body of animals, but also the study of its functions. Only in the XIX century branch of anatomy, studying the processes of life, was singled out as an independent science, behind which the former name - physiology - was preserved.

Physiology is a biological science that studies the vital processes of the organism and its constituent parts (cells and subcellular structures, tissues, organs, organ systems) in their unity and interrelation with the environment.

The main tasks of physiology:

1.Study of the laws of life processes (metabolism, respiration, nutrition, movement, etc.) at different structural levels;

2.Study of the mechanisms ensuring the interaction of different parts of the body and the whole organism with the external environment;

3.Study of qualitative differences in physiological functions in animals at different developmental levels or inhabiting different environmental conditions;

4.Study of the formation of physiological functions, their formation at different stages of individual development.

5.Study of qualitative differences in functional processes in different animal species.

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Thus, a number of independent subdisciplines are distinguished in the physiology of animals.

General physiology studies the patterns of life processes of all living organisms (the thermodynamic basis of metabolism and energy, the nature of irritability and motion, the electrochemical manifestations of cell vital activity, the essence of growth and aging, etc.).

Special physiology investigates the features of physiological functions in individual zoological subtypes, groups, classes of animals (insects, fish, birds, domestic or wild mammals, etc.).

Evolutionary physiology considers the emergence and development of the functions of the animal organism in the process of phylogenesis.

Ecological physiology studies the mechanisms of adaptation of animals to specific habitats.

Age physiology studies the dynamics of development and extinction of physiological functions in the process of ontogenesis.

With respect to pets, periods of growth, puberty and productive activity are of greatest interest.

The physiology of animals is closely related to other biological disciplines - anatomy, histology, embryology, biochemistry, biophysics, biotechnology, genetics, mathematics, it uses their methods and achievements. In turn, the physiology of animals, contributes to the development of the listed sciences.

Combining, integrating all gained biological knowledge, physiology provides a systematic approach to the study of the vital activity of the organism, treating it as a complex, integral and dynamic system actively interacting with the environment.

The purpose of animal physiology is to study and change the functions of animals in the right direction for increasing their productivity and fertility, improving the quality of their products and maintaining a good health status, and the veterinarian needs to know the normal course of physiological processes in the body

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of a healthy animal for understanding the nature of pathological phenomena, Development of means of prevention and treatment of patients.

Together with other sciences, physiology is the biological basis of rational animal husbandry. Modern zootechny and veterinary medicine widely use the achievements of physiology for practical purposes. So, on the basis of physiological data, the animal’s need for nutrients and energy is established and appropriate standards are developed; recommended scientifically based systems for growing young and keeping adult animals; effective methods of intensification of reproduction are introduced (artificial insemination of females, transplantation of zygotes, etc.); milking units and automation means for milking cows; training of sports horses and training of service dogs; the causes of a number of non-contagious animal diseases are investigated and measures for their prevention and therapy are developed; used biologically active substances - vitamins, antibiotics, hormones, tissue stimulants and other means that stimulate the growth and productivity of animals, etc.

1.2. Methods of physiological studies

The physiology of animals is an experimental science, its main method is experiment (experience).

Experiment (from the Latin experimentum - a test, an experiment), also experience, in the scientific method - a method of investigating some phenomenon under controlled conditions. It differs from observation by active interaction with the object under study.

The experiment serves as a source of knowledge about the processes of life, which are generalized in the form of hypotheses or theories.

1) Acute experience (vivisection) is a method of single use of animals during anesthesia, performed without observing the rules of aseptic and antiseptic. The goal is to get temporary access to in-

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ternal organs, and then to affect them (electrical irritation of nerves or muscles, vasoconstriction, application of targeted pharmacological drugs, isolation of organs, etc.), and the effect is recorded.

2)Chronic (long-term) experience is the method of using animals repeatedly after the performed operation with observance of the rules of aseptic and antiseptic. The aim is to study the physiological parameters of the body when applying fistulas to the stomach or intestine, removing the ducts of the digestive glands or ureters to get out secretions and excreta, implanting the electrodes to irritate the organ or diverting the biopotentials, removing individual organs or parts of them (for example, the thyroid gland, the brain), the imposition of catheters on the vessels of internal organs for the regular collection of blood samples, etc.

3)Simulation is a method based on the obtaining in the ex-

periment of some data expressed in the form of formulas, schemes that describe the patterns of the processes (animal growth curve, linear dynamic model of dairy productivity, etc.) and apparatus that mimic the work of any one, (electronic model of a nerve cell, model of an “artificial scar” in a ruminant, etc.).

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2.Physiology of excitable tissues

2.1.Main properties and conditions of excitable tissues

Cells and tissues of the body, specially adapted for the implementation of rapid responses to the action of the stimulus, are called excitable tissues. Excitable tissues include nervous, muscular and glandular tissue.

Excitable tissues have properties of irritability, excitability, conductivity and lability.

1) Irritability is the property of living tissues to respond to the action of the stimulus by changing metabolism and energy.

Irritation is the process of stimulus exposure to living tissues Irritability has both animals and plants, their lower and higher forms, it is inherent in all types of tissues. Irritability plays an important role in all manifestations of the vital activity of living organisms, in particular, it underlies the gradual adaptation of individual tissues and the organism as a whole to changes in the external and internal environment in the process of phyloand ontogenesis.

Irritant is an agent of the external environment or the internal environment of the body, which acts on the tissues, causing their excitation.

On the effect of stimuli (stimuli, stimulating factors), these cells react with a specific reversible change in ion permeability and membrane potential. These changes, in turn, are the most important components of the processes of excitation and inhibition.

The strength, duration and speed of reaction of excitable objects vary considerably. It depends on their structure, functional state, and also the nature of the stimulus.

Classification of stimuli:

By their energy origin, the stimuli are:

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-physical (mechanical, thermal, electrical, light, sound, radioactive radiation, etc.),

-chemical (acids, alkalis, salts, etc.),

-biological (venoms of snakes, insects, helminths, microor-

ganisms, etc.).

By biological significance for tissue irritants are divided into:

-adequate (specific) - these are stimuli capable of causing excitation of receptor devices and cells, which are specially adapted to perceive a given kind of stimulus under natural conditions of existence, with a minimum energy of stimulation. So, for retinal cells, the eyes are light rays (quanta of light);for auditory receptors, sound vibrations; for muscle fibers - a nerve impulse; for chemoreceptors that perceive the gas composition of the blood - carbon dioxide, etc.

-Inadequate (nonspecific) are such irritants, which normally

do not undergo tissue exposure in natural conditions, they also cause a reaction of excitable structures, but only with considerable strength and duration of action (for example, sensation from a flash of light when the eyeball is squeezed). In the experiment, the response of the excitable object (neuromuscular drug) can be caused by many nonspecific stimuli (pricking, squeezing, salt exposure, drying, heating, etc.). However, more often electric pulses of different shapes are used for this purpose.

Electric current is considered an adequate stimulus for excitable tissues, since their functional activity is always accompanied by bioelectric phenomena. Electric current is most often used as an irritant in experiments in the study of physiological processes in the body of animals. It can be precisely dosed by the strength, duration and nature of the effect on living tissue, while it does not injure the tissue and does not cause irreversible changes in it.

2) Excitability is the property of specialized (excitable) cells and tissues to respond to stimulation with a state of excitation.

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3)Conductivity is the property of excitable tissue to actively carry out a wave of excitation. So, the motor nerve of the cat conducts excitation at a speed of 120 m/s.

4)Lability is the speed with which a full period of a single exci-

tation pulse arises and ends in the tissue. The duration of this excitation, measured by the duration of the absolute refractivity phase, characterizes the rate of biochemical and physiological processes occurring in the tissue. The faster the processes that make up a separate impulse of excitation, the higher the lability. The longer the refractory period, the lower the functional lability.

The property of lability was discovered by N.E. Vvedensky (1892), studying the effect of rhythmic stimuli of different frequencies on the neuromuscular drug. To measure lability, an indicator is used - a measure of lability - this is the maximum number of excitation pulses that occur in 1 second in response to the same maximum number of stimuli. The myelinic somatic nerves have a high lability, while the smaller ones are the amyatotic autonomic nerves (500 and 200 pulses per second, respectively), the lability of skeletal muscles (200 pulses per second) is tens of times higher than that of smooth muscles. In the process of growth and development of the body lability increases, with aging - decreases.

The onset of excitation is accompanied by multiphase changes in excitability. Absolute refractoriness is the condition when the tissue temporarily does not react to repeated irritation during the onset and development of excitation. It lasts 0.5 ms and is replaced by a phase of relative refractoriness - a gradual restoration of tissue excitability, lasting 4-8 ms. For the emergence of the action potential in this period it is necessary to exert a greater force of irritation. Then comes the phase of exaltation - a temporary increase in the excitability of the tissue. Further, the excitability of the tissue is normalized.

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The main conditions of excitable tissues

According to modern ideas, excitable tissues in the process of their vital activity can be in three basic states: physiological rest, excitation and inhibition.

1)Physiological rest is a condition when the tissue does not show signs of its inherent activity. For example, the muscle does not contract. However, this state is conditional; in the living tissues, there are constantly complex processes of metabolism.

2)Excitation is an active state of living tissue, in which it

comes under the influence of stimulation, it is a complex biological reaction of an excitable cell to the action of the stimulus, manifested in a combination of physical, physico-chemical and functional changes.

The following signs of excitation are defined. Common signs for all excitable tissues include the change in the membrane potential, increased metabolism and energy, quantitative and qualitative changes in the physicochemical and chemical composition of the tissue. Specific signs of excitation are determined by the form of activity inherent only in this tissue: for nerve tissue - this is the generation of a propagating impulse, the synthesis and destruction of mediators; for muscle tissue - reduction; for glandular tissue - the formation and excretion of secretions.

Excitation can be local and spreading. Local excitation captures only individual structures of excitable entities. It occurs in areas of cell membranes that specialize in the perception of external stimuli (receptor membrane) or signals from other nerve cells (postsynaptic membrane). This excitation increases as the stimulation increases and, reaching a certain threshold value, passes into a spreading excitation that, according to the “all or nothing” principle, immediately acquires the maximum amplitude. Thus, local excitation can be considered as an initial stage, a trigger mechanism of spreading excitation. However, in excitable tissues of relatively low organization (in particular, glandular epithelium), local excita-

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