General physiology of excitable tissues. Physiology of muscles and nerves. Features of functioning of muscles of maxillar-facial area.

 

Human and animals’s organism has the highest ability to adapt to the constantly varying conditions of external and internal medium. In the basis of adaptive organism reactions lies the universal property of alive tissue - irritability - the ability to respond to the irritating factors action by metabolism change. The irritability is evolutionally the ancient form of tissues reaction. During evolution gradual differentiation of tissues participating in adaptive organism activity has taken place. The irritability in these tissues has reached the best expression and has received the name an excitability. The excitability is an ability of a tissue to respond to an irritation specializedly, singlemindedly and with the maximal velocity. Excitement – complex (difficult) biological process expressing by response reaction to an irritation.

A nervous, muscular, epithelial, secretory tissue (excitable tissues) have an excitability. The specialized form of response reaction is an excitation process physiological display. A contraction will be a response reaction in any muscular tissue. At a nervous tissue it will be an impulse conduction. At a secretory tissue it will be a synthesis and allocation of biologically active substance.

The excitability of tissues is various. A measure of an excitability is the threshold of stimulation – minimal stimulus force, capable to cause excitation.The stimuli with a size that is less than a threshold one, are called subliminal ones.The stimuli, on force exceeding a threshold of stimulation are called epiliminal ones.

All stimuli can be divided into three groups: physical, chemical and physico-chemical. Physical stimuli - mechanical, temperature, light, sound and electrical ones. Chemical stimuli - acid, alkalis, medicines. Physico-chemical stimuli –osmotic pressure, рН, ion structure changing. Besides, they distinguish biological stimuli - hormones, vitamins and others, biologically active substances. They allocate also a group of social stimuli - a word.

All stimuli divide on adequate and inadequate on biological value. Adequate stimuli are such stimuli, acting to the given biological structure under natural conditions and to perception of which it is adjusted specially (e.g., for eye retina photoceptors the seen part of light is an adequate stimulus). Inadequate stimuli are such, to perception of which the given structure is not adjusted specially (e.g., for a sceletal muscle the adequate stimulus is the nervous impulse, but it can contracts at a mechanical impact too).

Characteristic attribute of exaltation is an electrical current occurrence in tissues (cells). The electrical phenomena (currents or potentials), which arise in organism cells, tissues and organs are named the biological potentials.

Biological potentials arise because there is a difference of potentials between the external and internal parts of a cell membrane, which is in a rest status. Potential, which is registered in a such cell status, is named a membrane potential (resting potential). It is caused by the difference of a potassium, calcium, sodium, chlorine and other ions concentration between intracellular and extracellular medium. So, the potassium ions concentration in a cell exceeds in many times (about 20-40 times) their contents in extracellular medium. Sodium ions concentration, on the contrary, is lower in intracellular medium in 10-20 times. The ions of chlorine, as well as of a sodium, are mainly concentrated outside of cell membrane, where their content is in 15-20 times more than inside. Their such non-uniform distribution till that and other membrane parts provide ion pumps. Ion canals, available in a membrane, can be opened and closed, that depends on a membrane status. So, in a cell which is in a resting status, the sodic canals are closed, and the potassium ones - are opened. Therefore the permeability for different ions is various. If a potassium ions permeability to accept for 1,0, for chlorine it will make - 0,45, and sodium - 0,04. It results that the potassium ions on a concentration gradient diffuse from a cell to extracellular space. The sodium ions counter flow is a very small. In a result the potentials difference between cell internal medium and its outer surface is formed which is from 50 up to 100 mV for different tissues. This potentials difference also refers to as a resting potential or a membrane potential.

At stimulus action there is a membrane status change, ion canals open in it, through which positively charged ions available in excess behind its limits can move in a cell. The "fast" sodic canals opening occured most often. Originally ion current to cell is promoted also by a transmembrane potentials difference. Such process is called depolarization, because it results in this potentials difference reducing. If the stimulus is weaker (subliminal), ion canals are opened a little, therefore the ion current is insignificant. Depolarization occurs slowly. Such changes are named the local depolarization or local potential.

If threshold stimulus acts, the depolarization reaches a critical (threshold) level. As a result of it all active electroexcitable ion canals are opened. Depolarization is sharply accelerated and there is even a potential reversion (potential mark change). Thus the positively charged sodium ions flow stops, the appropriate canals are closed. Excessive potassium ions from inside direct outside, resulting to the membrane potential restoration. At first it occurs rather quickly (fast repolarization), and then, when the potassium ions flow decreases, the membrane potential restoration occurs in a slowed-up way (slow repolarization). Further potassium ions exit can proceed and cause a hyperpolarization. Potassium-sodic pump work adducting in initial potentials difference restoration (to polarization) amplifies at this time. All this process from a beginning up to the end is called as an action potential.

As the vital activity of all cells, tissues, organs is accompanied by their electrical activity, the registration of potentials, arising at it, allows to judge processes occurring in them. The diagnostics and control of a treatment of this or that disease is based on it. For example, in a heart such registration of its biological potentials wears the name electrocardiogram (ECG).

In physiology they determine one more property of excitable tissues, which has received the name a lability. It is a functional mobility of tissues, its parameter is the potentials action maximal number, which the excitable tissue is capable to generate per 1 second according to a rhythm of a submitted boring (irritation). The normal size of a lability, e.g., for a nervous tissue makes 500-1000 impulses per second, and for sceletal muscles - 150-200 impulses per second. There is a sceletal muscles lability rising with ageing. It is shown in augmentation of irritation freaquency, at which the gear (incomplete) tetanus turns in smooth. In newborn’s muscles it occurs at a stimulus freaquency 4-20 per second, at adulthood - 50-100 impulses per second.

The general laws of tissues functionning. Between the irritation character and the answer-back reaction of an alive tissue there are close mutual relations, which find expression in the irritation laws.

Irritation force law: the more force of an irritation, the more strong answer-back reaction (up to known limits). The further stimulus force augmentation any more does not lead to the answer-back reaction increasing, and even can cause return reaction, down to its disappearance. It is explained by that each functional unit of tissues (for example, muscular) has its exaltation threshold. That’s why while working the threshold stimulus, those fibers, for which this stimulus is of a such size are only involved in the answer. Others do not react.

At stimulus force augmentation the new fibers are involved, for which the given stimulus is a threshold etc. Further, when the stimulus force will exceed the opportunities of all fibers of the given tissue, its answer-back reaction to the force augmentation will not change (the resources are settled!). Such irritators, which cause the maximal answer-back reaction, are named in physiology maximal or optimum. At the even greater stimulus force augmentation the answer-back reaction even will decrease, as at such a stimulus force the separate functional fibers of excitable tissues can even be injured. In a result, the answer-back reaction decreases and this phenomenon in physiology is named pessimum, and the stimuli causing it - pessimal.

The law "everything" or "nothing" is shown, first of all, at the cardiac muscle work analysis. According to this law, subliminal stimuli, acting to a cardiac muscle, do not cause an answer in it (it is "nothing"), and threshold and epiliminal stimuli cause answer-back reaction of the same size (it is named "everything"). Under the same law the functional unit of any excitable tissue works. Let's take, for example, a muscular fiber and we shall imagine, that threshold stimulus at it is 2В (electrical current strain or voltage). If we act the stimulus of 1V to it, we naturally shall not receive any reaction ("nothing"), and if we take the stimulus of 4V, the muscle will give the same answer-back reaction, as well as on 2V ("everything"). Naturally, "everything" and "nothing" are relative concepts, as at the subliminal stimulus action there is a local answer (local potential), therefore it already cannot be treated as "anything".

The law of force-time – with the augmentation of a stimulus force it is required less time of its influence to tissue for answer-back reaction reception. The relation between the duration and force can be expressed by hyperbolic curve, the both branches of which go at any stage in parallel to axes of coordinates. This last circumstance forms the basis that the stimuli of a very small size (less than the threshold) can not cause the answer-back reaction.

 

Physiology of muscles. As it is known, muscle is the contractile unit of body. Nearly 40% of the body is skeletal muscles. There are 2 muscles types:

1. Striated muscles:

· Skeletal muscle

· Cardiac muscle

2. Unstriated muscles - smooth muscles of inner organs, skin and vessels.

One can differentiate 3 muscles types: skeletal, cardiac and smooth.

Skeletal muscles physiological properties. Skeletal muscles possess excitability, conduction, contractility, lability (ability to reproduce the irritation freaquency). At a muscle irritation by single stimulus the single muscular contraction arises. One can distinguish the latent period (from irritation beginning to answer-back reaction beginning), shortnening period (actually contraction) and relaxation period. In reply to a rhythmic irritation (namely the such one our muscles are received) the muscle is reduced lengthly (for a long time). Such contraction has received the name tetanic or summarized. If each subsequent pulse approaches to a muscle in the period, when it began to be relaxed, there is an infused or incomplete tetanus. If the interval between irritations decreases so, that each subsequent pulse comes to a muscle, at that moment, when it is in a contraction phase, there is a smooth tetanus.

In a certain degree the tetanus formation mechanism is explained by superposition phenomenon. However, it can be caused by excitability changing as well. And if to take into account, that the excitability changes are caused by membrane potential change features during exaltation, then it is easy to explain smooth tetanus occurrence and its size. Let's try to understand this phenomenon together. If to render an irritation to muscle during its contraction (smooth tetanus) or relaxation (incomplete or infused tetanus), it is necessary on that moment the excitability increasing existance. Why it’s so? At this time the slow depolarization phase develops in a muscle, when the membrane potential is lower, than in rest state, but is higher, than threshold potential. That’s why even subthreshold (subliminal) stimulus will cause the depolarization acceleration (i.e. the excitability at this time in a muscle is raised - supernormal excitability). Fast depolarization beginning results in the situation when the tissue loses ability to react to an irritation. This phase refers to as absolute refracterity (absolute inexcitability). At repolarization time the excitability is restored. This period refers to as relative refracterity. An excitability at this moment is below than the initial one, and only strong (epiliminal) stimuli can cause the answer-back reaction. Then when the restful (remainded) repolarization develops, the excitability grows and becomes above initial. This phase refers to as exaltation (hyperexcitability). During its occurrence even subliminal stimuli can cause the answer-back reaction. Precisely at this moment the threshold stimuli also cause the phenomenon of a tetanus (both infused, and smooth). That’s why this reaction is more on size, than the single muscular contractrion. Further a membrane hyperpolarization comes and the excitability falls, it is a a subnormal excitability phase. At this moment the epiliminal stimulus is required to cause the answer-back reaction.

Under natural (physiological) activity conditions in human being organism the muscle shortness degree can be various.

One can differentiate the following types of muscular contraction according to the shortness size:

1) isotonic is the muscular contraction, at which its fibers are shortened at a constant external load (under real conditions such type is practically absent);

2) isometric is a muscular activation type, at which it develops a strain (tension) without the length change, it underlies the static work;

3) auxotonic is a regimen, in which the muscles develop a tension and are shortened, such reducings are the characteristic of walking, run, sailing.

 

Muscles have certain force. Myodynamia (muscle force) is the greatest load size, which it can lift. There is a concept of an absolute muscle force -it is a maximal load, which the muscle lifts on 1 sm of transversal physiological section. For example, at a masseter it makes - 10,0 kg /sm². Besides there is a concept of a relative muscle force. It is the muscle ability to rise of a load on unit of a muscle anatomic section (is measured in kg / sm²).

Muscular force grows during all period of a childhood, but especially intensively - in young age. At the second childhood period beginning the force of the majority of muscular groups in boys and girls does not differ. By 12-15 years of age, the muscles force in boys becomes approximately on 30 % more, than in girls. With age especially after 8 years, the ability to performance of long muscular work – endurance - is enlarged. It is higher in boys.

Muscular work is determined by product of mass of the lifted load on muscle shortage size. All human muscles useful action coefficient is equal to 15-25 %, at trained people it is higher - 35 %. There is a law of average loads, at which the muscle is working for a long time at average loads in an optimum (average) contraction rhythm. At long-termed exercise the working muscular hypertrophy develops. There occurs the whole musculation mass and each muscular fiber mass augmentation. At a hypodynamia muscles atrophy comes. At long mode of operations of muscles weariness comes - subjective status, and then the fatigue develops. Objective attributes of ability to work hard decreasing join to the feeling of weariness: force, endurance, rate of impellent (motor) reactions falls. One can distinguish the acute fatigue - the result of a hard work (for example, sport competitions) and the chronic fatigue - the result of repeated regular influence of loads without regular rest.

Fatigue reasons:

1) metabolites accumulation (lactic, pyruvic and other acids, ions suppressing an action potential) in muscular tissue;

2) power (energy) musclular stocks exhaustion (glycogen, ATP);

3) infringement as a result of a muscular circulation tension;

4) nervous centers efficiency (capacity for work) change. The efficiency is quickly restored at active rest, when there is activity kind change or change of working bodies (organs).

In musclular work there can be two statuses:

1) dynamic - there is a load moving and movement of bones and joints;

2) static - the muscular fibers develop a strain (tension), but are not shortened almost (deduction or restraining of a load). The static work is more tiring, than the dynamic one.

In a whole, the sceletal muscles play an important role not only in body moving in space, parts of a body opposite each other, pose maintenance, but also they take part in blood and lymph movement, heat producing, an inspiration and exhalation (expiration) act, they are the depot of liquids and salts, glycogen, provide mechanical protection of cavitary bodies (organs). And, at last, the movements caused by skeletal musculation work, are the powerful antistressful factor.

Facial-maxillar region muscles functionally are divided into masticatory and mimic. They belong to sceletal muscles group and possess the same physiological features like other sceletal muscles. For example, in course of masticatory muscles fatigue development their retarded relaxation can occurs that is named as masticatory muscles contractura. Mouth opening and thus feeding act and food mechanic processing destroyes at this. Masticatory musculature belongs to force muscles. Muscle with transversal surface in 1 cm² can develop force in 10 kg while its contraction. Masticatory muscles transversal surface sum for muscles rising mandibule on one face half is equal to 19,5 cm², on both sides – 39 cm². Thus, masticatory muscles absolute force is 390 kg. Alongside with big masticatory muscles absolute force there is separate teeth parodont low resiliency. That’s why at jaws enforced occlusion painful sensation occurs. For base dental tissues resiliency determining as for pressure one can use gnathodynamometry method which is performed by means of special devices (gnathodynamometers). It was established that frontal teeth parodont resiliency is approximately equal to 60 kg, masticatory ones – 180 kg.

Muscular contraction is accompanied by bioelectrical phenomena: action streams occur in muscles, potentials of which one can registrate by means of electronic enforcements as electromyogram (EMG). On masticatory muscles EMG one can see muscles-antagonists, providing mandibule movement, alternating activity. Masticatory muscles bioelectrical activity varies significantly dependently from occlusion type, dental rows, dental nervous tissues and parodont state, dentures construction and many others factors.

EMG analysis in investigated people with intact dental rows testifies that under norma one can see symmetrical muscular activity and distinct phase change (of bioelectrical muscular activity and resting period). Biopotential oscillations are spindle-shaped. At relaxation of muscles elevating mandibule potentials are absent. At masticatory teeth loss from one side masticatory muscles activity on this side is sharply decreased. At a significant teeth loss masticatory muscles potentials decreasing occurs.

EMG is also a method that encourages to discovery of different muscles (mimic too) denervation and paresis. EMG indicates to pathological process localization level.

Besides, muscular and nervous excitability determining for maxillo-facial region is widely used in dentistry. It can be performed by means of chronaxymetry method. By means of muscle chronaxy measurement (minimal time in course of which a stream that is equal to double threshold – rheobase – acts to the tissue and causes excitement) doctor can determine motor nerve fibres injury existance. It is possible because while electrical stimulus application to the muscle electrical current comes through the nerve innervating it too. That’s why at muscular irritation excitation appears primarily in nervous fibres and than transmits to the muscle. The result – in fact, at normal muscle chronaxy determining one determine chronaxy of nervous fibres innervating it. If the nerve is injured or spine motoneurons innervating muscle are dead, nervous fibres are degenerated and than electrical stimulus applied to muscle expresses muscular fibres chronaxy that has bigger duration.

Chronaxy and rheobase indexes are inversely proportional to the tissue excitability level. They can vary significantly at trigeminal and facial nerves neuritis and neuralgias as well as at mimic and masticatory musculature myosites.

For dental pulp excitability determining one can use temperature (warmth, coldness) and mechanical (percussion) stimuli as well as electrical current. Electrical current has some advantages in comparison to other stimuli. It permits to act on pulp through enamel and dentine, can be dosated easily and exactly, doesn’t hurt tooth pulp, that’s why it can be applied many times.

Tooth electroexcitability investigation is in fact an investigation of excitability of corresponding sensory nerves and tooth pulp.

Electrical current application for teeth excitability determining with diagnostical aim is called electroodontodiagnostics. Tooth reaction to electrical irritation permits to determine specific picture of tooth electroexcitability changes in course of different pathologic processes. It was established that healthy teeth independently from group belonging have equal excitability answering to the same current force from 2 to 6 mcA. If tooth irritation threshold is less than 2 mcA, it testifies to excitability increasing (it is observed for example at parodontosis). At pulpites on the contrary one can determine irritation threshold increasing more than 6 mcA. Excitability decreasing up to 100-200 mcA is a pulp death sign. In such a case periodont tactile receptors react on.

Oral mucosa is a highly-sensitive to electrical current because it has good electroconductance. From Galvani experiment one can make the conclusion that different metals are the origin of so-called galvanic current which can irritate alive tissues. This fact dentist must take into account while teeth denturing and plombing with different metals (gold, inrustining steel et al.) that act as electrodes. In this case saliva is a good electrolyte. Occuring microstreams can be a reason of phenomena called galvanism in dentistry.

In dentistry electrical current is used also for treatment. Constant uninterrupted low-tension (30-80 V) and low-forced electrical current (up to 50 mA) for treaty aims is called galvanization. In course of such current action vasodilatation occurs in oral mucosa. Blood circulation acceleration, vessel wall permeability increasing are accompanied by temperature increasing and hyperaemia. Vessel reactions permit local metabolism activation, epithelium and connective tissue regeneration.

Electrical current helps to introduce drugs in tissues (medical electrophoresis), cause anaelgesia (electroanaelgesia).

Nervous fibres and nerves physiology.

Nervous fibres possess excitability and according to morphologic principle they are divided into myeline and myeline-free. Nervous fibres form nerve or nervous stem, consisting of great amount of them. Nervous fibres transmitting excitation from receptors to central nervous system (CNS) are called afferent; from CNS to the effector organs – efferent. Nervous fibres possess: excitability, conductance, lability. Nervous tissue excitability is higher than muscular one. It is various in different nervous fibres. Myeline (thick) nervous fibres is significantly higher than myeline-free (thin).

Excitement conductance through nervous fibres obeyes definite laws.

Physiological integrity law

tells that excitation conductance through nervous fibre is possible only in a case of its non-interrupted anatomical structure and physiological features.

Excitement conductance two-sided law

at irritation application on nervous fibre the excitement is diverged through it in both sides from irritation place (at tooth nerve irritation pain is stretched not only on local tissues but also irradiates in other body parts).

Excitement isolated conductance law

excitation through nervous fibres being in a composition of mixed nerves (for example, vagus) is diverged separately, i.e. it doesn’t transmit through one nervous fibre to another.

Excitement conductance velocity is different in nervous fibres. It depends on their diameter and structure (myeline membrane existance). All nervous fibres are divided into 3 main types according to their conductance velocity. Type “A”fibres – are covered by myeline membrane (sceletal muscles motor fibres), excitement wave conductance velocity is up to 120 m/sec. Type “B”fibres – vegetative nerves myeline fibres, excitement wave conductance velocity is up to 18 m/sec. Type “C”fibres – myeline-free nervous fibres (vegetative or autonomic nervous system postganglionar fibres), excitement wave conductance velocity is up to 3 m/sec.

Excitement conductance mechanism through nervous fibres. Excitement spreading through nervous fibres is based on bioelectrical potentials ion generation mechanisms. At excitement spreading through type “C” fibre local electrical currents occuring between excited locus, charged electronegatively, and unexcited, charged electropositively, cause simultaneouse membrane depolarization till its critical level with further action potential generation in every membrane point through all the stretching of nervous fibre. Such excitement conductance is called uninterrupted.

Myeline membrane presence, possessing high resistance, and membrane locuses, not having it, creates conditions for “saltatory” excitement conductance through myeline nervous fibres of types “A” and “B”. Local electrical currents occur between neighboring Ranvier’s nodes because excited membrane of node becomes electronegative as for the surface of neighbouring unexcited node. Local currents depolarize membrane of unexcited node till critic level and action potential occurence. Thus, excitation “jumps over” nervous fibre locuses covered by myeline, from one node to another. Such excitement conductance velocity reaches 120 m/sec. At the same time, such excitement wave conductance is more economic than the uninterrupted one.

Nervous fibres possess lability – the ability to reproduce definite number of excitation cycles in time unit according to the rhythm of applied irritations. Lability measure is maximal excitation frequency which nervous fibre can reproduce in time unit according to the rhythm of received irritations. Nervous fibre lability is the highest and is approximately 1000 impulses per second.

Important characteristics of nervous fibre is its relative indefatigueability, which depends in many aspects on the fact that energy losses in it are insignificant in course of excitement and repair processes pass quickly. Besides, nervous fibre pass excitement wave with large underloading (it can transmit up to 100 impulses/sec but in the most cases transmits less for normal physiological reactions).

In dentistry for analgaesia in the most often cases one use local anaesthesia one type of which is conductive analgaesia. It is based on nervous fibre physiological integrity law. Drug introduction disturbs nerve physiologic integrity that prevents excitation spreading in pharmacological blockade zone. In your future practice you will widely use these physiological data while dentistry practical tasks decision.

 

 

Lecture 2

Central nervous system and endocrine glands role in oral cavity physiological functions regulation

Human organism is a complicated, highly-organized system consisting of tissues, organs and system connecting one to another. CNS provides with endocrine apparatus their functions of co-ordination, organism connection with environment and individual human organism adaptation according to their internal necessities. Human activity as complicated reactions realizing with CNS participation is called reflectory, with the endocrine apparatus participation – humoral. CNS activity main mechanism is reflex – conditioned organism reaction by external or internal environment action.

Physiologic functions central regulation. CNS is a complicated structure consisting of

large amount of interacting nervous centers. Anatomically nervous center is an integrity of neurons located in a definite brain part and are essential for definite reflex performing. Physiologically nervous center – is a complicated functional unity of many nervous centers located in different CNS parts and providing difficult reflectory acts and organism functions regulation due to their integrative activity. Examples – respiratory center, heart-vascular center et al.

Nervous centers features. Nervous centers possess a row of character features and peculiarities of excitation conductance, which are determined significantly by synaptic formations presence and structure of neuronal chains forming these centers. These synapses transmitting excitation received the name exciting. Some functional features are characteristics of them. They are also nervous centers features.

One-sided excitement conductance in nervous center is determined by its one-sided conductance through synapses.

Excitement conductance lack – is connected with the fact that excitation wave is transmittered slower in synapse than through nervous fibre (it’s necessary time for mediator accumulation and exciting post-synaptic potential EPSP forming). EPSP – size on which membrane potential of post-synaptic membrane in decreased while acting mediator portion on it.

Excitement summation – can be temporary or simultanenous (it is delt with EPSP accumulation in one synapse) and space (linked with EPSP accumulation in different synapses of one and the same neuron).

Excitement rhythm transformation – impulses number increasing or decreasing on neuron “exit” in comparison to impulses number which it receives on “entrance”.

Afteraction. Reflectory acts are ended not at the same time with stimulus action stoppage but they are lasted for long after action stoppage.

High sensitivity to hypoxy and different chemical substances. It gives opportunity to well-directed brain functions pharmacological regulation.

High fatigue is a result of nervous centers low lability and mediator consumption for EPSP formation.

There are also special inhibitory synapses in CNS the role of which are to inhibit excitation wave conductance. The same processes in comparison to exciting synapses take place in inhibitory ones. The difference is that inhibitory mediators cause in such synapses membrane inhibitory post-synaptic potential (IPSP) occurence. IPSP – is that size on which post-synaptic membrane potential is increased while action inhibitory mediator on it.

Inhibition in CNS is of great importance. First, it performs co-ordinative role, i.e. directs excitation on a definite way to the definite nervous centers. As a result of such action well-directed elective excitation irradiation occurs. Excitation in nervous centers due to irradiation can converge from different origins to one and the same neuron. Due to interrelations between excitation and inhibition processes in CNS dominanta principle is expressed in its work. It is main working principle for nervous centers activity which is expressed in temporary dominant excitation locuses occurence.

Besides very important role in reflectory activity co-ordination, inhibition performs important protective role or defencive function. Multiple organism reactions are formed with obligatory participation of different CNS parts on the basis of excitement and inhibition processes interaction.

In course of some dental diseases durable painful syndrom can create locuses of dominant excitation in corresponding nervous centers. Under such conditions any side stimuli (touching, bright light, strong noise) enforce the pain.

Besides, oral cavity different functions disorders can be determined by central brain structures injury. First of all, posterior brain structures (pons and medulla oblongata), where the centers of trigeminal, facial, glossopharyngeal, sublingual and vagus nerves are located, belong to them. Modern investigation methods (electroencephalography, EEG) are used in clinics for determining the role of different brain structures in pain mechanisms forming in dental patients, for oral cavity functions localization in brain, for separate neurons functions peculiarities study in a zone of cortical oral cavity organs representation. It was established on the basis of these investigations that painful excitations occuring at dental pulp irritation irradiate widely in subcortical structures and brain hemispheres that leads to intensive painful sensations occurence.

Oral cavity organs functions are regulated by vegetative nerves. Autonomic (vegetative) nervous system – is a complex of central and perypheral structures which regulate internal environment functional level necessary for organism adequate reaction. Anatomically autonomic nervous system is represented by nuclear structures lying in brain and spine, nervous ganglions and nervous fibres. It is divided morphologically and functionally into 3 parts:

· parasympathetic;

· sympathetic;

· metasympathetic.

Autonomic nervous system reflexes morpho-functional peculiarities. Parasympathetic part. Parasympathetic unit central part is represented by nuclei, located: in midbrain- oculomotor nerve nucleus (III-rd pair of craniocerebral nerves); in medulla oblongata – facial (VII-th pair), glosso-pharyngeal (IX-th) and vagus (X-th pair) nerves nuclei; in spine – lateral corns of sacral part 3 segments. Perypheral part includes: preganglionar fibres – nervous fibres coming from nervous centers, ganglions and postganglionar nervous fibres – innervating effector organs.

Parasympathetic vegetative functions regulation is realized by both highest nervous centers (cerebral and spinal) and by perypheral ones – ganglions. Ganglion is a morphologic and functional unity of neurons. Excitement transduction from preganglionar nervous fibre to postganglionar is realized in parasympathetic ganglions by means of mediator – acetylcholine. When excitation reaches preganglionar fibre therminal, permeability increasing for extraneuronal calcium occurs. Calcium comes in presynaptic membrane zone and activates vesicules transport with acethylcholine to presynaptic membrane. Vesicular membrane is fused with presynaptic membrane. It creates the conditions for mediator releasing into synaptic fissure. Acethylcholine interacts with N-cholinoreceptor on post-synaptic membrane and sodium channels are opened as the result of which EPSP occurs. Acethylcholine is destroyed by enzyme acethylcholineestherase after this interaction. Substances which act like acethylcholine are called agonistes, inhibiting excitement conductance in ganglions – ganglioblockers.

In postganglionar parasympathetic nervous fibres on their endings realization is performed through synapses by means of acethylcholine which in visceral organs (heart, alimentary organs, bronchi et al.) acts through M-cholinoreceptors (muscarine-dependent). Such receptors are not equal. One can differentiate M₁…M₅ receptors. Besides, one can differentiate also N-cholinoreceptors (nicotine-sensitive), located on post-synaptic mebranes of sceletal muscles, in central nervous system. Physiologic effects depend on which receptors acts acethylcholine.

Parasympathetic influences peculiarity on different organs is the following: effect comes quickly because they mainly consist of preganglionar nervous fibres of group “B” where excitement wave spreading velocity is relatively high. But effect also disappears quickly because mediator acethylcholine is destroyed fast. That’s why action of this part of autonomic nervous system is quick and in more extent local (in the place of mediator releasing).

Sympathetic part. Central part is origined from spine nuclei in grey substance beginning fromI-II thoracic till II-IV lumbal segments. Perypheral part is represented by postganglionar neurons beginning from paravertebral and prevertebral ganglions. Excitement conductance in ganglions in this part of autonomic nervous system is realized by mechanisms similar to those in parasympathetic nervous system. Excitation wave is transmitted from postganglionar fiber to effector by means of mediator – noradrenaline (or adrenaline). Noradrenaline produces in body, axonal therminal part and its varicosus dilations. Noradrenaline is located in neuronal vesicles, its part is dissolved in cytoplasm. It is released from vesicules in course of depolarization of presynaptic ending membranes that is accompanied by their permeability changes to calcium ions. Calcium releasing into synaptic fissure occurs by means of exocytosis – vesicular membrane fusing with axonal ending membrane. Noradrenaline or adrenaline reaching postsynaptic membrane interacts with specific receptors which name is adrenoreceptors. They are divided into 2 groups – alpha- and beta-adrenoreceptors. In turn, every group is subdivided into subgroups. Alpha-adrenoreceptors activation leads to skin, mucosas, kidney, abdominal cavity organs, lung, brain, sceletal muscles vessels constriction. At the same time it results in contraction of sphincters smooth muscles and pupil ciliary muscle, causing midriasis (pupil’s dilation).

Beta-adrenoreceptors activation causes vasodilatation in sceletal muscles, coronars, lung, brain, abdominal cavity organs. It also leads to heart beat, freaquency and excitement conductance velocity increasing in typical (working) and atypical myocardiocytes. Other results of such activation – pupillar muscles, biliary tracts smooth muscles relaxation; urinary vesicle tone decreasing.

Autonomic nervous system sympathetic part makes trophyc influence onto different tissues and organs. It means that metabolic processes complex occurs in tissues supporting tissue structure and providing its function and metabolic reactions in it. For example, it enforces energy substances resynthesis processes, changes receptors excitability et al. Biologically active substances – noradrenaline and adrenaline – participate in trophyc processes. They while absorbing into blood are spread to organs and tissues which have no sympathetic innervation and act to them (for example, sceletal muscles).

Comparatively to parasympathetic part, sympathetic one influences more diffusily. It is connected with adrenaline and noradrenaline action because they reach practically all tissues and organs and possess stronger effect in comparison with acethylcholine. Besides, sympathetic nervous system action and influence is more durable.

Metasympathetic part is a complex of structures providing their own nervous regulation of main visceral organs possessing functional automatism (cardiometasympathetic, enterometasympathetic, urethrometasympathetic). Its main functions are as follows as: providing excitement conductance from nervous system structures to effectors, regulatory influences co-ordination performing (of smooth muscles motor activity, alimentary tract organs secretory, excretory and absorbtive activity, local circulation regulation and others).

The base of metasympathetic part are neurons different in their shape, synapses existance, processes amount and length. This system ganglions are located intramurally – in organs walls. Parasympathetic and sympathetic fibres penetrate these ganglions. Central influencings are realized through these fibres. Ganglionar neurons receive and process the information from efectors and are under modulating and correcting influence of impulses coming from brain and spine centers. Information processing is performed in ganglions, excitement transmitting in them is realized with acethylcholine participation (through M- and N-cholinoreceptors) and noradrenaline (through alfa-adrenoreceptors). Impulses are transmitted from postganglionar neurons to effectors by means of such mediators as ATP, serotonine, noradrenaline, acethylcholine, substance “P” and others. Significant role in effects realizing to effector tissues and organs have modulators – kinines, prostaglandines, opioid peptides, renine, angiotensine and others. They change effectors functional answer enforcing or decreasing their activity.

Thus, autonomic nervous system action onto organs and tissues is not equal. Sympathetic part causes their diffuse excitement. This is the system of anxiety, protection, mobilization of reserves necessary for organism interaction with environment. Such mobilization is reached by means of many systems and organs generalized involvement in reaction. Probably, that’s why sympathetic ganglions are situated far from innervated organs and possess the ability to impulses multiplication that provides fast influencing generalization.

Slower but also generalized process appears at adrenaline releasing into blood. Such releasing is considered to be fluid sympathetic nervous system. Sympathetic impulses activate brain activity, mobilize defence reactions, thermoregulative processes, blood coagulation mechanisms, immune reactions. Sympathetic nervous system excitement is an obligatory condition of emotional state and tension, it is hormonal reactions initial stage (link) at stress. Its influencings have adaptative and trophyc character.

Parasympathetic part and, especially, metasympathetic are the systems of current organism physiologic functions regulation. Such functions provide homeostasis. Metasympathetic neurones possess the features like brain nuclear structures. This system has its own integrative chain for information processing. If parasympathetic system influencings are mainly indirected (although there are also direct influencings to some organs) and more local than in sympathetic, metasympathetic one has only visceral functions (peristalsis saving, absorption, smooth muscles contraction) and it is base, local for these organs.

Vegetative functions regulative centers are practically all parts of central nervous system. Spinal part has segmentary and metameric organization. It’s a very important for clinics (hyperaesthesia, hyperalgesia – tactile and nociceptive sensitivity increasing in limited body parts at inner organs diseases). Pains occuring at inner organs diseases are called reflected (Ged’s zones).

In brain stem there are multiple vegetative structures – nuclei and centers of heart activity, vessel tone, respiration, swallowing regulation and others. They must belong such reflexes as olfactory, lacrimal, pupillar, sneeze and others to these reflectory acts.

In dieencephalon particularly in hypothalamus humans have central mechanism of homeostasis, alimentary, respiratory functions, heart-vascular activity, endocrine system, metabolism regulation, thermoregulation.

Somatosensor and other cortical zones are center of localization not only of somatic but also visceral systems.

Autonomic nervous system reflectory reactions. One can differentiate 3 reflexes groups:

· viscero-visceral;

· viscero-somatic;

· viscero-sensor.

Viscero-visceral reflexes are origined and are ended in inner organs. For example, peritoneum receptors in course of their excitement give impulses changing heart activity (Golz reflex, epigastral reflex). Such reflexes may be closed by type of axon-reflex (in limits of one axon branches). It’s necessary to take into account such mechanism of their occurence in clinic practice in course of therapeutical procedures performing (mustard plusters, cupping-glasses, compresses).

Viscero-somatic – include ways on which excitement cause also somatic answers (contraction or inhibition of sceletal muscles current activity) in addition to visceral reflexes. Segmentary innervation of some organs (heart, intestines) are on the base of these reflexes. It’s accompanied by integrative reactions of both visceral and somatic organs. For example, abdominal cavity receptors irritation can cause anterior abdominal wall muscles contraction or extremities movement that it is connected with afferent impulses convergence to interneurons of different spine segments. Such segments create common scheme for autonomic and somatic influencings transmission.

Viscero-sensor – include ways in which in answer to autonomic sensor fibres irritation reactions occur not only in inner organs, muscular system but also somatic sensitivity is changed. Due to segmentary organization, autonomic and somatic innervation at inner organs diseases in limited skin locuses tactile and nociceptive sensitivity increasing (reflected pains) is appeared. In course of some diseases (stenocardia, ulcer disease, cholecystitis, pancreatitis et al.) the patients’ complaint is painful sensation in corresponding proectional zones.

Vegetative innervation disorders are often observed in dentistry. They have very different signs. For example, salivary glands secretion changes (glands have double innervation – sympathetic and parasympathetic), at swallowing, food gustatory qualities assessment. One can see oral cavity tactile, temperature sensitivity disorders and many others.

Oral cavity physiological functions nervous regulation is the highest stage of development and organism adaptation to environment changing conditions. Nervous regulation is more perfect and more complicated by its mechanisms. But there exists also more ancient form of interaction between cells of multi-cellular organisms – chemical influence of metabolism products secreted by special cells and organs (endocrine glands) – hormones. It’s difficult to separate these 2 functions today because brain one can consider endocrine gland. Functions regulation is realized through blood. Thus, humoral regulation is more ancient. Under natural physiological conditions they work with co-operation.