General physiology of General physiology of excitative tissue. excitative tissue.

Physiology of muscles Physiology of muscles and nerves. Features of and nerves. Features of functioning of muscles functioning of muscles

cranial facial area.cranial facial area.

DETERMINATION OF “PHYSIOLOGY” DETERMINATION OF “PHYSIOLOGY” NOTION.NOTION. PHYSIOLOGICAL SUBJECTSPHYSIOLOGICAL SUBJECTS

Physiology is the science about the regularities of organisms‘ vital activity in connection with the external environment  

PHYSIOLOGICAL SUBJECTS  1. Aged physiology2. Clinical physiology.3. Physiology of labor.4. Psychophysiology.5. Ecological physiology.6. Physiology of sport.7. Space physiology.8. Pathologic physiology.

Methods of physiologyMethods of physiology• a) Observation (This is the method in which the scientists

don‘t mix in course of vital processes. They only make use of vision and description of all changes. On the base of this changes they make conclusions.)

• b) Experiment (There are two kinds of experiments: acute and chronic. Acute experiment was doing with the helps of anesthesia. It may be accompanied by cut off the nerves, introduction the different substances. The chronic experiment was doing in vital animals, for example, after the acute experiment scientists can used the observation.)

• c) Examination (This is the method of examine the patient with different diseases, for example, with using the different apparatuses.)

• d) Modeling

Rest membrane potentialRest membrane potential There is a potential difference across the membranes of most if not all cells,

with the inside of the cells negative to the exterior. By convention, this resting membrane potential (steady potential) is written with a minus sign,

signifying that the inside is negative relative to the exterior. Its magnitude vanes considerably from tissue to tissue, ranging from -9 to –100 mV. When 2 electrodes are connected through a suitable amplifier to a CRO and placed on the surface of a single axon, no potential difference is observed. However, if one electrode is inserted into the interior of the cell, a constant potential difference is observed, with the inside negative relative to the outside of the cell at rest. This resting membrane potential is found in almost all cells. In neurons, it is usually about –70 mV. .

 

 voltmeter

I-electrods

cell cell

Active transport of ionsActive transport of ions• There are two kind of ion’s transport: active and passive.

Active transport is doing due to the energy of ATP. The sodium-potassium pump responsible for the coupled active transport of Na+ out of cells and K+ into cells is a unique protein in the cell membrane. This protein is also an adenosine triphosphatase, ie, an enzyme that catalyzes the hydrolysis of ATP to adenosine diphosphate (ADP), and it is activated by Na+ and K+. Consequently, it is known as sodium-potassium-activated adenosine triphosphatase (Na+-K+ ATPase). The ATP provides the energy for transport. The pump extrudes three Na+ from the cell for each two K+ it takes into the cell, ie, it has a coupling ratio of 3/2.

•The origin of excitation•a) Characteristic of experimental stimulus (According to the force its divided on the under threshold, threshold and upper threshold.) •b) Characteristic of experimental stimulus (According to the nature its divided on chemical, mechanical, temperature, electrical)

Local answer, critical level of depolarization Local answer is arised only on under threshold stimulus.

Critical level of depolarization is the point from which the action membrane potential can developed.

 

ACTION POTENTIALACTION POTENTIAL1 – 1 – rest membrane potentialrest membrane potential; 2 – ; 2 – local responselocal response; 3 – ; 3 – Critical Critical levellevel of depolarization of depolarization; 4 – ; 4 – depolarizationdepolarization;; 5 – 5 –

repolarizationrepolarization; 6 – ; 6 – negative step potentialnegative step potential; 7 – ; 7 – positive step positive step potentialpotential

OuterMembrane

Inner

mV

Active potential Active potential (А) (А) and excitabilityand excitability (В) (В)

DepolarizationRepolarization

Negative step potential

Positive step potential

Latent addition

Absolute refractivity

3B - Relative refractivity4B - Exaltation

5B - Supernormal period

Carrying of excitation by axonsCarrying of excitation by axons

• a) Condition of carrying (1. Anatomic integrity of nerve‘s filament. 2. Physiological full value.)

• b) Laws of carrying (1. Double-sided conduction. 2. Isolated of conducting. 3. Conducting of excitation without attenuation.)

• c) Carrying in myelinated nerves (In myelin filaments conducting of excitation is doing from node of Ranvier to node of Ranvier.)

• d) Carrying in nonmyelinated nerves (In nonmyelin filaments conducting of excitation is doing uninterrupted.)

Common characteristic of chemical Common characteristic of chemical synapsessynapses

• Chemical synapses is the junctions in which the transmission of information do through the direct passage with chemical substances from cell to cell. These substances named mediators.

• Classification of chemical synapses • These synapses named for the type of

mediator – cholinergic (mediator – acetylcholine), adrenergic (mediator – epinephrine, nor epinephrine), serotonin (mediator – serotonin), dopaminergic (mediator – dopamine), GABA-ergic (mediator – gamma-amino butyric acid).

Chemical transmission of Chemical transmission of

synaptic activitysynaptic activity • Active membrane potential go along the

nerve to presynaptic end – presynaptic membrane have depolarilazed – the Ca2+-cannals activated – Ca2+-go to the presynaptic end – Ca2+-activated transport of vesiccles with the mediator along the neurofilaments to presynaptic membrane – the mediator pick out from presynaptic ends to the synaptic split – molecules of mediator diffuse through the synaptic split to postsynaptic membrane – molecules of mediator interact with the receptors on the postsynaptic membrane – this interaction lead to the conformation of receptors and activation of corresponding substances.

Common characteristic of electrical Common characteristic of electrical synapsessynapses

• Electrical synapses is the junctions in which the transmission of information do through the direct passage of bioelectrical signal from cell to cell. This synapses has small synaptic split (to 5 nm), low specific resistance between the presynaptic and postsynaptic membranes. There are the transverse canals in both membranes with the diameter of 1 nm.

• a) Excitatory transmitter (Excitatory impulses go to the synapse and increase permeability of postsynaptic cell membrane to Na+.)

• b) Inhibitory transmitter (Inhibitory impulses go to the synapse and increase permeability of postsynaptic cell membrane to Cl-, not to Na+.)

ElectromyographyElectromyographyActivation of motor units can be studied by electromyography, the process of recording the electrical activity of muscle on a cathode-ray oscilloscope. This may be done in humans by using small metal disks on the skin overlying the muscle as the pick-up electrodes or in un anesthetized humans or animals by using hypodermic needle electrodes. The record obtained with such electrodes is the electromyogramm (EMG). With needle electrodes, it is usually possible to pick up the activity of single muscle fibers.

Characteristic of skeletal musclesCharacteristic of skeletal muscles• Resting and active potentials of muscle fiber (The electrical events

in skeletal muscle and the ionic fluxes underlying them are similar to those in nerve, although there are quantitative differences in timing and magnitude. The resting membrane potential of skeletal muscle is about -90 mV. The action potential lasts 2-4 ms and is conducted along the muscle fiber at about 5 m/s. The absolute refractory period is 1-3 ms long and the after-polarizations, with their related changes in threshold to electrical stimulation, are relatively prolonged. The chronaxie of skeletal muscle is generally somewhat longer than that of nerve.

• Although the electrical properties of the individual fibers in a muscle do not differ sufficiently to produce anything resembling a compound action potential, there are slight differences in the thresholds of the various fibers. Furthermore, in any stimulation experiment, some fibers are farther from the stimulating electrodes than others. Therefore, the size of the action potential recorded from a whole muscle preparation is proportionate to the intensity of the stimulating current between threshold and maximal current intensities. The distribution of ions across the muscle fiber membrane is similar to that across the nerve cell membrane. As in nerve, depolarization is a manifestation of Na+ influx, and repolarization is a manifestation of K+ efflux.)

Solitary contractionSolitary contraction• The process by which the shortening of the contractile elements in muscle

is brought about is a sliding of the thin filaments over the thick filaments. The width of the A bands is constant, whereas the Z lines move closer together when the muscle contracts and farther apart when it is stretched. As the muscle shortens, the thin filaments from the opposite ends of the sarcomere approach each other; when the shortening is marked, these filaments apparently overlap.

• The sliding during muscle contraction is produced by breaking and re-forming of the crosslinkages between actin and myosin. The heads of the myosin molecules link to actin at an angle, produce movement of myosin on actin by swiveling, and then disconnect and reconnect at the next linking site, repeating the process in serial fashion. Each single cycle of attaching, swiveling, and detaching shortens the muscle 1 %.

• The immediate source of energy for muscle contraction is ATP. Hydrolysis of the bonds between the phosphate residues of this compound is associated with the release of a large amount of energy, and the bonds are therefore referred to as high-energy phosphate bonds. In muscle, the hydrolysis of ATP to adenosine diphosphate (ADP) is catalyzed by the contractile protein myosin; this adenosine triphosphatase (ATPase) activity is found in the heads of the myosin molecules, where they are in contact with actin.

• The process by which depolarization of the muscle fiber initiates contraction is called excitation-contraction coupling. The action potential is transmitted to all the fibrils in the fiber via the T system. It triggers the release of Ca2+ from the terminal cisterns, the lateral sacs of the sarcoplasmic reticulum next to the T system. The Ca2+ initiates contraction. Ca2+ initiates contraction by binding to troponin C. In resting muscle, troponin I is tightly bound to actin, and tropomyosin covers the sites where myosin heads bind to actin. Thus, the troponin-tropomyosin complex constitutes a “relaxing-protein” that inhibits the interaction between actin and myosin. When the Ca2+ released by the action potential binds to troponin C, the binding of troponin I to actin is presumably weakened, and this permits the tropomyosin to move laterally. This movement uncovers binding sites for the myosin heads, so that ATP is split and contraction occurs.

• Shortly after releasing Ca2+, the sarcoplasmic reticulum begins to reaccumulate Ca2+. The Ca2+ is actively pumped into longitudinal portions of the reticulum and diffuses from there to the cisterns, where it is stored. Once the Ca2+ concentration outside the reticulum has been lowered sufficiently, chemical interaction between myosin and actin ceases and the muscle relaxes. If the active transport of Ca2+ is inhibited, relaxation does not occur even though there are no more action potentials; the resulting sustained contraction is called a contracture. It should be noted that ATP provides the energy for the active transport of Ca2+ into the sarcoplasmic reticulum. Thus, both contraction and relaxation of muscle require ATP.

Connection between excitation and contractionConnection between excitation and contraction

• It is important to distinguish between the electrical and mechanical events in muscle. Although oneresponse does not normally occur without the other, their physiologic basis and characteristics are different. Muscle fiber membrane depolarization normally starts at the motor end-plate, the specialized structure under the motor nerve ending.

• A single action potential causes a brief contraction followed by relaxation. This response is called a muscle twitch; the action potential and the twitch are plotted on the same time scale. The twitch starts about 2 ms after the start of depolarization of the membrane, before repolanzation is complete. The duration of the twitch varies with the type of muscle being tested. “Fast” muscle fibers, primarily those concerned with fine, rapid, precise movement, have twitch durations as short as 7.5 ms. “Slow” muscle fibers, principally those involved in strong, gross, sustained movements, have twitch durations up to 100ms.

Summation of contraction and tetanus of musclesSummation of contraction and tetanus of muscles

• The electrical response of a muscle fiber to repeated stimulation is like that of nerve. The fiber is electrically refractory only during the rising and part of the falling phase of the spike potential. At this time, the contraction initiated by the first stimulus is just beginning. However, because the contractile mechanism does not have a refractory period, repeated stimulation before relaxation has occurred produces additional activation of the contractile elements and a response that is added to the contraction already present. This phenomenon is known as summation of contractions. The tension developed during summation is considerably greater than that during the single muscle twitch. With rapidly repeated stimulation, activation of the contractile mechanism occurs repeatedly before any relaxation has occurred, and the individual responses fuse into one continuous contraction. Such a response is called a tetanus (tetanic contraction). It is a complete tetanus when there is no relaxation between stimuli, and an incomplete tetanus when there are periods of incomplete relaxation between the summated stimuli. During a complete tetanus, the tension developed is about 4 times that developed by the individual twitch contractions.

• The stimulation frequency at which summation of contractions occurs is determined by the twitch duration of the particular muscle being studied. For example, if the twitch duration is 10 ms, frequencies less than 1/10 ms (100/s) cause discrete responses interrupted by complete relaxation, and frequencies greater than 100/s cause summation.

Peculiarities of smooth musclesPeculiarities of smooth muscles

• Resting membrane potential may be from –50 mV to –60 mV. In this process take place K+, Na+, Cl-. There are a large concentration of Na+, Cl- in the cells.

• Active potential (Prolongation of it may be from 20-50 ms to 1 second; amplitude is less that in skeletal muscles. Active potential end by after-hyperpolarization. The main role in the beginning of it have Ca+.)

• Elasticity, plasticity and tensility (Another special characteristic of smooth muscle is the variability of the tension it exerts at any given length. If a piece of visceral smooth muscle is stretched, it first exerts increased tension. However, if the muscle is held at the greater length after stretching, the tension gradually decreases. Sometimes the tension falls to or below the level exerted before the muscle was stretched. It is consequently impossible to correlate length and developed tension accurately, and no resting length can be assigned. In some ways, therefore, smooth muscle behaves more like a viscous mass than a rigidly structured tissue, and it is this property that is referred to as the plasticity of smooth muscle.

• The consequences of plasticity can be demonstrated in the intact animal. For example, the tension exerted by the smooth muscle walls of the bladder can be measured at varying degrees of distention. After each addition of fluid, the tension was measured for a period of time. Immediately after each increment of fluid, the tension was higher; but after a short period of time, it decreased.)

Characteristic of cardiac muscleCharacteristic of cardiac muscle• Resting membrane and action potential of cardiac muscle cells (The resting

membrane potential of individual mammalian cardiac muscle cells is about -80 mV (interior negative to exterior). Stimulation produces a propagated action potential that is responsible for initiating contraction. Depolarization proceeds rapidly and an overshoot is present, as in skeletal muscle and nerve, but this is followed by a plateau before the membrane potential returns to the baseline. In mammalian hearts, depolarization lasts about 2 ms, but the plateau phase and repolarization last 200 ms or more. Repolarization is therefore not complete until the contraction is half over.

• As in other excitable tissues, changes in the external K+ concentration affect the resting membrane potential of cardiac muscle, whereas changes in the external Na+ concentration affect the magnitude of the action potential. The initial rapid depolarization and the overshoot are due to a rapid increase in Na+ permeability similar to that occurring in nerve and skeletal muscle, whereas the second plateau phase is due to a slower starting, less intense, and more prolonged increase in Ca2+ permeability. The third phase is the manifestation of a delayed increase in K+ permeability. This increase produces the K+ efflux that completes the repolarization process. The Na+ channel in cardiac muscle is often called the fast channel. It probably has 2 gates, an outer gate that opens at the start of depolarization, at a membrane potential of -60 to -70 mV, and a second inner gate that then closes and precludes further influx until the action potential is over (Na+ channel inactivation). The Ca2+ channel is called the slow channel. It is activated at a membrane potential of -30 to -40 mV and inactivates much more slowly than the fast channel.

Mechanic propertiesMechanic properties• The contractile response of cardiac muscle begins just after

the start of depotanzation and lasts about 1,5 times as long as the action potential. The role of Ca2+ in excitation-contraction coupling is similar to its role in skeletal muscle, except that Ca2+ entering from the ECF as well as Ca2+ from the sarcoplasmic reticulum contributes to contraction. Responses of the muscle are all or none in character, ie, the muscle fibers contract fully if they respond at all. Since cardiac muscle is absolutely refractory during most of the action potential, the contractile response is more than half over by the time a second response can be initiated. Therefore, tetanus of the type seen in skeletal muscle cannot occur. Of course, tetanizalion of cardiac muscle for any length of time would have lethal consequences, and in this sense the fact that cardiac muscle cannot be tetanized is a safety feature. Ventricular muscle is said to be in the “vulnerable period” just at the end of the action potential, because stimulation at this time will sometimes initiate ventricular fibrillation.

ElectromyographyElectromyographyActivation of motor units can be studied by electromyography, the process of recording the electrical activity of muscle on a cathode-ray oscilloscope. This may be done in humans by using small metal disks on the skin overlying the muscle as the pick-up electrodes or in un anesthetized humans or animals by using hypodermic needle electrodes. The record obtained with such electrodes is the electromyogramm (EMG). With needle electrodes, it is usually possible to pick up the activity of single muscle fibers.

Types of ContractionTypes of Contraction

• Muscular contraction involves shortening of the contractile elements, but because muscles have elastic and viscous elements in series with the contractile mechanism, it is possible for contraction to occur without an appreciable decrease in the length of the whole muscle. Such a contraction is called isometric (“same measure” or length). Contraction against a constant load, with approximation of the ends of the muscle, is isotonic (“same tension”).

Summation of contraction Summation of contraction and tetanus of musclesand tetanus of muscles   

Active potential of cardiomyocytesActive potential of cardiomyocytesPhasePhase 0 0 ––depolarizationdepolarization;;

PhasePhase 1 1 –– rapid initial repolarizationrapid initial repolarization;; PhasePhase 2 2 – – plateauplateau;;

PhasePhase 3 3 –– rapid ending repolarizationrapid ending repolarization;; PhasePhase 4 4 –– restrest..