PHYSIOLOGY AS A SCIENCE.

BIOELECTRICAL PHENOMENON IN NERVOUS

CELLS.

DETERMINATION OF “PHYSIOLOGY” NOTION. PHYSIOLOGICAL 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. Pathophysiology.

Methods 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) Simulation

Resting 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 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 excitationa) 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 POTENTIAL1 – rest membrane potential; 2 – local response; 3 – Critical level of depolarization; 4 – depolarization; 5 – repolarization; 6 – negative step potential; 7 – positive step potential

OuterMembrane

Inner

mV

Active potential (А) and excitability (В)

DepolarizationRepolarization

Negative step potential

Positive step potential

Latent addition

Absolute refracterity

3B - Relative refracterity4B - Excaltation

5B - Supernormal period

Carrying 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 synapses

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), dopaminenergic (mediator – dopamine), GABA-ergic (mediator – gamma-amino butyric acid).

Chemical transmission of synaptic 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 synapses

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+.)

ElectromyographyActivation 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 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 and tetanus of muscles  

Active potential of cardiomyocytesPhase 0 –depolarization; Phase 1 – rapid initial repolarization; Phase 2 – platou; Phase 3 – rapid ending repolarization; Phase 4 – rest.