Plan
► Basic physiological properties of tissues. Concept of excitable tissue.
► Excitability of tissues and methods of its evaluation.
► Lability of tissues. Measure of lability.
► States of excitable tissues: relative physiological rest and active state.
This is the first lecture of one of the most complicated sections of physiology - physiology of excitable tissues. This section is very important because it provides understanding of fundamentals of physiology:
► physiological properties of cells and tissues;
► states of cells and tissues;
► processes occurring in cells and tissues.
It should be noted that in these discussions we will use concepts and regularities of cell and tissue levels. On the systemic and, moreover, on organism levels different concepts and regularities exist.
Physiological Properties of Tissues. Concept of Excitable
Tissues
A property is understood as a permanent characteristics of an object. Physiological properties include irritability, excitability, conductibility, lability, contractility and an ability to secretion.
Irritability is an ability of a tissue to change metabolism under stimulation. The property of irritability is that what distinguishes objects of organic nature from those of inorganic nature.
Excitability of Tissues and Methods of its Evaluation
The property of excitability is inherent only to three kinds of body tissues: muscular, nervous and glandular tissues. Excitability is understood as
an ability of excitable tissues to respond to stimuli by development of excitation in the form of a specific response and a bioelectrical process. Excitability is characterized by two parameters: threshold of excitability and latent period of excitation.
Threshold of excitability is the minimum force of stimulus required to produce excitation in an excitable structure (cell or tissue). The lower the threshold of excitability, the higher the excitability, that is, threshold of excitability and excitability are inversely proportional.