General properties, membrane potentials, laws of stimulation, excitability, and inhibition
7 topics with concise reviews: definitions, key facts, and class questions.
This section forms the foundation of normal physiology. Here we examine the general properties of living organisms, the principles of physiological regulation, and how cells generate electrical signals. You will learn why the resting membrane potential arises and how it transitions into an action potential or local excitation (local response).
The material covers the classic laws of stimulation of excitable tissues, as well as the states of optimum, pessimum, and parabiosis (based on the teachings of N.E. Vvedensky), which describe tissue responses to rhythmic stimuli. Special attention is paid to inhibition—an active process essential for the proper coordination of bodily functions.
During colloquia and exams, professors most frequently ask you to draw an action potential graph aligned with ionic currents, explain the differences between a local response and full-fledged excitation, and detail the phases of parabiosis. Without a solid grasp of these topics, further study of the nervous and muscular systems is impossible.
What is the difference between trigger and selective irritability?
Trigger irritability does not depend on the quality of the stimulus—it merely initiates a reaction like a trigger mechanism. Selective irritability operates in a strictly specific "lock-and-key" manner via protein receptors.
Which ions make the main contribution to the creation of the resting potential?
Potassium ($K^+$) ions play the main role. It is their passive exit from the cell along the concentration gradient and subsequent electrostatic attraction that create the potential difference across the membrane.
What is the role of the sodium-potassium pump during spike generation?
The pump itself does not participate in the fast phases of depolarization and repolarization. Its task is to restore the initial ion concentrations after the action potential has already completed.
Why does local excitation not obey the "all-or-none" law?
Because its amplitude changes: the stronger the applied subthreshold stimulus, the higher the amplitude of the local response will be.
What does chronaxie indicate?
Chronaxie indicates the minimum duration of a stimulus with a strength of two rheobases at which the tissue is excited. This is a more accurate and stable indicator of excitability than the rheobase.
What is the main criterion for assessing tissue excitability?
The primary measure is the stimulation threshold — the minimum impact strength capable of eliciting a propagating action potential. The relationship is inversely proportional: the lower the threshold, the higher the cell's excitability.
Master the entire topic in the "Physiology" course
This is a summary. The course covers everything tested in classes and exams.
4,128 pages of study guides covering all topics
Assignments and quizzes after every topic — just like in a colloquium