10 topics with brief reviews: definitions, key facts, and class questions.
This section is dedicated to the biophysics and physiology of muscle contraction — the process responsible for movement, breathing, and maintaining the tone of internal organs. Here, we break down how a nerve impulse is transformed into mechanical work.
You will study the basic properties and functions of skeletal muscles, the structural organization of motor units, and the types of muscle fibers. We will cover the types of muscle contractions, summation mechanisms, tetanus formation, and the specifics of smooth muscle contraction. Special attention is paid to the molecular sliding filament mechanism, energetics, causes of muscle fatigue, and the concept of lability in excitable tissues.
Pay special attention: during practical classes and colloquia, students are most frequently asked to describe in detail the molecular cycle of actin-myosin cross-bridges, draw and explain graphs of fused and unfused tetanus, and substantiate the optimum load law.
Its measure is the maximum stimulation frequency to which the tissue responds by generating impulses without transforming the initial rhythm.
What determines phasic and tonic muscle contractions?
The pattern of muscle contractions is entirely determined by the predominant fiber type. Fast white fibers are responsible for phasic contractions, while slow red fibers handle tonic ones.
Why does a whole muscle not obey the "all-or-none" law?
Because an intact muscle consists of many muscle fibers, each of which has its individual excitation threshold. When stimulus strength increases, a larger number of fibers are excited, leading to a smooth increase in contraction amplitude.
How does an isotonic contraction differ from an isometric one?
During isotonic contraction, the muscle shortens while tone remains constant, whereas during isometric contraction, the length stays the same while muscle tension increases significantly.
How does fused tetanus differ from unfused tetanus?
Fused tetanus occurs when a stimulus falls during the shortening period (complete fusion without relaxation). Unfused tetanus occurs when it falls during the relaxation period, resulting in visible "notches" of partial tension drop on the graph.
What is included in a single motor unit?
A motor unit consists of exactly one nerve fiber and all the muscle fibers it directly innervates.
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