From Big Medical Encyclopedia

TETANUS (tetanus; Greek tetanos a tension, tension, a spasm) — is long the proceeding reduction of a muscle as a result of summation of its single reductions following one after another arising at rhythmic impact of irritations on it.

At animals and the person tetanic reductions of skeletal muscles provide various forms of locomotion.

In pathology the term «tetanus» designate the disease caused by a tetanic stick (see. Tetanus ).

At irritation of a nerve or directly muscles there is a reduction of myofibrils of muscle fiber (see. Muscles ). As a result the wave of reduction, i.e. shortening of a muscle and increase in muscular tension develops (see. Muscular contraction ). When the interval between irritations (the arriving nervous impulses) is less than duration of single reduction of a muscle, single sokratitelny waves are imposed at each other summed up) therefore there is a tetanic reduction, or a muscular tetanus. Duration and force of T. can be much more, than at single reduction of a muscle. Its form depends on a ratio between the frequency of irritation and duration of a single wave of reduction. At irritation of not completely relaxed muscle the T is observed so-called incomplete, or gear. At the rhythmic irritations which are very pulled together in time when the interval between them is shorter than the period of activity of a sokratitelny aiparat of a muscle, there is conjoint, or smooth, a T., to-ry it is characterized by continuous long shortening of a muscle, H. E. Vvedensky., explaining the mechanism fiziol. labilities (see), showed that height of T. considerably varies depending on force and the frequency of irritation. There are optimum frequency and power of irritation, at to-rykh T. the greatest. At very strong and frequent irritations height of T. the T is much lower expected, and itself. less constant. Frequency of an impulsation for receiving smooth T. it is various for various muscles and muscle fibers and is defined by duration of their single wave of reduction. In most cases tetanic reductions of separate muscle fibers proceed asynchronously, however at considerable muscular efforts synchronization of their activity is possible. Mechanical reduction of muscle fibers results from passing through a neuromuscular synapse of a series of single excitation waves and emergence in a muscle of action potentials (see. Bioelectric potential ). At tetanic reductions and continuous T. these potentials proceed separately; with increase in frequency of irritation their frequency and amplitude increases, but they do not merge. The main patterns of emergence of tetanic reductions are studied in experiments on the isolated muscles. Under natural conditions existence of an organism amplitude of reduction of skeletal muscles is defined by hl. obr. quantity of the neuromotor units involved in activity.

See also Tetany .

Bibliography: Vvedensky N. E.; Complete works, t. 2, L., 1951; Zhukov E. K. Sketches on neuromuscular physiology, L., 1969; Ukhtomsky A. A. Collected works, t. 3, L., 1952; To r liger P. Tetanus und Tonus der guergesfreifen Skelettmuskeln der Wirbeltiere und des Menschen, Lpz., 1952; Rosenblueth A. Rubio R. Tetanic summation in isotonic and isometric responses, Arch. int. Physiol., v. 68, p. 165, 1960.

E. L. Golubeva.