Twitching

The cells of the latter three types contain only a single nucleus and are called myocytes. The cells of skeletal muscle are long and multinucleate and are referred to as muscle fibers. At the microscopic level, skeletal muscle and cardiac muscle display alternating light and dark bands, and for this reason are often referred to as striated muscles. The different types of muscle cells vary widely in structure, size, and function. In addition, the times required for contractions and relaxations by various muscle types vary considerably. The fastest responses (on the order of milliseconds) are observed for fast-twitch skeletal... 

Using the values in Table 24.1 for body glycogen content and the data in part b of the illustration for A Deeper Look (page 759), calculate the rate of energy consumption by muscles in heaty exercise (in J/sec). Use the data for fast-twitch muscle. 

Ziehen, n. drawing, etc. (see ziehen) draft, traction (of liquids) ropiness move twinge, twitch, -lassen, n. drawing, infusion (as of tea) allowing (a vessel) to fill, filling. Zieh-fkhigkeit, /. capability of being drawn, pulled, etc. (see ziehen) (Metal.) draw-... 

Parvalbumin (Fig 1) is a cytosolic protein expressed in fast-twitch skeletal muscles and in the nervous system. In muscles, parvalbumin controls the relaxation process. In the CNS, parvalbumin, expressed in a subpopulation of GABAergic neurons, is correlated with their firing rates, protecting the cells from Ca2+ overload. 

Isaacs syndrome (an acquired neuromyotonia) is caused by autoantibodies directed against 4-aminopyr-idine or a-dendrotoxin-sensitive K+ channels (Kvl.l and Kvl.6) in motor and sensory neurons. The syndromes include muscle twitching during rest, cramps during muscle contraction, impaired muscle relaxation, and muscle weakness due to hyperexcitability of peripheral motor nerves. 

Tissue-Specific Expression. In adult rodents, PPAR.a is expressed in liver, kidney, intestine, heart, skeletal muscle, retina, adrenal gland, and pancreas. In adult human, PPARa is expressed in the liver, heart, kidney, large intestine, skeletal muscle (mostly slow-twitch oxidative type I fibers), and in cells of atherosclerotic lesions (endothelial cells, smooth muscle cells, and monocytes/macrophages). Therefore, regardless of... 

In sympathetically innervated tissues, such as vas deferens or blood vessels, ATP produces fast responses mediated by P2X receptors followed by a slower component mediated by G protein-coupled a-adrenoceptors (Fig. 2) NPY usually acts as a pre-or postjunctional modulator of the release and/or action of NA and ATP. Similarly, for parasympathetic nerves supplying the urinary bladder, ATP provokes a fast, short-lasting twitch response via P2X receptors, whereas the slower component is mediated by G... 

Twitch is a muscle contraction caused by a single action potential, whereas tetanus is a sustained muscle contraction caused by a series of repetitive action potentials. The amplitude of tetanus contraction is larger than that of twitch, due to mechanical summation. 

Neurotoxicity (damage to the nervous system by a toxic substance) may also be seen with the administration of the aminoglycosides. Signs and symptoms of neurotoxicity include numbness, skin tingling, circum-oral (around the mouth) paresthesia, peripheral paresthesia, tremors, muscle twitching, convulsions, muscle weakness, and neuromuscular blockade (acute muscular paralysis and apnea). 

MONITORING FOR NEUROTOXICITY. The nurse should be alert for symptoms such as numbness or tingling of the skin, circumoral paresthesia, peripheral paresthesia (numbness or tingling in the extremities), tremors, and muscle twitching or weakness. The nurse reports any... 

Mydriasis, tachycardia, twitching, tremor, restlessness, irritability, anxiety, anorexia... 

Skeletal muscle contains three types of fiber fast-twitch oxidative glycolytic (type 2A), fast-twitch glycolytic (type 2B), and slow-rwitch oxidative fibers (type 1). The proportion of each fiber type varies in different muscles. Different fiber types contain different isoforms of myosin, although there is no evidence that their mitochondria differ qualitatively. It has been reported that there are differences between subsarcolemmal mitochondria and those deeper in the same fiber but this has been questioned (see Sherratt et al., 1988 for references). 

Figure 2. Muscle stimulation, a) a single nerve impulse (stimulus) causes a single contraction (a twitch). There is a small delay following the stimulus before force rises called the latent period, b) A train of stimuli at a low frequency causes an unfused tetanus. Force increases after each progressive stimulus towards a maximum, as calcium levels in the myofibrillar space increase. But there is enough time between each stimulus for calcium to be partially taken back up into the sarcoplasmic reticulum allowing partial relaxation before the next stimulus occurs, c) A train of stimuli at a higher frequency causes a fused tetanus, and force is maximum. There is not enough time for force to relax between stimuli. In the contractions shown here, the ends of the muscle are held fixed the contractions are isometric.

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