Skeletal muscles contraction

FIGURE 17.23 The mechanism of skeletal muscle contraction. The free energy of ATP hydrolysis drives a conformational change in the myosin head, resulting in net movement of the myosin heads along the actin filament. Inset) A ribbon and space-filling representation of the actin—myosin interaction. (SI myosin image courtesy of Ivan Rayment and Hazel M. Holden, University of Wiseonsin, Madison.)... 

Botulinum neurotoxins are widely used as therapeutic agents to cause reduction or paralysis of skeletal muscle contraction. They are used to treat cervical dystonia, which causes regional involuntary muscle spasms often associated with pain. Moreover, they are used in strabism, blepharospasm, hemifacial spasm, and... 

Dihydropyridine receptor (DHPR) is a member of voltage-dqiendent Ca2+ channels (CaVi, L-type), which specifically binds to dihydropyridine derivatives, a group of the Ca2+ channel blockers. Cav 1.1 works as the voltage sensor for skeletal muscle contraction, and Cay 1.2, as Ca2+-influx channel for cardiac muscle contraction. 

Thus, Ca " controls skeletal muscle contraction and relaxation by an allosteric mechanism mediated by TpC, Tpl, TpT, tropomyosin, and F-actin. 

More than 99% of total body calcium is found in bone the remaining less than 1% is in the ECF and ICE Calcium plays a critical role in the transmission of nerve impulses, skeletal muscle contraction, myocardial contractions, maintenance of normal cellular permeability, and the formation of bones and teeth. There is a reciprocal relationship between the serum calcium concentration (normally 8.6 to 10.2 mg/dL [2.15 to 2.55 mmol/L]) and the serum phosphate concentration that is regulated by a complex interaction between parathyroid hormone, vitamin D, and calcitonin. About one-half of the serum calcium is bound to plasma proteins the other half is free ionized calcium. Given that the serum calcium has significant protein binding, the serum calcium concentration must be corrected in patients who have low albumin concentrations (the major serum protein). The most commonly used formula adds 0.8 mg/dL (0.2 mmol/L) of calcium for each gram of albumin deficiency as follows ... 

Describe the sliding filament theory of skeletal muscle contraction... 

Describe the factors that influence the strength of skeletal muscle contraction including multiple motor unit summation, asynchronous motor unit summation, frequency of nerve stimulation, length-tension relationship, and diameter of the muscle fiber... 

All types of muscle require calcium for contraction. In skeletal muscle, Ca++ ions are stored within an extensive membranous network referred to as the sarcoplasmic reticulum. This network is found throughout the muscle fiber and surrounds each myofibril. Furthermore, segments of the sarcoplasmic reticulum lie adjacent to each T tubule that, with a segment of sarcoplasmic reticulum on either side of it, is referred to as a triad. As the action potential is transmitted along the T tubule, it stimulates the release of Ca++ ions from the sarcoplasmic reticulum. The only source of calcium for skeletal muscle contraction is the sarcoplasmic reticulum. 

The mechanism of skeletal muscle contraction is described by the Sliding Filament Theory (see Figure 11.2). This mechanism begins with the "priming ... 

Number of muscle fibers contracting. As the number of contracting muscle fibers increases, the strength of skeletal muscle contraction increases. Two major factors determine the number of muscle fibers activated at any given... 

Skeletal muscle activity. In the extremities (arms and legs), many veins lie between the skeletal muscles. Contraction of these muscles causes compression of the veins and an increase in venous pressure. This external... 

The answer is d. (Hardman, pp 142—M3.) ACh will stimulate both muscarinic and nicotinic receptors. Skeletal muscle contraction is mediated through NM receptors, and ganglionic stimulation is an effect of NN receptors All of the other effects listed in the question occur following muscarinic receptor activation and will be blocked by atropine and scopolamine, both of which are muscarinic receptor antagonists. Skeletal muscle contraction will not be affected by these drugs rather, a neuromuscular blocker (e.g., tubocurarine) is required to antagonize this effect of ACh. 

Zot, A. S. and Potter, J. D. Structural aspects of troponin-tropomyosin regulation of skeletal muscle contraction. Annu. Rev. Biophys. Biophys. Chem. 16 535-560,1987. 

In contrast, skeletal muscle contraction is more rapid than that of smooth muscle but skeletal muscle cannot maintain the same tone for long periods of time. As indicated in Table 7.1, we can distinguish sub-types of muscle fibre within... 

Muscle spindles are composed of nuclear bag (dynamic) and chain (static) fibres known as intrafusal fibres and these are innervated by y motor neurones. Extrafusal fibres make up the muscle bulk and are innervated by a motor neurones. Stimulation of the muscle spindle leads to increased skeletal muscle contraction, which opposes the initial stretch and maintains the length of the fibre. This feedback loop oscillates at 10 Hz, which is the frequency of a physiological tremor. 

Figure 5.14 Schematic diagram showing interaction of thick and thin filaments in skeletal muscle contraction. (Adapted from Stryer, 1975.)...

It has been postulated that 2-PAM exerts its cardiac action in rabbit atria through its alteration of calcium metabolism. The relaxation phase of skeletal muscle contraction seems to be directly affected by the sarcoplasmic reticulum because of its ability to sequester calcium actively.29,46 a similar role has been suggested for the sarcoplasmic reticulum in cardiac muscle. 6,83 The onset of muscle contraction takes place when calcium reaches a crit-cal concentration. This contraction is later reduced by the increased calcium-sequestering activity of the sarcoplasmic reticulum. Thus, 2-PAM can affect this process by decreasing the rate of calcium uptake by the sarcoplasmic reticulum, which results in increasing the time required to reduce the calcium concentration enough to allow relaxation to take place. This was demonstrated by the Increase in the relaxation phase. It was suggested that this... 

HT2 receptors are present on skeletal muscle membranes, but their physiologic role is not understood. Serotonin syndrome is a condition associated with skeletal muscle contractions and precipitated when MAO inhibitors are given with serotonin agonists, especially antidepressants of the selective serotonin reuptake inhibitor class (SSRIs see Chapter 30). Although the hyperthermia of serotonin syndrome results from excessive muscle contraction, serotonin syndrome is probably caused by a central nervous system effect of these drugs (Table 16-4 and Serotonin Syndrome and Similar Syndromes). 

Contraction-relaxation processes in muscle proceed by a sliding filament mechanism, whereby actin and myosin filament move relative to one another. The reaction is energized by ATP and regulated by the level of calcium ions. In vertebrate skeletal muscle contraction is controlled by the interaction of calcium ions with the specific protein troponin which is attached to the actin filaments, whereas among many invertebrates troponin is lacking and myosin and not actin is controlled192. However, in a few invertebrates both types of filaments are involved in regulation. 

Adhikari BB, Wang K. 2001. S100A1 modulates skeletal muscle contraction by desensitizing calcium activation of isometric tension, stiffness and ATPase. FEBS Lett 497(2, 3) 95-98. 

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