Cramp a painful spasm tic involuntary twitching of

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Cramp - a painful spasm Tic - involuntary twitching of muscles normally under voluntary control - eyelid or facial muscles Tremor - rhythmic, involuntary contraction of opposing muscle groups
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Abnormal Contractions Contractures can occur for many reasons, such as paralysis, muscular atrophy, and forms of muscular dystrophy. Fundamentally, the muscle and its tendons shorten, resulting in reduced flexibility.
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Additional Information The following eight slides are from another source and are here for your benefit, in an attempt to help you better understand the processes of skeletal muscle fiber contraction.
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Excitation (steps 1 & 2) Nerve signal stimulates voltage-gated calcium channels that result in exocytosis of synaptic vesicles containing ACh
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Excitation (steps 3 & 4) Binding of ACh opens Na+ and K+ channels resulting in an end-plate potential (EPP)
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Excitation (step 5) Voltage change in end-plate region (EPP) opens nearby voltage-gated channels in plasma membrane producing an action potential
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Excitation-Contraction Coupling (steps 6 & 7) Action potential spreading over sarcolemma reaches T tubules -- voltage-gated channels open in T tubules causing calcium gates to open in SR
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Excitation-Contraction Coupling (steps 8 & 9) Calcium release causes binding of myosin to active sites on actin
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Contraction (steps 10 & 11) Myosin head with an ATP molecule bound to it can form a cross-bridge (myosin ATPase releases the energy allowing the head to move into position)
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Contraction (steps 12 & 13) Power stroke shows myosin head releasing the ADP & phosphate and flexing as it pulls thin filament along -- binding of more ATP releases head from the thin filament
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Relaxation (steps 14 & 15) Stimulation ceases and acetylcholinesterase removes ACh from receptors so stimulation of the muscle cell ceases
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Relaxation (step 16) Active transport pumps calcium back into SR where it binds to calsequestrin ATP is needed for muscle relaxation as well as muscle contraction
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Relaxation (steps 17 & 18) Loss of calcium from sarcoplasm results in hiding of active sites and cessation of the production or maintenance of tension
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