List and briefly describe the mechanisms for smooth muscle
contraction in terms of altering (increasing) the...
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List and briefly describe the mechanisms for smooth musclecontraction in terms of altering (increasing) the force ofcontraction.
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Mechanism Smooth muscle contraction is dependent on calcium influx Calcium is increased within the smooth muscle cell through two different processes First depolarization hormones or neurotransmitters cause calcium to enter the cell through Ltype channels located in the caveolae of the membrane Intracellular calcium then stimulates the release of calcium from the sarcoplasmic reticulum SR by way of ryanodine receptors and IP3 this process is referred to as calciuminduced calcium releaseUnlike skeletal muscle smooth muscle calcium release from the sarcoplasmic reticulum is not physically coupled to the ryanodine receptor Once calcium has entered the cell it is free to bind calmodulin which transforms into activated calmodulin Calmodulin then activates the enzyme myosin light chain kinase MLCK MLCK then phosphorylates a regulatory light chain on myosin Once phosphorylation has occurred a conformational change takes place in the myosin head this increases myosin ATPase activity which promotes interaction between the myosin head and actin Crossbridge cycling then occurs and tension is generated The tension generated is relative to the amount of calcium concentration within the cell ATPase activity is much lower in smooth muscle than it is in skeletal muscle This factor
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