Smooth muscle cell: Difference between revisions
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Smooth muscle does not have [[Actin|actin]] and [[Myosin|myosin]] arranged into arrays like stirated muscle so appears uniformed under a microscope when stained. The content of myosin in smooth muscle cells is considerably less; the ratio of actin to myosin is about 15:1 whereas in striated skeletal muscle cells the ratio is 2:1. A smooth muscle cell is located within the walls of tubular or hollow organs or vessels for structural support. It is involved in physiologically substantial processes within the body including: regulation of blood flow through the vascular system; movement of the iris and expulsive actions of the urinary bladder and the uterus during childbirth. Smooth muscle cells have an elongated spindle shaped cell with a single [[Nuclei|nuclei]]. Smooth muscle contracts using the sliding filament mechanism, where [[Actin|actin]] and [[Myosin|myosin]] slide over each other. This mechanism requires energy which is provided by the hydrolysis of [[ATP|ATP]]. Instead of using troponins, which are used in skeletal muscle cell contraction, smooth muscle cell contraction is regulated by the calcium binding protein calmodulin. When there is an increase in calcium ion concentration, calmodulin attaches to caldesmon, which is an actin-binding protein. Caldesmon normally blocks the myosin-binding sites on actin filaments. As calmodulin attaches to caldesmon it releases actin, causing the myosin heads to bind to the actin filaments. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). [[Contraction|Contraction]] is initiated by calcium-regulated phosphorylation of myosin<ref>Walter F. Boron, E. L. (2009). Medical Physiology (2nd ed.). Philadelphia: Saunders Elsevier.</ref>. Apart from calcium ions, smooth muscle activity can also be regulated by external signalling molecules, for example, adrenaline. When adrenaline binds to the receptor and changes its shape, this in turns alters the structure of the G protein that binds to the receptor. This causes an increase of level of cyclic AMP inside the cell, which activates protein kinase. Protein kinase then phosphorylates and inactivates myosin light chain kinase, eventually leading to relaxation of the smooth muscle. Smooth muscle contraction is significantly slower than skeletal muscle contraction. It usually takes nearly a second whereas skeletal muscle takes a few millisecond<ref>Alberts, B. (2002). Molecular biology of the cell (4th ed.). New York: Garland Science.</ref>. | Smooth muscle does not have [[Actin|actin]] and [[Myosin|myosin]] arranged into arrays like stirated muscle so appears uniformed under a microscope when stained. The content of myosin in smooth muscle cells is considerably less; the ratio of actin to myosin is about 15:1 whereas in striated skeletal muscle cells the ratio is 2:1. A smooth muscle cell is located within the walls of tubular or hollow organs or vessels for structural support. It is involved in physiologically substantial processes within the body including: regulation of blood flow through the vascular system; movement of the iris and expulsive actions of the urinary bladder and the uterus during childbirth. Smooth muscle cells have an elongated spindle shaped cell with a single [[Nuclei|nuclei]]. Smooth muscle contracts using the sliding filament mechanism, where [[Actin|actin]] and [[Myosin|myosin]] slide over each other. This mechanism requires energy which is provided by the hydrolysis of [[ATP|ATP]]. Instead of using troponins, which are used in skeletal muscle cell contraction, smooth muscle cell contraction is regulated by the calcium binding protein calmodulin. When there is an increase in calcium ion concentration, calmodulin attaches to caldesmon, which is an actin-binding protein. Caldesmon normally blocks the myosin-binding sites on actin filaments. As calmodulin attaches to caldesmon it releases actin, causing the myosin heads to bind to the actin filaments. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). [[Contraction|Contraction]] is initiated by calcium-regulated phosphorylation of myosin<ref>Walter F. Boron, E. L. (2009). Medical Physiology (2nd ed.). Philadelphia: Saunders Elsevier.</ref>. Apart from calcium ions, smooth muscle activity can also be regulated by external signalling molecules, for example, adrenaline. When adrenaline binds to the receptor and changes its shape, this in turns alters the structure of the G protein that binds to the receptor. This causes an increase of level of cyclic AMP inside the cell, which activates protein kinase. Protein kinase then phosphorylates and inactivates myosin light chain kinase, eventually leading to relaxation of the smooth muscle. Smooth muscle contraction is significantly slower than skeletal muscle contraction. It usually takes nearly a second whereas skeletal muscle takes a few millisecond<ref>Alberts, B. (2002). Molecular biology of the cell (4th ed.). New York: Garland Science.</ref>. | ||
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Revision as of 01:09, 28 November 2014
Smooth muscle does not have actin and myosin arranged into arrays like stirated muscle so appears uniformed under a microscope when stained. The content of myosin in smooth muscle cells is considerably less; the ratio of actin to myosin is about 15:1 whereas in striated skeletal muscle cells the ratio is 2:1. A smooth muscle cell is located within the walls of tubular or hollow organs or vessels for structural support. It is involved in physiologically substantial processes within the body including: regulation of blood flow through the vascular system; movement of the iris and expulsive actions of the urinary bladder and the uterus during childbirth. Smooth muscle cells have an elongated spindle shaped cell with a single nuclei. Smooth muscle contracts using the sliding filament mechanism, where actin and myosin slide over each other. This mechanism requires energy which is provided by the hydrolysis of ATP. Instead of using troponins, which are used in skeletal muscle cell contraction, smooth muscle cell contraction is regulated by the calcium binding protein calmodulin. When there is an increase in calcium ion concentration, calmodulin attaches to caldesmon, which is an actin-binding protein. Caldesmon normally blocks the myosin-binding sites on actin filaments. As calmodulin attaches to caldesmon it releases actin, causing the myosin heads to bind to the actin filaments. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). Contraction is initiated by calcium-regulated phosphorylation of myosin[1]. Apart from calcium ions, smooth muscle activity can also be regulated by external signalling molecules, for example, adrenaline. When adrenaline binds to the receptor and changes its shape, this in turns alters the structure of the G protein that binds to the receptor. This causes an increase of level of cyclic AMP inside the cell, which activates protein kinase. Protein kinase then phosphorylates and inactivates myosin light chain kinase, eventually leading to relaxation of the smooth muscle. Smooth muscle contraction is significantly slower than skeletal muscle contraction. It usually takes nearly a second whereas skeletal muscle takes a few millisecond[2].