However, a low concentration of calcium remains in the sarcoplasm to maintain muscle tone. Muscle contraction continues until ATP-dependent calcium pumps actively transport Ca ++ ions back into the SR and out of the cell. The influx of extracellular Ca ++ ions, which diffuse into the sarcoplasm to reach the calmodulin, accounts for most of the Ca ++ that triggers contraction of a smooth muscle cell. Smooth muscle fibers have a limited calcium-storing SR but have calcium channels in the sarcolemma (similar to cardiac muscle fibers) that open during the action potential along the sarcolemma. T-tubules are not required to reach the interior of the cell and therefore not necessary to transmit an action potential deep into the fiber. This arrangement causes the entire muscle fiber to contract in a manner whereby the ends are pulled toward the center, causing the midsection to bulge in a corkscrew motion ( ).Īlthough smooth muscle contraction relies on the presence of Ca ++ ions, smooth muscle fibers have a much smaller diameter than skeletal muscle cells. When the thin filaments slide past the thick filaments, they pull on the dense bodies, structures tethered to the sarcolemma, which then pull on the intermediate filaments networks throughout the sarcoplasm. The thin filaments also are anchored to the dense bodies the structures invested in the inner membrane of the sarcolemma (at adherens junctions) that also have cord-like intermediate filaments attached to them. The heads can then attach to actin-binding sites and pull on the thin filaments. The Ca ++-calmodulin complex then activates an enzyme called myosin (light chain) kinase, which, in turn, activates the myosin heads by phosphorylating them (converting ATP to ADP and P i, with the P i attaching to the head). In a smooth muscle fiber, external Ca ++ ions passing through opened calcium channels in the sarcolemma, and additional Ca ++ released from SR, bind to calmodulin.
Calcium ions are supplied by the SR in the fibers and by sequestration from the extracellular fluid through membrane indentations called calveoli.īecause smooth muscle cells do not contain troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but instead by the regulatory protein calmodulin. A dense body is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma.
These thin filaments are anchored by dense bodies. Although they do not have striations and sarcomeres, smooth muscle fibers do have actin and myosin contractile proteins, and thick and thin filaments. Smooth muscle fibers are spindle-shaped (wide in the middle and tapered at both ends, somewhat like a football) and have a single nucleus they range from about 30 to 200 μm (thousands of times shorter than skeletal muscle fibers), and they produce their own connective tissue, endomysium. So we can see that this is our answer for institution and for that correct option.View the University of Michigan WebScope to explore the tissue sample in greater detail. So this is the answer of are given fusion as you can say that when this particular is moving in a circular motion with the speed of the there is a tension in the string and this tension force is equal to this is centripetal force. So we can see dead note force on particle directed towards center is owned by it is equal to centripetal force which is equal to tension in the string, the sequel to attention And this is equals two. So went a particle is moving a circle that requires centripetal force is given by obtained from the tension in the string that is obtained from tension in the screen. Let this is a particular which is moving in there Circular motion that is the motion of the 3rd particular and the mouth of the particularly given to us. If the particle moves in a circular motion with the speed we then we have to find net 4th on the particle towards the center. Is connected to a particular Masum and other other to a small pack on a smooth original table. In this question we have given that one end of a string of length L.
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