November 4 Lecture - November 4, 2008 Review Structure of...

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November 4, 2008 Review Structure of Skeletal Muscle Whole Muscle Muscle Fibre Enlarged Muscle Fibre Myofibril Myofilaments Muscle Contraction In order for sarcomere to function, other accessory structures must be present - Sarcoplasmic reticulum: network of filamentous sacs that surround the surface of each myofibril o The tube components within this are the t- tubule (or transverse tubule). T-tubules occur at each z line T-tubules penetrate from the sarcolemma (the membrane of the muscle fibre) and are oriented at 90 degree angels into the muscle fibre making contact with every sarcomere along the length of the myofibril Revealled by electromicroscopy Function: to make contact with internal sarcomere and the outside of the cell or fibre When muscle is stimulated via electrical current, current travels along cell membrane and covers entire length of the cell. Penetrates into interior of the fibre, activating the myofibrils in the fibre and activates the sarcomere along the length of the fibre. T-tubules facilitate a means for the current to reach the functional units of the fibre. Making contact with the sarcoplasmic reticulum, radiating outwards and here is where an important link is made between the contractile stimulus and the myofibrils Lateral sacs contains calcium ions, when current reaches these it prompts the release of these calcium ions which activate the contractile activity within the sarcomere. Electrical stimulus activates calcium release via travelling through t- tubules in the filaments Calcium release (muscle contraction) halts and reabsorbed into sarcoplasmic reticulum (muscle relaxation) - During contraction, the A-band remains a constant length - I band decreases in length quite noticeably - As contraction continues, H zone will ultimately disappear - Actual length of the actin filaments remains constant despite decrease in I band o Discovered by H.E. Huxley and A.F. Huxley o In 1954, came up with a theory as to how muscle contracts During contraction process, there was a reorganization of actin and myosin filaments. Actin filaments slid inwardly past the myosin filaments until the actin filaments touched (the point of full contraction of the muscle). Called the sliding filament theory (or interdigitation theory). Process of muscle contraction has been observed many times since, and this is the premise that we understand muscle to function. - Knob-like structures extend off myosin filaments toward actin filaments, known as cross bridges that link the actin and myosin filaments.
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o Points of contact between actin and myosin filaments, now know that it is these points of contact that provides the means by which the actin filaments are drawn in to the centre of the A band during contraction - Each sarcomere has minimal movement overall during contraction (due to its small size), however thousands are present so a substantial shortening of tissue as a whole is quite
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This note was uploaded on 10/23/2011 for the course BIOL 2125 taught by Professor Dr.park during the Winter '02 term at A.T. Still University.

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November 4 Lecture - November 4, 2008 Review Structure of...

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