Sliding filament model of muscle contraction
Skeletal muscle shortens during contraction because thick and thin filaments slide past one another, mechanism known as sliding filament mechanism of muscle contraction.
When muscle contracts, actin is pulled along myosin towards center of sarcomere, until actin and myosin filaments are completely overlapped.
H zone becomes smaller and smaller due to increasing overlap of actin and myosin filaments, and muscle shortens.
When muscle fully contracted H zone is no longer visible.
As muscle contracts;
1. Z discs come closer together
2. Width of I Bands decreases
3. Width of H zones decreases
4. No change in width of A band.
Arrangement of myosin and actin molecules in myofilaments is important to mechanism of muscle contraction.
Process;
Actin filament (thin) made up of actin, tropomyosin, troponin.
Myosin filament (thick) made up of myosin molecule that have oval shaped heads and long tails.
Muscle action potential traveling along T- tubules open Ca2+ release channels in SR, which allows calcium ions to flood into sarcoplasm.
Ca2+ binds to troponin in actin filament, and then binding site for myosin head.
Use ATP, myosin heads bind to actin, actin filament are pulled toward center of sarcomere.
Energy is used to move myosin heads towards the actin filaments.
Myosin and actin myofilaments slide past each other, toward H zone.
Width of A band is unchanged but the I band shortens and Z lines move closer together.
A microfilament slides, cross bridge detach from one site and attach to other next site.
Muscle contraction remains as long as Ca2+ is abundant in sarcoplasm, and also if ATP is available.
During process of muscle contraction, calcium is actively pumped back into sarcoplasmic reticulum.
Muscle relaxes when Ca2+ level decreases because tropomyosin changes back to it's previous state.
Muscle
A bundle of fibrous tissue in human or animal body ability to contract producing movement in or maintaining the position of parts of body.
Muscle cells contains protein filament of actin and myosin that slide past one another producing a contraction that changes both length and shape of cell. Muscle function to produce force and motion.
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