Sliding filament theory
Say it: SLY-ding FIL-uh-ment THEER-ee
The sliding filament theory is the model of muscle contraction in which thin actin filaments slide past thick myosin filaments, shortening each sarcomere.
Also: sliding filament model, sliding filament hypothesis, sliding filament mechanism
Definition
What is the sliding filament theory?
The sliding filament theory is the accepted explanation of how striated muscle, both skeletal and cardiac, contracts. It was put forward in 1954 in two papers printed side by side, one by Hugh Huxley and Jean Hanson and the other by Andrew Huxley and Rolf Niedergerke. Their key insight was that the filaments themselves do not shorten; instead, thin filaments of actin slide over thick filaments of myosin toward the middle of each sarcomere, the repeating unit of a muscle fiber.
Contraction begins when a nerve signal releases calcium ions from the sarcoplasmic reticulum. Calcium binds troponin, which shifts tropomyosin away from the binding sites on actin. Myosin heads then attach to actin, forming cross-bridges, and pivot in a power stroke that drags the thin filament along. A fresh ATP molecule binding to the head makes it let go, and splitting that ATP re-cocks the head for the next stroke, so the cycle repeats for as long as calcium and ATP are available.
Under the microscope, contraction brings neighboring Z lines nearer to each other and narrows the I band and H zone, while the width of the A band does not change. The theory also explains rigor mortis: after death, without ATP, myosin heads cannot detach.
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Where does the term “sliding filament theory” come from?
- fil-
- threadLatin filum
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Terms that go with it
- SarcomereA sarcomere is the repeating contractile unit of striated muscle, the section of a myofibril between two Z-discs where actin and myosin interact.
- Skeletal muscleSkeletal muscle is the striated, voluntary muscle tissue attached to bones by tendons that moves the body, holds posture and produces heat.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- Rigor mortisRigor mortis is the temporary stiffening of muscles after death, caused by loss of ATP, which leaves myosin locked onto actin until muscle proteins break down.
- Action potentialAn action potential is a brief, all-or-none reversal of the voltage across a nerve or muscle cell membrane that travels along the cell as a signal.
- AcetylcholineAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 10.3 Muscle Fiber Contraction and Relaxation
- OpenStax Biology 2e, 38.4 Muscle Contraction and Locomotion
- Hitchcock-DeGregori and Irving (2014), Hugh E. Huxley: The Compleat Biophysicist, Biophysical Journal
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