Sliding Filament Theory

Topics: Myosin, Adenosine triphosphate, Muscle contraction Pages: 2 (276 words) Published: December 18, 2012
Sliding Filament Theory

Myosin Crossbridges (small bridges on the thick filaments that extend to the thin filaments):

-Attach, rotate, detach, and reattach in rapid succession
-Results in the sliding or overlap of the actin and myosin filaments -Causes sarcomeres to contract (muscle contraction)
-Known as the sliding filament theory

Role of Adenosine Triphosphate

The sliding filament theory at the molecular level:
Nerve impulse transmitted through the muscle fiber and releases calcium ions
Calcium(in presence of troponin and tropomyosin) facilitates the interaction of myosin and actin molecules

Adenosine triphostphate (ATP) is the energy source behind the release of calcium
ATP detaches myosin from the actin molecule
ATP must be replaced through food metabolism for process to continue

Sliding filament theory overview
Physiology of muscle contraction

At rest:
1.Calcium ions are within the sarcoplasmic reticulum
2.ATP bound to thick filaments
3.Thin filaments are intact

To Begin the Process

1.The message sent by the brain
2. CNS
3. PNS
4.Neuromuscular Junction (motor unit)
5. ACH released
6.Action potential generated, altering sarcolemma
7. Calcium ions released into sarcoplasm

Calcium binds to troponin
Binding sites are exposed
Crossbridges from myosin bind to new sites
ATP breaks down into energy as heat and moves crossbridges

Contraction cont..

-Movement of crossbridge
-Thin filaments are drawn to the center of sarcomere
-Repeating cycle of crossbridge, attach, rotate, detach, and reattach in rapid succession. -Z lines are drawn together
-Sarcomere shortens

Back to resting state (muscle contraction is stopped)

-ACH stops being released, remaining is inactivated
-Calcium ions go back to sarcoplasmic reticulum by active transport -Thick and thin filaments no longer bind together
-Crossbridges break away
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