What is the role of myosin heads in sliding filament theory?

What is Huxley's Sliding Filament Theory?

The sliding filament theory is the explanation for how muscles produce force (or, usually, shorten). It explains that the thick and thin filaments within the sarcomere slide past one another, shortening the entire length of the sarcomere. In order to slide past one another, the myosin heads will interact with the actin filaments and, using ATP, bend to pull past the actin.

What are the steps in sliding filament theory?

Before contraction:1) no nerve impulse to myoneural junction.2) Ca++ in the sarcoplasmic reticulum3) combining of actin and myosin is prevented by a tropomyosin-troponin complex that attatches to the actin.Contraction:1) an action potential (nerve impulse) travels along a neural axon to a myoneural junction (synapse)2) Acetylcholine (neurotransmitter) is released from the synaptic vesicles of the neuron.3) acetylcholine diffuses over into the sacrolemma and the t-tubules.4) Ca++mis released from the sarcoplasmic reticulum.5) the Ca++ then binds to the actin degrading the tropomyosin-troponin complex to expose myosin attatchment sights6) the heads of the myosin myofilaments attatch to the exposed attatchment sights on actin filament7) ATP binds to the heads of the myosin filaments. breakdown of the ATP to ADP+p releases energy and causes a bending of myosin heads.8) another ATP binds to the myosin head causing it to release the actin filament then attatch again with the head unbent. again the ATP breaks down and the process continues.To relax:1) nerve impulse stops2) active transport returns Ca++ to the sarcoplasmic reticulum3) ATP's are reformed (ADP+P+energy=ATP)4) Tropomyosin-troponin complex reforms causing the myosin to release the actin5) when the filaments release each other they slide back to the resting position.

What prevents actin myofilaments from sliding backward when a myosin head releases?

During contraction, there are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.

What are the two types of myofilaments?

The two filaments involved are myosin and actin. Actin: is the framework and slides over the myosin filament when the muscle is shortened. myosin: is a thick filament Also a sacromere: is made up of the actin and myosin. It is the functional unit of a muscle fibre and extends from z line to z line. A muscle contraction: is many sacromeres shortening ( actin sliding over myosin)

Where do myosin cross bridges attach during muscle contraction?

Myosin functions as an ATPase utilizing ATP to produce a molecular conformational change of part of the myosin and produces movement. Movement of the filaments over each other happens when the globular heads protruding from myosin filaments attach and interact with actin filaments to form crossbridges. The myosin heads tilt and drag along the actin filament a small distance (10-12 nm). The heads then release the actin filament and adopt their original conformation.

What is the concept used to explain the action of filaments in muscle contraction?

Actin is the thin filament and contains troposin and tropomyosin. Myosin is the thick filament and contains the myosin heads that will later hydrolyze ATP and essentially "walk" up and down the actin filament thus shortening the sarcomere. Once calcium binds to troposin, tropomyosin will be moved away from the active myosin actin binding site and ATP hydrolysis can begin.

How does troponin facilitate cross bridge formation?

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

What does the release of ADP and P from the myosin head cause?

The release of ADP and P from the myosin heads causes the myosin heads to change shape.

What is another name for Myosin heads?

globular heads

Binding of the myosin heads sequentially prevents what?

myosin crossbridge binding

What is the sliding filament model of contraction?

The sliding filament theory is the basic summary of the process of skeletal muscle contraction. Myosin moves along the filament by repeating a binding and releasing sequence that causes the thick filament to move over the thinner filament. This progresses in sequential stages. By progressing through this sequence the filaments slide and the skeletal muscles contract and release.First Stage:The first stage is when the impulse gets to the unit. The impulse travels along the axon and enters the muscle through the neuromuscular junction. This causes full two to regulate and calcium channels in the axon membrane to then open. Calcium ions come from extra cellular fluid and move into the axon terminal causing synaptic vessels to fuse with pre synaptic membranes. This causes the release of acetylcholine (a substance that works as a transmitter) within the synaptic cleft. As acetylcholine is released it defuses across the gap and attaches itself to the receptors along the sarcolemma and spreads along the muscle fiber.Second Stage:The second stage is for the impulse spreads along the sarcolemma. The action potential spreads quickly along the sarcolemma once it has been generated. This action continues to move deep inside the muscle fiber down to the T tubules and the action potential triggers the release of calcium ions from the sarcoplasmic reticulum.Third Stage:During the third stage calcium is released from the sarcoplasmic reticulum and actin sites are activated. Calcium ions once released begin binding to Troponin. Tropomyosin blocking the binding of actin is what causes the chain of events that lead to muscle contraction. As calcium ions bind to the Troponin it changes shape which removes the blocking action of Tropomyosin (thin strands of protein that are wrapped around the actin filaments). Actin active sites are then exposed and allow myosin heads to attach to the site.Fourth Stage:The fourth stage then begins in which myosin heads attach to actin and form cross bridges, ATP is also broken down during this stage. Myosin binds at this point to the exposed binding sites and through the sliding filament mechanism the muscles contract.Fifth Stage:During the fifth stage the myosin head pulls the Actin filament and ADP and inorganic Phosphate are released. ATP binding allows the myosin to detach and ATP hydrolysis occurs during this time. This recharges the myosin head and then the series starts over again.Stage Six:Cross bridges detach while new ATP molecules are attaching to the myosin head while the myosin head is in the low-energy configuration. Cross bridge detachment occurs while new ATP attaches itself to the myosin head. New ATP attaches itself to the myosin head during this process.Stage Seven:During stage seven the ATP is broken down and used as energy for the other areas including new cross bridge formation. Then the final stage (stage 8) begins and a drop in stimulus causes the calcium concentrate and this decreases the muscle relaxation.

Do the lengths of the thick and thin filament change when a muscle contracts?

No. The myosin heads extend to the thin filament ( actin ) and pull themselves along with a stroke motion. They slide past one another, but they themselves lose none of their length in doing so.