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Action potential triggers the release of Ca²⁺ ions from the sarcoplasmic reticulum into the myofibril.

ATP is needed to actively transport Ca²⁺ ions back into the sarcoplasmic reticulum and to release the myosin heads from actin during relaxation.

Stretch receptors in muscles provide feedback to the central nervous system to maintain muscle tone and prevent overstretching.

Acetylcholine binding to receptors on the muscle fiber's membrane causes a change in permeability, leading to depolarization and an action potential.

The myosin head pivots and pulls the actin filament towards the center of the sarcomere, known as the power stroke.

The concurrent sliding of thin filaments past thick filaments on both sides of a sarcomere results in the sarcomere shortening and muscle contraction.

ATP is hydrolyzed to ADP and Pi, which provides the energy for the myosin head to return to its original position (the cocked state).

Without Ca²⁺ ions, and the troponin-tropomyosin complex in place, the muscle fiber relaxes as myosin heads can no longer bind to actin.

Muscle fatigue results from a depletion of energy reserves, accumulation of metabolic byproducts, or failure of the nervous system to provide adequate signals.

Myosin heads attach to the now-exposed binding sites on actin, forming a cross-bridge.

The action potential rapidly propagates along the sarcolemma and down into the T-tubules.

The continuous process of cross-bridge detachment and reattachment creates the sliding filament motion, shortening the sarcomere.

The binding of calcium to troponin indirectly activates myosin ATPase, which catalyzes the hydrolysis of ATP for contraction.

The calcium-troponin interaction and the subsequent movement of tropomyosin activate the thin filament for contraction.

Different types of muscle fibers (slow-twitch and fast-twitch) contract at different speeds and have varied resistance to fatigue.

A motor neuron releases the neurotransmitter acetylcholine at the neuromuscular junction, initiating a muscle contraction.

Ca²⁺ ions bind to troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin.

Upon binding of new ATP to the myosin head, the link between the myosin head and actin is weakened and the myosin head detaches.

The coordination of sarcomeres in a muscle fiber ensures even contraction and efficient force generation.

Muscle fibers utilize ATP, creatine phosphate, and anaerobic and aerobic mechanisms as energy sources for contraction.

After intense exercise, the body incurs an oxygen debt, requiring increased oxygen intake to restore metabolic conditions.

The energy from ATP hydrolysis reactivates the myosin head, preparing it for another cycle of contraction.

The enzyme acetylcholinesterase breaks down acetylcholine in the synaptic cleft, preventing continuous stimulation of the muscle fiber.

After the power stroke, ADP and Pi are released from the myosin head.

As Ca²⁺ ions are removed from troponin, tropomyosin shifts back to cover the binding sites on actin, preventing myosin interaction.

After death, the lack of ATP prevents detachment of myosin from actin, causing muscles to become rigid, a state known as rigor mortis.

Following depolarization, the muscle fiber repolarizes to its resting membrane potential by closing the sodium channels and opening potassium channels.

The myosin head restores to its high-energy or 'cocked' state, ready to form a new cross-bridge when the cycle repeats.

In some muscle types, the myosin heads remain attached to actin for an extended time without consuming more ATP, maintaining tension.