muscle contraction Flashcards
What happens when an action potential arrives at the neuromuscular junction?
Calcium ions (Ca²⁺) are released from the sarcoplasmic reticulum into the sarcoplasm.
What do calcium ions do after being released?
Calcium ions bind to troponin molecules, causing a change in their shape.
How does the binding of calcium to troponin affect tropomyosin?
Tropomyosin shifts its position, exposing the myosin-binding sites on the actin filaments.
What forms when myosin heads attach to actin?
Cross-bridges are formed between the myosin heads and actin filaments.
What happens when a myosin head binds to actin?
ADP and inorganic phosphate (Pᵢ) are released, and the myosin head changes shape, nodding forward.
What is the result of the myosin head nodding forward?
The actin filament moves over the myosin filament, causing contraction.
How does the myosin head detach from the actin?
ATP binds to the myosin head, causing it to detach from the actin filament.
What happens to ATP bound to the myosin head?
ATP is hydrolyzed by ATPase into ADP and inorganic phosphate, causing the myosin head to return to its upright position.
What enables the sliding filament cycle to continue?
The hydrolysis of ATP resets the myosin head, allowing it to bind to new sites on the actin filament.
What is the overall result of the sliding filament mechanism?
The collective bending of myosin heads pulls the actin filaments over the myosin filaments, leading to muscle contraction.
