Ivy Tech APHY 101 Muscle System Practice Test 2026 – Comprehensive All-in-One Guide for Exam Success!

The sequence hinges on how ATP power and calcium signaling coordinate the binding and release of actin and myosin. When ATP has been hydrolyzed, the myosin head sits in a high-energy conformation ready to pull. Calcium ions released during stimulation bind to troponin, shifting tropomyosin away from the actin binding sites and exposing them. A myosin head then binds to actin to form a cross-bridge. The release of Pi drives the power stroke, pulling actin inward and generating force; ADP is released as the movement completes. To detach the myosin from actin, a new ATP molecule must bind to the myosin head, causing detachment. The ATP is then hydrolyzed again to reset the myosin head to the high-energy state for the next cycle. This captures the full cycle: energized myosin, calcium-exposed binding sites, cross-bridge formation, power stroke with Pi and ADP release, detachment with ATP binding, and re-cocking for another round.