Role of Calcium and ATP
Start with the big picture
In skeletal muscle, an action potential travels into the T-tubules and triggers calcium release from the sarcoplasmic reticulum. Calcium binds troponin C, shifting tropomyosin so myosin can interact with actin. ATP drives the cross-bridge cycle: it enables myosin to detach, and its hydrolysis prepares the myosin head for another cycle. To end contraction, ATP-powered SERCA returns calcium to the sarcoplasmic reticulum; other transporters help remove excess calcium from the cell. ATP also supports ion pumping that helps maintain conditions for repeated excitation. Smooth muscle instead uses calcium-bound calmodulin to activate myosin light-chain kinase. The lesson connects these mechanisms with ATP depletion, impaired calcium reuptake, and sustained contracture.
What you'll learn
- Describe how excitation triggers calcium release in skeletal muscle.
- Explain how calcium regulates access to actin’s myosin-binding sites.
- Outline ATP’s roles in cross-bridge cycling and calcium removal.
- Contrast calcium regulation in skeletal and smooth muscle.
- Relate ATP depletion to impaired relaxation and contracture.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
