Mechanism of Muscle Contraction
Start with the big picture
In skeletal muscle, actin and myosin slide past one another, increasing their overlap and shortening the sarcomere without changing either filament’s length. A motor-neuron signal leads to acetylcholine release at the neuromuscular junction, membrane depolarization, and T-tubule activation. DHP receptors trigger ryanodine receptors to release calcium from the sarcoplasmic reticulum. Calcium binds troponin C, allowing myosin to interact with actin. Repeated cross-bridge cycles produce contraction: myosin attaches, performs a power stroke, detaches when ATP binds, and resets after ATP hydrolysis. ATP also supports calcium reuptake during relaxation. The lesson connects these steps with clinical examples involving abnormal RyR1 activity and blocked acetylcholine signaling.
What you'll learn
- Explain how filament sliding shortens the sarcomere without shortening actin or myosin.
- Trace excitation–contraction coupling from motor-neuron activity to calcium release.
- Describe calcium’s role in exposing actin’s myosin-binding sites.
- Outline the cross-bridge cycle and identify ATP’s roles in contraction and relaxation.
- Relate altered calcium release or acetylcholine signaling to muscle dysfunction.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
