Title: 10.3 Muscle Fiber Excitation, Contraction, and Relaxation – Anatomy & Physiology
Headings: 10.3 Muscle Fiber Excitation, Contraction, and Relaxation
10.3 Muscle Fiber Excitation, Contraction, and Relaxation
Learning Objectives
The Neuromuscular Junction
External Website
Excitation-Contraction Coupling
Contraction and Relaxation
External Website
Cross-Bridge Cycling
Sources of ATP
Relaxation of a Skeletal Muscle
Muscle Strength
Interactive Link Questions
Review Questions
Critical Thinking Questions
Glossary
Solutions

Content: A cross-bridge forms between actin and the myosin heads triggering contraction. As long as Ca ++ ions remain in the sarcoplasm to bind to troponin, and as long as ATP is available, the muscle fiber will continue to shorten. Relaxation of a Muscle Fiber: Ca ++ ions are pumped back into the SR, which causes the tropomyosin to reshield the binding sites on the actin strands. A muscle may also stop contracting when it runs out of ATP and becomes fatigued. Muscle contraction usually stops when signaling from the motor neuron ends, which repolarizes the sarcolemma and T-tubules, and closes the calcium channels in the SR. Ca ++ ions are then pumped back into the SR, which causes the tropomyosin to re-cover the binding sites on actin ( Figure 10.3.2 ). External Website
The release of calcium ions initiates muscle contractions. Watch this video to learn more about the role of calcium. ( a) What are “T-tubules” and what is their role? (