Skeletal Muscle Physiology cont Diagram the chemical and

Skeletal Muscle Physiology cont. • Diagram the chemical and mechanical steps in the cross-bridge cycle and explain the effect on the muscle fiber length. Describe the end of contraction mechanisms. Muscle excitation and energy sources. • Three roles of ATP in muscle function. • Three sources of ATP for muscle function.

Sliding myofilaments shorten sarcomeres

Excitation -contraction coupling • ACh binds to, opens nicotinic Na+/K+channels • Muscle depolarizes • Ca 2+ released from sarcoplasmic reticulum • Ca 2+ binds to troponin, cross-bridge cycling between actin & myosin begins, filaments slide

http: //www. sci. sdsu. edu/movies/actin_myosin_gif. html

Draw and label a diagram to show the following stage of the cross-bridge cycle: 1. At rest, when the muscle is not stimulated.

Skeletal Muscle Physiology cont. • Diagram the chemical and mechanical steps in the cross-bridge cycle and explain the effect on the muscle fiber length. Describe the end of contraction mechanisms. Muscle excitation and energy sources. • Three roles of ATP in muscle function. • Three sources of ATP for muscle function.

End of contraction • ACh destroyed by ACh-esterase in synapse • Muscle repolarizes • Ca 2+ returned to SR by Ca 2+ active transporter • ATP hydrolysis (+Mg) reextends myosin head • Muscle elastic elements recoil, muscle returns to resting length. Titin is the largest polypeptide known (34, 350 amino acids in length). It spans from the M to Z lines.

Draw and label a diagram to show the following stage of the cross-bridge cycle: 1. 2. At death when the muscle has depleted ATP. (rigor)

Genetic mutation turns tot into superboy 4 -year-old is first documented human case, scientists say A German boy, seen here at seven-months old, has a genetic mutation that boosts muscle growth.

Excitation-Contraction Coupling • action potentials, generated at neuromuscular junction travel around sarcolemma and through Ttubules • T-tubules signal SR to release Ca 2+ into sarcoplasm (cytosol) • Ca 2+ saturates troponin (in non-fatigued state) • troponin undergoes conformational change that lifts tropomyosin away from actin filament

E-C Coupling (cont. ) • myosin head attaches to active site on actin filament forming cross-bridge • after forming cross-bridge, myosin head moves actin-myosin complex forward and ADP and Pi are released • ATP binds with myosin head, which releases actin, and returns to original position • in resting state, myosin head contains partially hydrolyzed ATP (ADP and Pi)

E-C Coupling (cont. ) • entire cycle takes ~50 ms although myosin heads are attached for ~2 ms • a single cross-bridge shortens 10 nm • as long as action potentials continue, Ca 2+ will continue to be released • when action potentials cease, SR Ca 2+ pumps return Ca 2+ ceasing contractions • skeletal motor units follow “all or nothing” principle