Action Potentials and Muscle Contraction

action potential propagated along the sarcolemma

at T-tubule, AP propagated along the T-tubule membrane into the interior of the muscle cell near the ends of the sarcoplasmic reticulum

depolarization of the t-tubule membrane causes nearby voltage-gated ion channels on the sarcoplasmic reticulum to open —> increases permeability of sarcoplasmic reticulum to calcium ions

calcium ions diffuse from the sarcoplasmic reticulum to the sarcoplasm

long filaments of tropomyosin proteins lie on two sides of the actin myofilament, covering up the sites where myosin myofilament can bind to the actin myofilament

globular troponin proteins attached to tropomyosin

calcium ion binds to troponin —> changes troponin confirmation and moves the tropomyosin

when tropomyosin moves, uncovers the actin’s binding sites

• allows myosin head to bind and form cross-bridges

cross-bridges play a role in muscle contraction