10.3b Sarcolemma, T-Tubules, & Sarcoplasmic Reticulum: Excitation-Contraction Coupling

excitation-contraction coupling

• second physiologic event of muscle contraction

• links muscle stimulation to contraction

• involves electrical signals, Ca release, & sliding of muscle filaments for contration

2a Development of an End Plate Potential at the Motor End Plate

• ACh opens special channels in the muscle

• lets sodium in quickly and potassium out slowly

• this changes the charge & starts muscle movement

2b Initiation & Propagation of an Electrical Signal Along Sarcolemma & T-Tubules

• how electrical signal spreads across the muscle cell and inside it

• EPP starts an action signal on the muscle cell surface

• then moves along T tubules

• causes calcium release for muscle contraction

action potential

• involves 2 events: depolarization & repolarization

• muscle gets signal, Na enters making it positive (depolarization)

  • K+ exits making it neg. again (repolarization)

depolarization

change in membrane potential to a more positive value

repolarization

change in membrane potential from a depolarized value back to resting value

refractory period

• period of time that includes depolarization & repolarization

• brief period where muscle cannot be restimulated

2c Release of Ca from Sarcoplasmic Reticulum

• electrical signal reaches a triad

• voltage channels are stimulated to change shape which stimulates Ca release

• Ca releases into cytosol of muscle fiber