Excitation Contraction Coupling

Dr. Niranjan Murthy H L Asst. Prof., Dept. of Physiology Sree Siddhartha Medical College & Hospital, Tumkur

SARCOTUBULAR SYSTEM T-tubule- inward extension of sarcolemma opens to exterior contain ECF run transverse to myofibrils transmit action potential L-tubule- sarcoplasmic reticulum run parallel to myofibrils terminate in terminal cisternae stores calcium ions Triads- two terminal cisternae abutting a t-tubule

Action potential

Neuromuscular transmission

End plate potential

Muscle Action potential

Propagation of muscle AP along sarcolemma

AP reaches triad via T-tubule

Depolarisation of T-tubule

Dihydropyridine receptor acts as voltage sensor

Opening of ryanodine receptors

Ca2+ influx from Sarcoplasmic reticulum Into cytoplasm

Binding of Ca2+ to Tn C

Conformational change in troponin and tropomyosin

Exposure of binding sites on actin

Interaction of actin and myosin

contraction

Active pumping of Ca2+ back into sarcoplasmic reticulum

Tropomyosin covers binding sites of actin

relaxation