Contraction Physiology | Excitation-Contraction Coupling
A Closer Look at Excitation-Contraction Coupling:
Stimulation of a muscle fiber opens Na+ channels (= acetylcholine or ACh receptors) in the synaptic sarcolemma (= motor end-plate).
An influx of Na+ (= positive) ions through the open channels depolarize the area, producing an end-plate potential (= EPP).
The EPP generates action potentials in the sarcolemma next to the end-plate: (See the GIF below)
- These initial set of action potentials starts a chain reaction, as one set of action potentials stimulates others to develop.
- A resulting wave of excitation propagates (= spreads) along the sarcolemma. The wave of action potentials enters the muscle fiber at the transverse (T) tubules.
- As the action potentials travel down the T tubules, calcium channels in the nearby terminal cisternae of SR open, and Ca2+ ions diffuse into the surrounding sarcoplasm. The Ca2+ ions bind to troponin proteins embedded along the thin filaments and the contraction process begins.