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Excitation-Contraction Coupling

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A Closer Look at Excitation-Contraction Coupling:

Motor end plate with labels for ACh receptor, myofibril, motor neuron and muscle fibers image descriptionStimulation of a muscle fiber opens Na+ channels (= acetylcholine or ACh receptors) in the synaptic sarcolemma (= motor end-plate).

An image descriptioninflux of Na+ (= positive) ions through the open channels depolarize the area, producing an end-plate potential (= EPP).

Learn more about muscle tissue and how to identify it under the microscope with these videos and interactive quizzes.

The EPP generates action potentials in the sarcolemma next to the end-plate: (See the GIF below)

  1. These initial set of action potentials starts a chain reaction, as one set of action potentials stimulates others to develop.
  2. A resulting wave of excitation propagates (= spreads) along the sarcolemma. The wave of action potentials enters the muscle fiber at the transverse (T) tubules.
  3. 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.

An animation describing the steps of excitation-contraction steps

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