Question

Which is the first step in the contraction phase of the excitation–contraction coupling?

Answer 1

The first step in the contraction phase of the excitation–contraction coupling is Ca2+ binds to troponin.

Excitation-contraction coupling, or ECC, is the process by which an electrical signal in a muscle cell causes that muscle cell to mechanically shorten. As suggested by its name, ECC consists of two linked phases: the excitation phase and contraction phase.

First, an action potential occurs at the muscle cell membrane (also called the sarcolemma). Next, calcium is released from the sarcoplasmic reticulum and floods the cell. Then, the regulatory proteins detach from actin, allowing myosin to bind and cross-bridge cycling to proceed.

ECC is vital to the movement of all muscles in the body.

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