Which of the following best summarizes the events of excitation-contraction coupling? choose the best answer

General
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which of the following best summarizes the events of excitation-contraction coupling? choose the best answer.

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Excitation-contraction coupling is the process that links the electrical stimulus of a muscle cell to the contraction of that muscle fiber. It involves a series of events that ultimately lead to the sliding of myofilaments and muscle contraction. Here are the options to choose from:

  1. A change in membrane potential triggers the release of calcium ions from the sarcoplasmic reticulum, which bind to troponin, causing a conformational change and exposing the binding sites on actin.

  2. The action potential travels along the T-tubule, which triggers the opening of voltage-gated calcium channels in the sarcoplasmic reticulum.

  3. Calcium ions bind to troponin, causing a conformational change and exposing the binding sites on actin.

  4. Myosin heads bind to the exposed binding sites on actin, forming cross-bridges.

To choose the best answer that summarizes the events of excitation-contraction coupling, we need to understand the correct sequence of events. Let’s analyze the options:

Option 1: A change in membrane potential triggers the release of calcium ions from the sarcoplasmic reticulum, which bind to troponin, causing a conformational change and exposing the binding sites on actin.
Option 2: The action potential travels along the T-tubule, which triggers the opening of voltage-gated calcium channels in the sarcoplasmic reticulum.
Option 3: Calcium ions bind to troponin, causing a conformational change and exposing the binding sites on actin.
Option 4: Myosin heads bind to the exposed binding sites on actin, forming cross-bridges.

The correct sequence of events in excitation-contraction coupling is as follows:

  1. A change in membrane potential triggers the release of calcium ions from the sarcoplasmic reticulum.
  2. Calcium ions bind to troponin, causing a conformational change and exposing the binding sites on actin.
  3. Myosin heads bind to the exposed binding sites on actin, forming cross-bridges.
  4. The sliding of myofilaments occurs, leading to muscle contraction.

Based on the correct sequence of events, the best answer that summarizes the events of excitation-contraction coupling would be Option 1: A change in membrane potential triggers the release of calcium ions from the sarcoplasmic reticulum, which bind to troponin, causing a conformational change and exposing the binding sites on actin.