Figure 1010

Summary of events leading to contraction of skeletal muscle. See the text for a description of the events indicated by the numerals.

3. Voltage-gated Na+ channels open, and Na+ enters the cell.

4. General depolarization spreads over the plasma membrane of the muscle cell and continues via membranes of the T tubules.

5. Voltage sensor proteins in the plasma membrane of T tubules change their conformation.

6. At the muscle cell triads, the T tubules are in close contact with the lateral enlargements of the sarcoplasmic reticulum, where gated Ca2+-release channels are activated by conformational changes of voltage sensor proteins.

7. Ca2+ is rapidly released from the sarcoplasmic reticulum into the sarcoplasm.

8. Ca2+ binds to the TnC portion of the troponin complex.

9. The contraction cycle is initiated, and Ca21 is returned to the terminal cisternae of the sarcoplasmic reticulum.

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