Questions: QUESTION 1 The sudden rush of which ion into the sarcoplasm produces an action potential in the sarcolemma? ANSWER O Magnesium O Phosphate O Calcium O Sodium O I DON'T KNOW YET Learning Chapter 7 Sections 1-5

The answer is: Calcium

Explanation for each option:

• Magnesium: Magnesium ions do not typically produce an action potential in the sarcolemma. They play other roles in muscle function, such as stabilizing ATP and acting as a cofactor for various enzymes.

• Phosphate: Phosphate ions are not responsible for generating action potentials in the sarcolemma. They are involved in energy transfer and storage within cells.

• Calcium: Calcium ions are crucial for muscle contraction. When they rush into the sarcoplasm, they bind to troponin, which leads to the exposure of binding sites on actin filaments, allowing for muscle contraction. However, the initial action potential in the sarcolemma is primarily due to sodium ions, not calcium.

• Sodium: Sodium ions are primarily responsible for generating action potentials in the sarcolemma. The influx of sodium ions into the muscle cell depolarizes the membrane, leading to an action potential.

• I DON'T KNOW YET: This option indicates uncertainty and is not a correct answer.

Summary: While calcium ions play a critical role in muscle contraction, the initial action potential in the sarcolemma is primarily due to the influx of sodium ions.