Question

In striated muscle contraction, the Ca₂₊ ATPase pump

A) releases Ca₂₊ from the T tubule.
B) secretes Ca₂₊ from the axon terminal.
C) is voltage-gated.
D) decreases Ca₂₊ in the sarcoplasm.
E) increases Ca₂₊ binding to TnC.

Answer 1

In striated muscle contraction, the Ca₂⁺ ATPase pump d) decreases Ca₂⁺ in the sarcoplasm by actively pumping calcium ions back into the sarcoplasmic reticulum, thus facilitating muscle relaxation after a contraction.

Step-by-step explanation:

The question asks about the role of the Ca₂⁺ ATPase pump in striated muscle contraction. The correct answer is that the Ca₂⁺ ATPase pump is responsible for actively transporting Ca₂⁺ ions back into the sarcoplasmic reticulum (SR) to decrease Ca₂⁺ concentration in the sarcoplasm. This pump plays a critical role in muscle relaxation by removing Ca₂⁺ from the sarcoplasm which detaches it from the troponin complex, leading to a conformational change in the actin filament that prevents myosin from binding to actin, thus ending the muscle contraction.

During a muscle contraction, acetylcholine (ACh) is released from the axon terminal and binds to receptors on the sarcolemma, causing an action potential that travels down the T tubules and triggers the release of Ca₂⁺ from the SR into the sarcoplasm. This released Ca₂⁺ binds to troponin (TnC), which leads to actin-myosin cross-bridges forming and muscle fiber contraction. The ATP-dependent Ca₂⁺ ATPase pump is not involved in the release or regulation of Ca₂⁺ during contraction but rather its reuptake during relaxation.

Hence, the correct answer is Option D.