During which phase of the twitch contraction is there a triggering of the release of calcium ions into the sarcoplasm?
Latent period
Contraction phase
Relaxation phase
None of the above
The Correct Answer is A
A. Latent period: This is the brief delay between the stimulus and the start of contraction. During this time, the action potential travels down the T-tubules and triggers the release of Ca2+ from the sarcoplasmic reticulum.
B. Contraction phase: This is when the actual cross-bridge cycling and muscle shortening occur (after calcium has already been released).
C. Relaxation phase: This is when calcium is actively pumped back into the sarcoplasmic reticulum.
D. None of the above: Incorrect, as the latent period specifically accounts for these excitation-contraction coupling events.
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Related Questions
Correct Answer is D
Explanation
A. Buffering: Chemical buffers in the blood (like the bicarbonate system) provide the first line of defense against pH changes.
B. Respirations: The lungs help regulate pH by exhaling or retaining carbon dioxide (CO2), which is acidic.
C. Urine secretion: The kidneys maintain long-term balance by excreting hydrogen ions (H+) and reabsorbing bicarbonate.
D. All of the above: The body requires the integrated action of chemical buffers, the respiratory system, and the urinary system to maintain a stable pH.
Correct Answer is D
Explanation
A. a relative lack of ATP: ATP is required for the cross-bridge cycle; a deficiency prevents muscle contraction and relaxation.
B. high levels of lactate: Anaerobic respiration leads to lactic acid buildup, which lowers pH and interferes with enzyme activity and calcium binding.
C. failure of the sodium-potassium pumps: Ion imbalances caused by pump failure prevent the muscle membrane from repolarizing correctly.
D. all of the above: Muscle fatigue is a complex process caused by the combination of energy depletion, chemical buildup, and ion imbalances.
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