What is the role of calcium in muscle contraction?
Calcium binds to tropomyosin to expose the myosin-binding sites on actin.
Calcium is released from the sarcoplasmic reticulum to initiate the sliding of actin and myosin filaments.
Calcium activates the motor neurons to stimulate muscle contraction.
Calcium is required for the relaxation of muscles after contraction.
The Correct Answer is B
Muscle contraction is a complex process that involves the interaction between actin and myosin filaments in the muscle fibers. The sliding of these filaments is initiated by the release of calcium ions from the sarcoplasmic reticulum, a specialized organelle in muscle cells. The calcium ions bind to the protein troponin, which causes a conformational change in the troponin-tropomyosin complex, exposing the myosin-binding sites on actin. This allows the myosin heads to bind to actin, forming cross-bridges that pull the actin filaments toward the center of the sarcomere, resulting in muscle contraction.
Option a) is incorrect because calcium does not bind to tropomyosin directly, but rather binds to the protein troponin, causing a conformational change in the troponin-tropomyosin complex.
Option c) is incorrect because calcium does not activate motor neurons, but rather is released from the sarcoplasmic reticulum in response to an action potential that travels down the motor neuron to the neuromuscular junction.
Option d) is incorrect because calcium is required for muscle contraction, not relaxation. The relaxation of muscles after contraction is due to the active transport of calcium ions back into the sarcoplasmic reticulum, which allows the troponin-tropomyosin complex to return to its resting conformation, blocking the myosin-binding sites on actin and ending the cross-bridge cycle.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
The scientific method is a systematic approach used to answer questions or test hypotheses about the natural world. The steps involved in the scientific method are:
- Observation: This is the first step in the scientific method. It involves observing a phenomenon or a problem and gathering information about it.
- Hypothesis: After making an observation, a scientist forms a hypothesis, which is a tentative explanation for the phenomenon or problem.
- Prediction: Based on the hypothesis, the scientist makes a prediction about what will happen in an experiment or what they will observe.
- Experimentation: The scientist designs and conducts an experiment to test the hypothesis and prediction.
- Analysis: The data collected from the experiment are analyzed to determine if they support or refute the hypothesis.
- Conclusion: Based on the analysis of the data, the scientist draws a conclusion about whether the hypothesis is supported or refuted.
Option b) is incorrect because it starts with hypothesis before observation.
Option c) is incorrect because prediction comes before experimentation.
Option d) is incorrect because hypothesis comes after observation and data collection.
Correct Answer is A
Explanation
The diaphragm is a dome-shaped muscle that plays a key role in breathing. It separates the thoracic cavity, which contains the heart and lungs, from the abdominal cavity. When the diaphragm contracts, it moves downward and increases the volume of the thoracic cavity, allowing air to flow into the lungs. When it relaxes, it moves upward and decreases the volume of the thoracic cavity, forcing air out of the lungs.
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