What is the primary role of calcium ions in muscle contraction?
To bind to troponin, allowing cross-bridge formation
To stimulate the release of acetylcholine
To provide energy for muscle contraction
To transport oxygen to muscle cells
The Correct Answer is A
A. To bind to troponin, allowing cross-bridge formation: Calcium ions bind to troponin, causing a conformational change that exposes myosin-binding sites on actin and permits cross-bridge cycling.
B. To stimulate the release of acetylcholine: Calcium influx into the presynaptic nerve terminal triggers acetylcholine release, but the primary role of calcium in muscle contraction is within the muscle fiber at troponin.
C. To provide energy for muscle contraction: Energy for contraction is supplied by ATP, not by calcium ions.
D. To transport oxygen to muscle cells: Oxygen transport is the role of hemoglobin and myoglobin, not calcium ions.
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Related Questions
Correct Answer is C
Explanation
A. Brachioradialis:The brachioradialis assists forearm flexion, especially when the forearm is in a mid-position between supination and pronation, but it is not the main flexor.
B. Triceps brachii:The triceps brachii is the primary extensor of the forearm at the elbow, producing the opposite movement to flexion.
C. Biceps brachii:The biceps brachii is a major flexor of the forearm at the elbow and also contributes to forearm supination.
D. Deltoid:The deltoid primarily acts on the shoulder joint to abduct, flex, and extend the arm but does not produce elbow flexion.
Correct Answer is A
Explanation
A. Osteoarthritis:Osteoarthritis involves progressive wear and tear of articular cartilage, resulting in joint pain, stiffness, and decreased range of motion.
B. Bursitis:Bursitis is inflammation of a bursa (fluid-filled sac) causing localized pain and swelling but does not primarily involve cartilage degeneration.
C. Rheumatoid arthritis:Rheumatoid arthritis is an autoimmune inflammatory synovitis that can secondarily damage cartilage, but its hallmark is systemic synovial inflammation rather than primary degenerative cartilage loss.
D. Gout:Gout is characterized by deposition of monosodium urate crystals in joints causing acute inflammatory episodes and tophi, not primary degenerative cartilage wear.
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