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 A
Explanation
A. To allow spinal cord passage:The foramen magnum is the large opening at the skull base through which the brainstem continues as the spinal cord and major vessels and nerves pass.
B. To house the pituitary gland:The pituitary gland sits in the sella turcica of the sphenoid bone, not in the foramen magnum.
C. To anchor meninges:While meninges attach to cranial structures, anchoring of meninges is not the primary role of the foramen magnum.
D. To attach facial muscles:Facial muscles attach to facial bones and soft tissue rather than to the foramen magnum.
Correct Answer is A
Explanation
A. Meissner’s corpuscles:Meissner’s corpuscles are specialized sensory receptors located in the dermal papillae that detect light touch and pressure.
B. Hair follicles:Hair follicles anchor hair shafts and may have nerve endings for hair movement detection but are not primary touch receptors.
C. Nails:Nails protect the fingertips and enhance fine touch sensitivity but do not directly detect pressure.
D. Sebaceous glands:Sebaceous glands secrete sebum to lubricate skin and hair, not to sense touch or pressure.
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