What is the functional role of the T tubules?
Hold cross bridges in place in a resting muscle
Support the muscle fiber
Stabilize the G and F actin
Enhance spread of muscle action potential throughout muscle fiber
Synthesize glucose to provide energy for muscle contraction
The Correct Answer is D
Choice A reason: Cross bridges are formed between actin and myosin during contraction. T tubules do not hold them in place; their role is electrical, not structural.
Choice B reason: While T tubules are embedded in the muscle fiber, their function is not to provide structural support. That role is fulfilled by connective tissues like endomysium and cytoskeletal proteins.
Choice C reason: G and F actin are stabilized by proteins like tropomyosin and nebulin, not T tubules. T tubules are involved in electrical signaling.
Choice D reason: This is the correct answer. T tubules are invaginations of the sarcolemma that conduct action potentials deep into the muscle fiber. This ensures that the signal for contraction reaches all parts of the muscle simultaneously, triggering calcium release from the sarcoplasmic reticulum.
Choice E reason: Glucose synthesis occurs in the liver and other tissues via gluconeogenesis. Muscle cells use glucose for energy but do not synthesize it through T tubules.
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Related Questions
Correct Answer is E
Explanation
Choice A reason: Osteoclasts are large, multinucleated cells responsible for bone resorption. They do not arise from osteoblasts and are not involved in matrix secretion.
Choice B reason: Osteogenic cells are stem cells that differentiate into osteoblasts. They are precursors, not the result of matrix entrapment.
Choice C reason: Chondrocytes are cartilage cells, not bone cells. They originate from chondroblasts and are unrelated to osteoblast transformation.
Choice D reason: Osteoid refers to the unmineralized bone matrix secreted by osteoblasts. "Osteoid cell" is not a recognized term for a mature bone cell.
Choice E reason: Osteocyte is the correct answer. Once an osteoblast becomes encased in the bone matrix it secretes, it differentiates into an osteocyte. Osteocytes reside in lacunae and maintain bone tissue.
Correct Answer is A
Explanation
Choice A reason: ATP (adenosine triphosphate) is the primary energy currency of the cell. Muscle cells use ATP to power the contraction process, converting chemical energy into mechanical energy through the interaction of actin and myosin filaments.
Choice B reason: Kinetic energy is the result of movement, not the source of energy for muscle contraction. Muscles generate kinetic energy, but they do not transform it into mechanical energy.
Choice C reason: Potential energy refers to stored energy, such as in a stretched elastic band. While muscles can store potential energy in elastic components, the transformation into mechanical energy is driven by ATP.
Choice D reason: DNA carries genetic information and plays no direct role in energy transformation during muscle contraction.
Choice E reason: Myoglobin stores oxygen in muscle cells but does not provide energy. It supports aerobic metabolism, which ultimately produces ATP, the actual energy source.
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