What structure in skeletal muscle cells functions in calcium storage?
Myofibrillar network
Sarcoplasmic reticulum
T tubules
Mitochondria
Intermediate filament network
The Correct Answer is B
Choice A reason: The myofibrillar network refers to the arrangement of actin and myosin filaments responsible for muscle contraction. While essential for force generation, it does not store calcium. Its role is mechanical, not regulatory in terms of calcium ion concentration.
Choice B reason: The sarcoplasmic reticulum is a specialized form of smooth endoplasmic reticulum found in muscle cells. It functions as the primary site for calcium storage and release during muscle contraction. Upon stimulation, it releases calcium ions into the cytosol, initiating the interaction between actin and myosin filaments. This makes it the central regulator of calcium dynamics in skeletal muscle.
Choice C reason: T tubules (transverse tubules) are invaginations of the sarcolemma that help propagate action potentials into the interior of the muscle fiber. They facilitate communication between the sarcolemma and the sarcoplasmic reticulum but do not store calcium themselves.
Choice D reason: Mitochondria are responsible for ATP production through oxidative phosphorylation. Although they can buffer calcium to some extent, they are not the primary calcium storage organelle in skeletal muscle cells.
Choice E reason: The intermediate filament network provides structural support and maintains the integrity of the cell’s shape. It does not have a role in calcium storage or release during muscle contraction.
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Related Questions
Correct Answer is C
Explanation
Choice A reason: Tendons attach muscles to bones, not to articular cartilage. Cartilage does not serve as an attachment site for tendons.
Choice B reason: Red blood cells are produced in the red bone marrow, which is found in spongy bone, not in articular cartilage.
Choice C reason: Articular cartilage is composed of hyaline cartilage and covers the ends of bones in synovial joints. It provides a smooth, lubricated surface for articulation and acts as a cushion to absorb compressive forces during movement.
Choice D reason: Bone length increases through growth at the epiphyseal plate, not through articular cartilage.
Choice E reason: The synovial membrane lines the joint capsule and produces synovial fluid. It is a separate structure from articular cartilage.
Correct Answer is A
Explanation
Choice A reason: The talus is a tarsal bone in the ankle that articulates with the tibia and fibula. It is not embedded within a tendon and therefore not classified as a sesamoid bone.
Choice B reason: The radius is one of the two long bones in the forearm. It is not a sesamoid bone, as it is not formed within a tendon.
Choice C reason: The femur is the longest and strongest bone in the body, located in the thigh. It is a long bone, not a sesamoid bone.
Choice D reason: The hamate is a carpal bone in the wrist. It is not embedded in a tendon and thus not a sesamoid bone.
Choice E reason: The patella, or kneecap, is the most well-known example of a sesamoid bone. It is embedded within the quadriceps tendon and functions to protect the knee joint and improve leverage during leg extension.
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