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Which structure within the muscle fiber stores calcium ions necessary for muscle contraction?

A.

T-tubule

B.

Mitochondria

C.

Myofibril

D.

Sarcoplasmic reticulum

Answer and Explanation

The Correct Answer is D

A. T-tubule: T-tubules (transverse tubules) transmit action potentials into the muscle fiber and help trigger calcium release but do not store the bulk of calcium.
B. Mitochondria: Mitochondria produce ATP required for contraction and relaxation but are not the primary reservoir for calcium used in the contraction cycle.
C. Myofibril: Myofibrils are the contractile elements composed of sarcomeres (actin and myosin) and do not serve as the calcium storage organelle.
D. Sarcoplasmic reticulum: The sarcoplasmic reticulum is a specialized endoplasmic reticulum in muscle fibers that stores and releases calcium ions to initiate and terminate contraction.


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Related Questions

Correct Answer is B

Explanation

A. Osteoblasts; osteopetrosis:Osteoblasts build bone matrix and excessive activity leads to denser bone, not osteopetrosis, which involves defective bone resorption.
B. Osteoclasts; osteoporosis:Osteoclasts break down bone tissue during remodeling; when their activity outweighs bone formation, it can result in osteoporosis due to bone loss.
C. Osteocytes; osteoporosis:Osteocytes maintain the bone matrix and act as mechanosensors but do not perform resorption that causes bone thinning.
D. Chondrocytes; osteoarthritis:Chondrocytes maintain cartilage tissue, and their degeneration contributes to osteoarthritis rather than affecting bone resorption.

Correct Answer is C

Explanation

A. Synovial:Synovial describes a freely movable joint with a joint cavity and synovial fluid, not an immovable joint.
B. Amphiarthrosis:Amphiarthrosis refers to a joint that permits slight movement, such as the pubic symphysis.
C. Synarthrosis:Synarthrosis denotes an immovable joint where bones are tightly joined, for example cranial sutures.
D. Diarthrosis:Diarthrosis is another term for freely movable joints (synovial joints) that allow a wide range of motion.

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