_____ is attached to the Z disc.
Myosin
Actin
Troponin
Myofibrils
Tropomyosin
The Correct Answer is B
Choice A reason: Myosin is the thick filament in muscle fibers and is not directly attached to the Z disc. It anchors in the center of the sarcomere at the M line and interacts with actin during contraction.
Choice B reason: Actin is the correct answer. It forms the thin filaments in muscle fibers and is directly anchored to the Z disc. This attachment allows actin to slide past myosin during muscle contraction, shortening the sarcomere.
Choice C reason: Troponin is a regulatory protein complex that binds calcium and controls the position of tropomyosin on actin filaments. It is located along the actin filament but is not attached to the Z disc.
Choice D reason: Myofibrils are bundles of actin and myosin filaments organized into sarcomeres. While they span the length of the muscle fiber and include Z discs, they are not themselves attached to the Z disc.
Choice E reason: Tropomyosin is a regulatory protein that lies along the actin filament and blocks myosin-binding sites in a relaxed muscle. It is not anchored to the Z disc.
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Related Questions
Correct Answer is C
Explanation
Choice A reason: The sella turcica is correctly named, but it is located on the sphenoid bone, not the ethmoid. This makes the pairing incorrect.
Choice B reason: The crista galli is a projection of the ethmoid bone and serves as an attachment point for the falx cerebri, not for protecting the pituitary gland. Additionally, it is not located on the sphenoid bone.
Choice C reason: This is the correct answer. The sella turcica is a saddle-shaped depression in the sphenoid bone that houses and protects the pituitary gland. It is a central feature of the cranial floor.
Choice D reason: The occipital condyles are located on the occipital bone and articulate with the first cervical vertebra. They have no role in protecting the pituitary gland.
Choice E reason: While the crista galli is correctly paired with the ethmoid bone, it does not protect the pituitary gland. Its function is related to the attachment of meninges.
Correct Answer is D
Explanation
Choice A reason: Protraction and retraction refer to the forward and backward movement of the mandible, which occurs during certain chewing motions but is not the primary movement involved in chewing.
Choice B reason: Opposition and reposition are movements of the thumb and fingers, not the mandible. They are unrelated to chewing.
Choice C reason: Pronation is a rotational movement of the forearm, not the mandible. Elevation is correct, but pronation does not apply to jaw movement.
Choice D reason: Elevation and depression are the correct movements involved in chewing. Elevation closes the jaw (biting), and depression opens it (jaw lowering).
Choice E reason: Supination is also a forearm movement and does not apply to the mandible. Depression is correct, but supination is irrelevant here.
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