The joint between the radius and ulna is a joint:
hinge
pivot
plane or gliding
saddle
ball-and-socket
The Correct Answer is B
Choice A reason: Hinge joints allow movement in one plane, such as flexion and extension. Examples include the elbow and knee, but the joint between the radius and ulna does not function this way.
Choice B reason: This is correct. The proximal radioulnar joint is a pivot joint, allowing rotational movement such as pronation and supination of the forearm. The radius rotates around the ulna, enabling the palm to turn up or down.
Choice C reason: Plane or gliding joints allow sliding movements between flat surfaces, such as those between carpal bones. This does not apply to the radius and ulna.
Choice D reason: Saddle joints allow movement in two planes and are found in the thumb (carpometacarpal joint). The radius and ulna do not form a saddle joint.
Choice E reason: Ball-and-socket joints allow movement in multiple directions and are found in the shoulder and hip. The radius and ulna do not form this type of joint.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A reason: Parathyroid hormone (PTH) is secreted by the parathyroid glands in response to low blood calcium levels. It stimulates osteoclast activity, leading to bone resorption and the release of calcium into the bloodstream. PTH also enhances calcium reabsorption in the kidneys and activates vitamin D to increase intestinal calcium absorption.
Choice B reason: Thyroxine, produced by the thyroid gland, primarily regulates metabolism. While it influences bone growth and development indirectly, it does not directly stimulate osteoclast activity or calcium release.
Choice C reason: Osteocalcin is a non-collagenous protein secreted by osteoblasts and is involved in bone mineralization and calcium ion homeostasis. However, it does not stimulate osteoclast activity or increase blood calcium levels.
Choice D reason: Calcitonin is secreted by the parafollicular cells of the thyroid gland in response to high blood calcium levels. It inhibits osteoclast activity, thereby reducing bone resorption and lowering blood calcium levels. It acts in opposition to PTH.
Correct Answer is A
Explanation
Choice A reason: The sarcomere is the smallest contractile unit of a skeletal muscle. It is composed of actin and myosin filaments arranged in a precise pattern that allows for muscle contraction. Sarcomeres are repeated along the length of a myofibril and are responsible for the striated appearance of skeletal muscle.
Choice B reason: The sarcoplasmic reticulum is a specialized form of endoplasmic reticulum in muscle cells that stores and releases calcium ions, which are essential for muscle contraction. However, it is not the contractile unit itself.
Choice C reason: The sarcolemma is the plasma membrane of a muscle fiber. It plays a role in conducting electrical signals but is not the structural unit responsible for contraction.
Choice D reason: A myofibril is a long, cylindrical organelle found within muscle cells that contains many sarcomeres. While it contributes to muscle contraction, it is composed of multiple sarcomeres and is not the fundamental unit.
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