What type of joint is the shoulder joint?

Correct Answer: C

Rationale: The shoulder joint (glenohumeral joint) is a ball-and-socket joint, where the humerus’s rounded head fits into the scapula’s glenoid cavity, allowing a wide range of motion (e.g., rotation, abduction). Hinge joints (e.g., elbow) allow one-plane movement, pivot joints (e.g., atlas-axis) rotate, and saddle joints (e.g., thumb) have a different articulation.

Correct Answer: C

Rationale: The axial skeleton, comprising the skull, vertebral column, and rib cage, primarily serves to protect vital organs. The skull safeguards the brain, the vertebral column shields the spinal cord, and the rib cage encases the heart and lungs. While it does provide some support and attachment for muscles, its defining role is protection, distinguishing it from the appendicular skeleton, which is more involved in locomotion. Thus, 'Protecting vital organs' is the most accurate answer.

Correct Answer: C

Rationale: The neuromuscular junction is the specialized synapse where a motor neuron communicates with a skeletal muscle fiber. The motor neuron releases acetylcholine to stimulate the muscle fiber, initiating contraction. It does not involve muscle-to-muscle, muscle-to-tendon, or bone-to-bone connections, making 'A motor neuron and a muscle fiber' the correct answer.

Correct Answer: A

Rationale: In the sarcomere, myosin heads bind to actin filaments during contraction, as per the sliding filament theory. This interaction pulls actin toward the sarcomere center, shortening it. Troponin and tropomyosin regulate access to actin’s binding sites, while collagen is not involved, making 'Actin' the correct answer.

Correct Answer: C

Rationale: Sesamoid bones, like the patella, are embedded within tendons and primarily enhance muscle leverage. The patella improves the mechanical advantage of the quadriceps muscle, increasing force during knee extension. While they offer some protection, their key role is leverage, making 'Enhancing muscle leverage' the correct answer.