Microscopically, muscle fibres contain parallel myofibrils. What are the units joined end to end within a myofibril called?

Correct Answer: D

Rationale: Myofibrils, within muscle fibres, are chains of sarcomeres Z-line-to-Z-line units containing myofilaments (actin, myosin). Myofilaments are filament strands, motor units are neuron-fibre groups, and myosin is a protein. Sarcomeres' serial linkage enables myofibril contraction, distinguishing them as the repeating structural unit, key to muscle shortening.

Correct Answer: A

Rationale: A bipennate muscle, like rectus femoris, has fibers angling into a central tendon from both sides, resembling a feather's two-sided structure, balancing force and range. Option b describes convergent (e.g., pectoralis major), not bipennate. Option c is unipennate (e.g., extensor digitorum longus), with one-sided angling. Option d suggests opposing angles, but bipennate fibers align similarly on both sides toward the tendon, not oppositely. 'a' captures the bilateral, angled insertion, a hallmark of bipennate efficiency, making it correct.

Correct Answer: D

Rationale: The diaphragm and scalene muscles aid respiration: the diaphragm contracts to expand the thoracic cavity for inhalation, while scalenes elevate the upper ribs, assisting inspiration, especially during deep breathing. Intertransversarii and interspinales stabilize vertebrae, not respiration. Semispinalis muscles extend the neck/back, not breathing. Trapezius and rhomboids move the scapula, not lungs. The diaphragm-scalene pair's direct impact on thoracic volume makes 'd' correct.

Correct Answer: B

Rationale: The frontal bone forms the forehead, extending from the supraorbital margins above the eyes to the coronal suture at the top of the skull, creating the broad, curved surface we recognize as the forehead region. The temporal bone lies on the sides of the skull, near the temples, housing the ear structures. The occipital bone forms the back and base of the skull, not the front. The parietal bones form the top and sides of the cranium, posterior to the frontal bone. The frontal bone's anterior position and its role in shaping the forehead, often visible in skull diagrams, make 'b' the correct answer in cranial anatomy.

Correct Answer: A

Rationale: Scoliosis is an abnormal mediolateral (side-to-side) curvature of the vertebral column, forming an 'S' or 'C' shape, often idiopathic or congenital, affecting spinal alignment. Kyphosis is excessive thoracic curvature (hunchback), anteroposterior. Lordosis is exaggerated lumbar curvature (swayback), also anteroposterior. Rotation isn't a curvature type but a movement. Scoliosis's lateral deviation, diagnosable via X-ray, distinguishes it, making 'a' the correct term.