Patients confined to bed and those with plaster casts immobilising a bone fracture suffer muscle wasting. What is the term used for this condition?

Correct Answer: A

Rationale: Disuse atrophy muscle shrinkage from inactivity occurs with immobilization, reducing stimulation despite intact nerves. Denervation atrophy follows nerve loss, dystrophy is genetic degeneration, and hypertrophy is growth. Disuse atrophy's link to lack of use distinguishes it, key to rehabilitation contexts.

Correct Answer: A

Rationale: A synergist assists an agonist (prime mover) by contracting to support or enhance its action, reducing unwanted movement or adding force, like the brachioradialis aiding the biceps brachii in elbow flexion. A fixator stabilizes a bone or joint (e.g., shoulder girdle muscles during arm movement), not directly helping the agonist's motion. An insertion is the muscle's movable attachment point, not a helper type. An antagonist opposes the agonist (e.g., triceps brachii vs. biceps), hindering, not aiding. Synergists' cooperative role in muscle mechanics, refining agonist efficiency, makes 'a' the correct choice.

Correct Answer: C

Rationale: The sternocleidomastoid (SCM) is a prime mover in head flexion, contracting bilaterally to bend the neck forward, originating from the sternum/clavicle and inserting on the mastoid process. Occipitofrontalis raises eyebrows and wrinkles the forehead, not flexing the head. Corrugator supercilii furrows brows, a facial expression muscle. Masseter elevates the mandible for chewing, not head flexion. SCM's powerful, direct action on cervical flexion, a key neck movement, makes 'c' the correct prime mover.

Correct Answer: A

Rationale: The pectoral girdle (shoulder girdle) is stabilized by axial muscles (e.g., trapezius, connecting spine to scapula) and scapular muscles (e.g., rhomboids, serratus anterior, anchoring scapula), balancing mobility and stability. Axial alone omits scapular contribution. Appendicular includes limb muscles, not all girdle stabilizers. Axial and appendicular overgeneralizes, as not all appendicular muscles stabilize the girdle. 'Axial and scapular' precisely identifies the stabilizing groups, making it correct.

Correct Answer: B

Rationale: The crista galli, a midline bony crest, is on the ethmoid bone's perpendicular plate, projecting upward in the cranial cavity to anchor the falx cerebri, a dural fold. The maxilla forms the upper jaw, lacking this feature. The frontal bone has the forehead and sinuses, not the crista galli. The mandible , the lower jaw, is unrelated. The ethmoid's central skull position and its role in supporting brain membranes via the crista galli, often seen in sagittal sections, make 'b' the correct bone.