Which statement about thick or thin myofilaments is CORRECT?

Correct Answer: B

Rationale: Thin myofilaments comprise actin (structure), tropomyosin (covers binding sites), and troponin (calcium receptor), regulating contraction. Thick myofilaments are myosin only, with heads forming cross-bridges not binding sites and lack tropomyosin/troponin. Myosin isn't in thin filaments. This composition distinguishes thin filaments' regulatory role, critical for controlled muscle action, contrasting with thick filaments' motor function.

Correct Answer: A

Rationale: Calcium ions bind troponin, shifting tropomyosin to reveal actin's binding sites, initiating contraction. Acetylcholine triggers nerve signals, phosphate and ADP relate to ATP not regulation. Calcium's specific troponin role distinguishes it, pivotal for muscle activation, contrasting with nerve or energy molecules.

Correct Answer: A

Rationale: A muscle's origin (fixed point) and insertion (movable point) dictate its action e.g., biceps brachii originates on the scapula and inserts on the radius, flexing the elbow. Force of contraction depends on fiber type and size, not just attachments. Muscle name may reflect location (e.g., temporalis) but isn't determined solely by it action or shape also factor in. Load capacity relates to cross-sectional area, not just origin/insertion. Action's dependence on attachment points' leverage and pull direction makes 'a' the correct answer.

Correct Answer: B

Rationale: The linea alba is a long, midline tendon of collagen fibers where rectus abdominis muscles meet, running from xiphoid to pubis, aiding abdominal wall integrity. It's not a muscle , nor does it connect hip to knee (c that's the iliotibial tract). Tendinous inscriptions are transverse bands within rectus abdominis, not the linea alba. Its tendinous, central role in uniting abdominal muscles makes 'b' the correct definition.

Correct Answer: D

Rationale: A fossa is a depression or indentation in a bone, such as the mandibular fossa of the temporal bone where the mandible articulates, serving as a surface for muscle attachment or joint articulation. An air-filled cavity describes sinuses (e.g., frontal sinus), not all fossae. A hollow passage suggests a canal or foramen (e.g., carotid canal), not a fossa's shallow nature. Fused cartilage refers to structures like synchondroses, unrelated to fossae. The term 'fossa' (Latin for ditch) denotes a sunken area, making 'd' the precise anatomical definition.