Due to the muscle attachments, a fracture to the ischial tuberosity would affect what lower limb movement?

Correct Answer: A

Rationale: The ischial tuberosity is the origin for the hamstrings (e.g., biceps femoris) and part of the adductor magnus, which adduct the thigh (move it toward the midline). A fracture disrupts these attachments, impairing adduction. Dorsiflexion (tibialis anterior) and leg extension (quadriceps) involve distal muscles unaffected by this site. Thigh flexion (iliopsoas) isn't primarily tied to the ischium. Adduction of the thigh is the correct answer, as the ischial tuberosity's role in anchoring adductors directly impacts this movement, evident in pelvic biomechanics.

Correct Answer: A

Rationale: A stretch reflex occurs when a muscle is passively stretched, triggering a rapid contraction to resist the stretch, mediated by muscle spindles and a monosynaptic reflex arc. The classic example is the knee-jerk response, where tapping the patellar tendon stretches the quadriceps, causing an immediate kick. This reflex tests spinal nerve function and is widely recognized in clinical settings. A tendon reflex, while related to tension, typically involves Golgi tendon organs inhibiting contraction, not initiating it. A flexor reflex is a polysynaptic withdrawal response to pain, not passive stretch. An ipsilateral reflex occurs on the same side but isn't specific to stretch. The knee-jerk response perfectly exemplifies a stretch reflex due to its simplicity and direct muscle activation, making it the best fit, as it's a foundational concept in neurophysiology for assessing reflex integrity.

Correct Answer: B

Rationale: In a sarcomere, the contractile unit of muscle, thick filaments are composed of myosin, a protein with cross-bridges that pull actin during contraction. This forms the dark A band, driving the sliding filament mechanism. Actin forms thin filaments, interacting with myosin, not constituting thick ones. Myoglobin stores oxygen, unrelated to filament structure. Tropomyosin regulates actin's active sites on thin filaments, not part of thick filaments. Myosin's structural and functional role in thick filaments is key, enabling force generation, distinct from actin's thin filament role, myoglobin's metabolic support, or tropomyosin's regulatory function, fundamental to muscle contraction mechanics.

Correct Answer: B

Rationale: Post-exercise deep breathing repays oxygen debt the oxygen deficit incurred when demand exceeds supply during intense activity. This restores oxygen to myoglobin, oxidizes lactic acid back to pyruvate, and regenerates ATP via aerobic respiration. Fatigue is a symptom, not the cause of breathing. Lactic acid accumulation contributes to debt but isn't the full reason oxygen replenishes broader systems. Combining them excludes fatigue's role, missing the debt's primacy. Oxygen debt drives this response, addressing metabolic recovery, distinct from fatigue's effect or lactic acid's partial role, key to post-exercise homeostasis.

Correct Answer: B

Rationale: The frontalis, on the forehead, wrinkles the brow and raises eyebrows, creating horizontal lines, as in surprise. Buccinator compresses cheeks, aiding chewing. Orbicularis oculi closes eyes, wrinkling skin around them, not the brow. Zygomaticus lifts mouth corners for smiling. Frontalis' forehead action distinguishes it, key for facial expression above the eyes.