Which fatigue more quickly, slow twitch fibers or fast twitch fibers?

Correct Answer: B

Rationale: Fast-twitch fibers fatigue quickly, relying on anaerobic glycolysis for rapid, powerful contractions, like sprinting, depleting ATP and accumulating lactic acid fast. Slow-twitch fibers, rich in mitochondria and myoglobin, use aerobic respiration for endurance, fatiguing slower, as in marathons. Equal fatigue ignores their metabolic differences. Non-fatiguing fibers don't exist both tire, but at different rates. Fast-twitch's high-energy, low-endurance profile contrasts slow-twitch's sustained capacity, distinguishing their roles in activity duration and fatigue onset.

Correct Answer: D

Rationale: Iliopsoas flexes the thigh, lifting it toward the torso, as in stepping. Gluteus maximus extends it, straightening the hip, as in standing. Abduction-adduction involves lateral shifts, not their hip-centric actions. Flexion-extension captures their opposing roles, distinct from side movements, essential for thigh positioning.

Correct Answer: A

Rationale: Myasthenia gravis, an autoimmune condition, weakens muscles by antibodies destroying acetylcholine receptors, impairing nerve-muscle signals, causing fatigue. Amyotrophic lateral sclerosis (ALS, Lou Gehrig's) is neurodegenerative, not autoimmune. Fibromyalgia is pain-focused, not receptor-based. Myasthenia's receptor-specific weakness sets it apart, treatable with immunosuppressants, distinct from nerve or pain conditions.

Correct Answer: A

Rationale: The coronal suture runs transversely across the skull, separating the frontal bone (forehead) from the two parietal bones (top sides). This suture, visible as a line in coronal section, allows cranial growth in infancy and fuses later. The sagittal suture, midline, joins the parietal bones, not the frontal. The lambdoid suture separates parietals from the occipital bone posteriorly. 'Frontal' as a suture is incorrect it's the bone itself. The coronal suture's position and function distinguish it, essential for skull structure and development, unlike sagittal or lambdoid orientations or misnamed bone references.

Correct Answer: D

Rationale: Adipose tissue is the body's largest endogenous substrate source, storing vast triglyceride reserves thousands of grams far exceeding other stores, providing energy via lipolysis during prolonged activity. Muscle glycogen, about 300-500 grams in trained individuals, fuels local contraction but is limited. Liver glycogen, around 100 grams, maintains blood glucose but depletes quickly. Intramuscular lipids, small triglyceride droplets, contribute modestly, far less than adipose's capacity. Adipose tissue's sheer volume and energy density (9 kcal/g) dwarf glycogen's stores (4 kcal/g), distinguishing it as the primary reserve, key for sustained energy needs beyond glycogen's scope.