Which of the following is not a kind or type of muscle?

Correct Answer: C

Rationale: Muscle types are cardiac, smooth, and skeletal, defined by structure and function. Cardiac drives the heart, smooth lines organs, and skeletal moves bones. Sesamoids are small bones embedded in tendons, like the patella, not muscles they enhance leverage, not contract. Including them as muscle misrepresents anatomy, as they're skeletal components. The three muscle types cover all contractile tissues, while sesamoids support mechanically, lacking muscle's cellular traits, making them the clear non-muscle outlier in this context.

Correct Answer: A

Rationale: Muscle fatigue sets in when ATP depletes, halting cross-bridge cycling as myosin can't detach or re-cock without energy, despite calcium presence. This follows prolonged activity outpacing ATP regeneration. The latent period, pre-contraction, involves signal delay, not fatigue. Relaxation begins as calcium returns to the SR, not ATP exhaustion. Lactic acid breakdown isn't a fatigue marker it accumulates, not depletes, during anaerobic effort. ATP shortage directly impairs contraction, distinguishing fatigue from timing phases or metabolic byproducts, reflecting energy failure's impact on muscle performance.

Correct Answer: B

Rationale: The flexor carpi ulnaris flexes the wrist on the ulnar (medial) side, bending it toward the forearm's little-finger edge. 'Flexor' indicates bending, 'carpi' targets the wrist, and 'ulnaris' specifies the ulna's side. Flexing or extending the ulna itself misinterprets bones don't flex, joints do. Extending the wrist contradicts 'flexor.' Its action aligns with wrist movement, distinct from bone or opposite motions, key for hand positioning.

Correct Answer: B

Rationale: Deltoid abducts the arm horizontally, lifting it sideways from the body, due to its lateral fibers' orientation. Biceps brachii flexes the elbow. Trapezius elevates or adducts scapula. Triceps brachii extends the elbow. Deltoid's abduction role, centered at the shoulder, sets it apart, vital for arm positioning, distinct from elbow or scapular functions.

Correct Answer: C

Rationale: Quadriceps extend the knee, straightening the leg, while hamstrings flex it, bending it, acting as antagonists at the knee joint. Abduction-adduction involves lateral-medial thigh motion, not their primary knee focus. Extension-flexion defines their opposing actions, distinct from side movements, crucial for leg dynamics.