Respiration in the absence of the oxygen is

Correct Answer: A

Rationale: Anaerobic respiration occurs without oxygen, breaking down glucose for energy in cells, producing lactic acid instead of carbon dioxide and water. This happens during intense exercise when oxygen demand exceeds supply, like sprinting. Aerobic respiration requires oxygen, yielding more energy efficiently in mitochondria. Mastication is chewing, unrelated to respiration. 'None of the above' dismisses the clear process. Anaerobic respiration's oxygen-free nature suits short, high-energy bursts, contrasting aerobic's sustained effort, and its lactic acid byproduct explains muscle fatigue, distinguishing it from unrelated terms or processes, aligning with cellular energy dynamics under specific conditions.

Correct Answer: A

Rationale: Muscle contraction begins with a nerve impulse triggering an action potential along the sarcolemma, which travels down T-tubules to penetrate the fiber. This precedes calcium release from the sarcoplasmic reticulum, which then binds troponin to initiate actin-myosin sliding. Calcium release follows T-tubule signaling, and sliding occurs after calcium's effect. ATP hydrolysis powers the cross-bridge cycle but happens after the signal, during contraction. T-tubule impulse transmission is the first step, ensuring rapid, uniform activation, distinct from subsequent calcium dynamics, filament movement, or energy use, foundational to the contraction sequence in muscle physiology.

Correct Answer: B

Rationale: Recruitment increases contraction strength by activating more motor units neurons and their muscle fibers as effort rises. This graded response builds force, like lifting heavier weights, without changing individual fiber contraction strength. Atrophy is muscle wasting from disuse, opposite to recruitment's effect. All-or-none applies to single fiber response, not the cumulative effect of recruitment. Fatigue follows prolonged effort, not recruitment itself. Stronger contractions via recruitment reflect motor unit summation, distinguishing it from wasting, binary responses, or exhaustion, key to muscle power modulation.

Correct Answer: B

Rationale: Masseter and temporalis are primary mastication muscles, closing the jaw for chewing. Masseter elevates the mandible, temporalis assists and retracts. Buccinator aids chewing indirectly via cheeks, not jaw movement. Orbicularis oris moves lips, unrelated. Zygomaticus smiles, not chews. These two excel in jaw power, distinct from accessory, lip, or facial roles, essential for biting and grinding.

Correct Answer: A

Rationale: The rotator cuff comprises infraspinatus, supraspinatus, teres minor, and subscapularis, stabilizing the shoulder joint and enabling rotation. 'Intraspinatus' is a typo correct is infraspinatus. Teres major and deltoid assist shoulder movement but aren't cuff muscles. These four anchor the humerus, distinct from larger or adjacent muscles, vital for shoulder integrity and motion.