During inhalation, muscles contract to elevate the ribs. During forced exhalation, muscles contract to depress the ribs.

Correct Answer: A

Rationale: During inhalation, external intercostals contract to elevate the ribs, expanding the thoracic cavity for air intake, while the diaphragm also flattens. In forced exhalation, internal intercostals contract to depress the ribs, reducing cavity volume to expel air, often with abdominal muscle aid. Transverse abdominis assists exhalation but doesn't directly depress ribs. The diaphragm drives inhalation, not rib depression. Reversing intercostals is incorrect, as their roles are distinct. External intercostals for inhalation and internal for forced exhalation is the correct answer, reflecting their specific actions in respiratory mechanics, key to understanding breathing dynamics.

Correct Answer: B

Rationale: Muscles are specialized tissues responsible for movement and are classified based on structure and function. The three distinct types are cardiac, smooth, and skeletal. Cardiac muscle powers the heart, contracting involuntarily to pump blood. Smooth muscle lines organs like the stomach and blood vessels, also working involuntarily to manage processes like digestion. Skeletal muscle, attached to bones, enables voluntary movements like walking or lifting. Tendons, ligaments, and joints are connective structures, not muscle types tendons link muscle to bone, ligaments connect bones, and joints are bone junctions. Flexion and extension describe movements, not muscle categories, and stringy isn't a scientific term for muscle. The correct classification reflects the histological and functional diversity of muscle tissue, critical for understanding their roles in the body, distinguishing them from structural or movement descriptors that don't define muscle itself.

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: D

Rationale: Muscles controlling substance flow within lumens like blood vessels, digestive tract, or airways are smooth muscles. These involuntary muscles, found in organ walls, contract or relax to regulate movement, such as peristalsis in the gut or vasoconstriction in arteries, without conscious control. The hormonal system involves chemical signaling, not muscle action. The skeletal system includes voluntary muscles for locomotion, not lumen regulation. Cardiac muscles power the heart, a specific function unrelated to general lumen control. Smooth muscles' unique ability to modulate flow across diverse tubular structures makes them the best fit, as their autonomic regulation and adaptability distinguish them from striated muscles in managing internal transport.

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.