What are the three categories of the muscles?

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: 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.

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.