Contraction of many sarcomeres results in shortening of the overall

Correct Answer: B

Rationale: Contraction of many sarcomeres, via actin-myosin sliding, shortens the myofibril, a bundle of sarcomeres within a fiber, reducing overall muscle length. Thick filaments (myosin) don't shorten actin slides over them. Motor proteins (myosin) drive this, not shortening themselves. Sarcoplasmic reticulum releases Ca²⁺, not contracting. Myofibril shortening aggregates sarcomere action, distinguishing it, key to muscle movement.

Correct Answer: C

Rationale: Smooth muscle lacks striations banded patterns from aligned sarcomeres unlike striated skeletal (multinucleate, voluntary) and cardiac (uninucleate, involuntary, branched) muscles. Involuntary control and single nuclei are shared with cardiac muscle, and branching is cardiac-specific. Smooth muscle's non-striated, spindle-shaped cells suit its role in visceral organs, distinguishing its microscopic appearance and function from the organized contractile bands of other types, key for histological identification.

Correct Answer: B

Rationale: A fascicle, a bundle of muscle fibres (cells), is larger than a single fibre, which contains myofibrils bundles of sarcomeres. Sarcomeres, the smallest contractile units, are within myofibrils. Fascicles, wrapped in perimysium, contribute to whole-muscle structure, distinguishing them as the largest listed unit, key to muscle organization and force production.

Correct Answer: B

Rationale: Triceps brachii indicates location ( brachii, arm) and origins ( tri-, three). Sartorius is whimsical (tailor's muscle), soleus reflects shape (sandal), and trapezius shape (trapezoid). Brachii's arm-specificity marks it as location-named, distinguishing it from action or whimsical terms, aiding anatomical clarity.

Correct Answer: A

Rationale: Increasing the angle between finger and hand bones means finger extension straightening from a flexed position. Extensor digitorum, on the forearm's dorsal side, contracts to pull finger phalanges, extending them at metacarpophalangeal joints. Extensor carpi ulnaris extends the wrist, flexor digitorum profundus flexes fingers, and abductor pollicis longus moves the thumb. Extensor digitorum's specific finger-extension role distinguishes it, essential for opening the hand, contrasting with wrist or thumb actions.