What characteristic of a smooth muscle cell distinguishes it from cardiac and from skeletal muscle?

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: 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.

Correct Answer: B

Rationale: Size hierarchy: muscle (organ) contains fasciculi (fibre bundles), then muscle fibres (cells), then myofibrils (fibre-length). Sarcomeres (2 micrometres) and myofilaments are within myofibrils, myosin is molecular. Only 'muscle, fasciculus, fibre, myofibril' descends correctly, distinguishing organizational scale, key to muscle structure understanding.

Correct Answer: A

Rationale: Disuse atrophy muscle shrinkage from inactivity occurs with immobilization, reducing stimulation despite intact nerves. Denervation atrophy follows nerve loss, dystrophy is genetic degeneration, and hypertrophy is growth. Disuse atrophy's link to lack of use distinguishes it, key to rehabilitation contexts.