The attachment of the muscle s other tendon to the movable bone is called the

Correct Answer: B

Rationale: The insertion is the tendon's attachment to a movable bone, drawn toward the origin during contraction, like the radius in the biceps brachii. The origin is the stationary end, belly is the muscle body, and aponeurosis is a tendon type. Insertion is the correct answer, as it identifies the dynamic attachment critical for movement, distinguishing it from the fixed origin in muscle mechanics.

Correct Answer: B

Rationale: During muscular contraction, the sliding filament theory explains sarcomere changes: actin filaments slide over myosin, shortening the sarcomere. The H-zone (myosin-only region) disappears as actin overlaps it. The I band (actin-only) shortens as Z lines approach each other. The A band (myosin length) remains constant, unaffected by sliding. The M line and Z lines get closer due to overall shortening. The A band widening doesn't occur, as its width is fixed by myosin filament length. The correct combination includes the H-zone vanishing, I band shortening, A band staying unchanged, and Z lines nearing the M line, reflecting the mechanics of contraction where filament overlap drives muscle shortening without altering myosin's span, a key principle in muscle physiology.

Correct Answer: C

Rationale: The A band, the dark region of a sarcomere, spans the thick myosin filaments, appearing dark under a microscope due to overlapping actin and myosin in most areas. It remains constant in length during contraction, reflecting myosin's extent. The H-zone, within the A band, is lighter, showing only myosin, narrowing as actin slides in. The Z-line anchors actin, defining sarcomere boundaries, not dark. The I band, light, contains only actin, shortening during contraction. The A band's darkness and myosin content distinguish it, central to sarcomere structure, unlike the lighter, shifting H-zone, structural Z-line, or actin-only I band, key to understanding muscle striation.

Correct Answer: D

Rationale: The latent period in a muscle twitch spans from stimulus to contraction onset, covering action potential travel, T-tubule signaling, and calcium release about 2 milliseconds. Contraction is the active shortening phase, post-latent. Relaxation follows, as muscle returns to rest. Fatigue is a state, not a twitch phase. The latent period's pre-contraction delay is unique, ensuring calcium reaches troponin before movement, distinct from active or recovery phases, critical for timing muscle activation in physiological studies.

Correct Answer: C

Rationale: The depressor anguli oris pulls the mouth's corners down, and depressor labii inferioris lowers the bottom lip, both creating frowning or pouting expressions. Chewing involves masseter and temporalis. Cheek compression is buccinator's role. Smiling uses zygomaticus. These depressors' downward actions contrast with chewing, compression, or upward smiling, key for sad or sulky faces.