MCQs

The parasympathetic nervous system (via the vagus nerve) slows down the heart rate (cardiac muscle) but stimulates the smooth muscles of the gastrointestinal tract to promote digestion (peristalsis). It has no direct effect on skeletal muscle, which is controlled by the somatic nervous system.

Shivering thermogenesis is mediated by skeletal muscles. Skeletal muscle fibers are characterized by being long, cylindrical, unbranched, and multinucleated, with the nuclei located peripherally just beneath the sarcolemma.

Visceral (smooth) muscle lacks the troponin complex found in skeletal (voluntary) and cardiac muscles. Instead, calcium binds to the regulatory protein calmodulin, which then activates myosin light-chain kinase (MLCK) to phosphorylate myosin and initiate contraction.

The tissue described is cardiac muscle. The specialized dark-staining regions are intercalated discs, which contain gap junctions. These gap junctions allow ions to pass freely between cells, facilitating the rapid spread of depolarization so the heart can contract as a functional syncytium.

Smooth muscle relies heavily on the influx of extracellular calcium for contraction, whereas skeletal muscle relies almost exclusively on intracellular calcium stored in the sarcoplasmic reticulum. Cardiac muscle requires both, but smooth muscle is most immediately affected by the lack of extracellular calcium.

Correct: Cardiac muscle possesses intrinsic rhythmicity and resists fatigue, allowing continuous contraction. A: Skeletal muscle fatigues comparatively quickly. B: Smooth muscle contracts slowly and is not intrinsically rhythmic in the same manner. D: Tendons do not contract. Concept: Functional adaptation of cardiac muscle.

Correct: Skeletal muscles attach to bones and allow voluntary movement. A: Cardiac muscle functions only in the heart. B & D: Smooth (visceral) muscles control internal organs. Concept: Functional classification of muscles.

Correct: Cardiac muscle fibers branch and connect through intercalated discs. A & D: Describe skeletal muscle. C: Describes smooth muscle. Concept: Structural comparison of muscle tissues.

Correct: Smooth muscle contracts slowly and involuntarily in the walls of internal organs. A & D: Skeletal muscle is voluntary. B: Cardiac muscle is limited to the heart. Concept: Physiological role of smooth muscle.

Correct: Cardiac muscle is striated and usually has one centrally placed nucleus. A: Smooth muscle lacks striations. B: Skeletal muscle has multiple peripheral nuclei. D: Ligaments are connective tissues. Concept: Microscopic comparison of muscles.

Correct: Cardiac muscle contracts involuntarily under the control of the autonomic nervous system and pacemaker cells. A: It is living tissue. C: It contracts continuously. D: It is confined to the heart. Concept: Control of muscle contraction.

Correct: Smooth muscle in blood vessel walls controls vasoconstriction and vasodilation. A: Skeletal muscle moves bones. C: Cardiac muscle forms the heart. D: Tendons connect muscles to bones. Concept: Function of smooth muscle.

Correct: Branched fibers connected by intercalated discs are unique to cardiac muscle. A: Skeletal fibers are long and unbranched. B: Smooth muscle is spindle-shaped. D: Not muscle tissue. Concept: Histology of cardiac muscle.

Correct: Skeletal muscles are attached to bones and produce voluntary body movements. A: Cardiac muscle pumps blood. B & D: Smooth (visceral) muscles control internal organs. Concept: Voluntary muscle action.

Correct: Smooth muscle consists of spindle-shaped, non-striated, uninucleate cells found in hollow organs. A: Skeletal muscle is striated and multinucleated. B: Cardiac muscle is branched and found only in the heart. D: Tendons are connective tissue. Concept: Identification of smooth muscle.

Correct: Intercalated discs synchronize contraction, while abundant mitochondria provide continuous ATP for rhythmic activity. A: Cardiac muscle is rich in mitochondria. C: It is involuntary. D: Spindle-shaped cells are characteristic of smooth muscle. Concept: Functional adaptations of cardiac muscle.

Correct: Skeletal muscle fibers are multinucleated with peripheral nuclei and visible striations. A: Cardiac muscle has one or two central nuclei. B: Smooth muscle lacks striations. D: Epithelial tissue is not muscle. Concept: Microscopic characteristics of skeletal muscle.

Correct: Skeletal muscles attach to bones and produce voluntary body movements while maintaining posture. A: Smooth muscle controls internal organs. B: Cardiac muscle pumps blood. D: Visceral muscle refers to smooth muscle. Concept: Functional role of skeletal muscle.

Correct: Cardiac and smooth muscles function without conscious control. A: Only skeletal muscle is voluntary. C & D: These statements are incorrect. Concept: Voluntary vs. involuntary muscle control.