A muscle that assists the prime mover by reducing undesired action or unnecessary movement.

Correct Answer: A

Rationale: Synergists are muscles that assist the prime mover by stabilizing joints or reducing unwanted movements, enhancing the efficiency of the intended action. For example, when flexing the elbow, synergist muscles stabilize the wrist to focus the biceps' effort. Antagonist' muscles oppose the prime mover, not assist it. Intramuscular (IM) injection is a medical procedure, not a muscle type. The prime mover is the primary muscle responsible for the action, not an assistant. Synergists play a crucial supportive role in refining movement, making them the correct choice, as they align with the description of reducing unnecessary motion while complementing the prime mover's function.

Correct Answer: A

Rationale: At the wrist, forearm muscles enable flexion (bending), extension (straightening), abduction (radial deviation), and adduction (ulnar deviation). At the interphalangeal joints of fingers, only flexion and extension occur, as abduction/adduction apply to spreading fingers at metacarpophalangeal joints, not interphalangeal ones. Thus, flexion, extension, abduction, and adduction describe wrist movements but not interphalangeal finger actions, making it the correct answer. Other options omit key wrist motions or include finger-relevant terms, missing the distinction required by the question, which hinges on joint-specific movement capabilities.

Correct Answer: B

Rationale: Speaking the tongue twister requires tongue mobility, handled by palatoglossus (elevates tongue), styloglossus (retracts), genioglossus (protrudes), and hyoglossus (depresses). Masseter and temporalis move the jaw, buccinator compresses cheeks, and platysma affects the neck less critical for tongue action. Risorius and zygomaticus muscles shape smiles, not speech. Mentalis and orbicularis oris move lips, secondary here. Tongue muscles are the correct answer, as they coordinate the rapid, precise movements needed for articulating this phrase, central to speech production.

Correct Answer: C

Rationale: Tendons are dense, fibrous tissues linking muscle to bone, transmitting force to enable movement. Made of collagen, they anchor muscles like the quadriceps to bones like the tibia, facilitating actions like kicking. Bone-to-bone connections are ligaments' role, stabilizing joints. Ligaments themselves connect bones, not tendons' function. Cartilage cushions joints but doesn't attach to tendons directly tendons bypass it to reach bone. This muscle-to-bone connection defines tendons' purpose, distinct from ligaments' skeletal linking or cartilage's padding. Their strength and flexibility ensure efficient motion, critical for skeletal muscle function, highlighting their unique role in the musculoskeletal system over other structures misaligned with this mechanical linkage.

Correct Answer: B

Rationale: The muscular system is an organ system, comprising muscles skeletal, smooth, cardiac working together for movement, stability, and vital functions like circulation. It's not just large or small, as size varies, but a coordinated system of organs (muscles) with specific roles. 'Unique system' is vague, lacking anatomical precision. 'Small system' underestimates its scope, covering half the body's weight. As an organ system, it integrates with skeletal and nervous systems for locomotion, digestion, and heartbeat, distinguishing it from mere size descriptors, reflecting its organized, functional unity essential for life.