The Muscular muscle is a/an

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.

Correct Answer: D

Rationale: Relaxation requires multiple steps: the nerve impulse stopping halts T-tubule signals, calcium being pumped back into the sarcoplasmic reticulum (SR) removes it from troponin, shifting tropomyosin to block actin sites, and ATP binding myosin detaches it from actin, ending cross-bridges. One alone like impulse cessation won't suffice without calcium removal and detachment. Calcium pumping alone leaves myosin bound if ATP's absent. ATP detachment needs prior steps. All must occur, ensuring contraction ceases fully, distinct from partial processes, restoring the muscle to rest, integral to its cyclic function.

Correct Answer: D

Rationale: The tibialis anterior's name reflects its location anterior (front) of the tibia in the lower leg. Muscle names often denote position, here indicating its role in dorsiflexing the foot from the shin's front. Size (e.g., maximus) or shape (e.g., deltoid) apply elsewhere, not here. Fiber direction (e.g., oblique) isn't the focus location is. This positional naming distinguishes it, aligning with anatomical convention for identifying muscle placement and function.

Correct Answer: A

Rationale: The diaphragm, a dome-shaped muscle below the lungs, contracts to flatten, expanding the thoracic cavity for inspiration breathing's primary driver. External intercostals assist, lifting ribs, but diaphragm's action is dominant. Internal intercostals aid expiration, secondary to inspiration. Rectus abdominis flexes the trunk, not breathing. Diaphragm's central role in volume change sets it apart, essential for respiratory rhythm.

Correct Answer: D

Rationale: The quadriceps group rectus femoris, vastus muscles lies on the anterior thigh, extending the knee and flexing the hip, as in kicking. Abductors are lateral, adductors medial, hamstrings posterior. Quadriceps' anterior placement and extension role distinguish them, vital for leg straightening, unlike positional or opposing groups.