Which of the following muscles is a common intra-muscular injection site?

Correct Answer: A

Rationale: The deltoid, in the upper arm's shoulder region, is a standard intramuscular injection site due to its accessible, thick muscle mass, minimizing nerve damage risk. Gluteus maximus is avoided to protect the sciatic nerve (gluteus medius is preferred), vastus medialis isn't typical, and latissimus dorsi, on the back, lacks suitable mass and access. Deltoid's prominence and safety distinguish it in clinical practice, key for effective drug delivery.

Correct Answer: D

Rationale: Skeletal muscle is striated (sarcomere-banded), voluntary (somatic control), and multinucleate (syncytial), unlike smooth (unstriated, involuntary, uninucleate) or cardiac (striated, involuntary, uninucleate) muscle. This trio defines its role in conscious movement, distinguishing it in structure and function, key to its physiological classification.

Correct Answer: B

Rationale: These muscles triceps brachii (three origins, arm), biceps femoris (two origins, thigh), quadriceps femoris (four origins, thigh) are named by origin count ('tri-,' 'bi-,' 'quad-') and location ('brachii' for arm, 'femoris' for femur). Size, shape, fibre direction, or insertions aren't specified. This origin-location convention aids anatomical identification, distinguishing them from size- or shape-based names, reflecting muscle attachment points critical for function.

Correct Answer: B

Rationale: ATP hydrolysis to ADP and phosphate energizes myosin cross-bridges, enabling them to pull actin, driving contraction. Myosin doesn't shorten, calcium binds troponin (not tropomyosin), and calcium returns to the sarcoplasmic reticulum post-contraction. This energy step distinguishes contraction's power source, essential for filament sliding, contrasting with regulatory or recovery phases.

Correct Answer: A

Rationale: Biceps femoris, a hamstring, acts on the femur and tibia, not the humerus (upper arm). Quadriceps extend the tibia, gluteals move the femur, and biceps brachii flex the radius. This mismatch distinguishes humerus-biceps femoris as non-functional, key to anatomical pairing accuracy.