Which of the following describes skeletal muscle?

Correct Answer: A

Rationale: Skeletal muscle is striated (sarcomere-banded), voluntary (somatic control), multinucleate (syncytial), and named (e.g., biceps) unlike cardiac (striated, branched, involuntary, uninucleate) or smooth (non-striated, involuntary, uninucleate) muscle. This unique profile supports conscious movement, distinguishing it in structure and function, critical for anatomical classification.

Correct Answer: A

Rationale: Acetylcholine crosses the neuromuscular junction, binding sarcolemma receptors to trigger contraction in skeletal muscle. Adrenalin and noradrenalin modulate autonomic responses, calcium acts intracellularly. Acetylcholine's somatic role distinguishes it, essential for voluntary muscle activation, contrasting with hormonal or regulatory signals.

Correct Answer: D

Rationale: Muscles of facial expression, like the orbicularis oculi or buccinator, are unique because they insert into the skin or other soft tissues of the face, allowing fine movements for expressions like smiling or frowning, unlike most skeletal muscles that attach to bones. They don't all originate from the scalp (e.g., orbicularis oris originates from facial tissues), ruling out option a. Cartilage insertions aren't typical facial cartilage is limited (e.g., nose, ears), and these muscles target skin or mucosa. Option c is false; they don't exclusively insert onto bones (e.g., zygomaticus inserts into mouth corners' skin). Insertion into the skin enables their role in facial mobility, a distinctive feature in anatomy, making it the correct answer.

Correct Answer: D

Rationale: An abductor moves a limb away from the body's midline, as in leg abduction (e.g., gluteus medius), matching option d. Flexor bends joints, decreasing angles (e.g., hamstrings). Adductor pulls toward the midline (e.g., adductor magnus). Extensor straightens joints (e.g., quadriceps). Abductor's role in lateral movement, per muscle naming conventions and kinesiology, makes 'd' the term for this action.

Correct Answer: B

Rationale: Wrist flexors (e.g., flexor carpi radialis, ulnaris) originate from the medial epicondyle of the humerus, a bony prominence anchoring forearm flexors, allowing wrist flexion. The lateral epicondyle anchors extensors (e.g., extensor carpi radialis). Carpal bones are distal, not origins. Deltoid tuberosity relates to deltoid, not wrist muscles. The medial epicondyle's role as a common flexor origin, per upper limb anatomy, makes 'b' correct.