How many types of muscles are present in the body?

Correct Answer: C

Rationale: The body has three muscle types: cardiac, smooth, and skeletal, each with distinct roles. Cardiac muscle, in the heart, pumps blood involuntarily. Smooth muscle, in organs like the intestines, manages involuntary tasks like digestion. Skeletal muscle, attached to bones, drives voluntary movements like walking. Suggesting four or five types might confuse these with subtypes (e.g., fast-twitch skeletal) or non-muscle tissues, but anatomy recognizes only three based on structure and control. Two undercounts by omitting one, missing the full scope. Three aligns with histological and functional classification, reflecting their specialized purposes cardiac for circulation, smooth for visceral action, skeletal for locomotion. This trio covers all muscular functions, providing a clear, consistent framework for understanding the body's movement and maintenance systems.

Correct Answer: D

Rationale: Myoglobin, a red pigment in muscle fibers, binds and stores oxygen, releasing it during activity when blood supply can't meet demand, like in intense exercise. This supports aerobic respiration in mitochondria, especially in slow-twitch fibers. Hemoglobin, also red, transports oxygen in blood, not storing it in muscles. Erythrocytes are red blood cells carrying hemoglobin, not pigments themselves. Sarcoplasm is the muscle cell's cytoplasm, not a pigment or oxygen store. Myoglobin's muscle-specific oxygen storage distinguishes it, enhancing endurance by buffering oxygen availability, unlike hemoglobin's circulatory role or the non-storage nature of sarcoplasm and erythrocytes, aligning with its biochemical function in muscle tissue.

Correct Answer: A

Rationale: Muscle fatigue sets in when ATP depletes, halting cross-bridge cycling as myosin can't detach or re-cock without energy, despite calcium presence. This follows prolonged activity outpacing ATP regeneration. The latent period, pre-contraction, involves signal delay, not fatigue. Relaxation begins as calcium returns to the SR, not ATP exhaustion. Lactic acid breakdown isn't a fatigue marker it accumulates, not depletes, during anaerobic effort. ATP shortage directly impairs contraction, distinguishing fatigue from timing phases or metabolic byproducts, reflecting energy failure's impact on muscle performance.

Correct Answer: B

Rationale: The flexor carpi ulnaris flexes the wrist on the ulnar (medial) side, bending it toward the forearm's little-finger edge. 'Flexor' indicates bending, 'carpi' targets the wrist, and 'ulnaris' specifies the ulna's side. Flexing or extending the ulna itself misinterprets bones don't flex, joints do. Extending the wrist contradicts 'flexor.' Its action aligns with wrist movement, distinct from bone or opposite motions, key for hand positioning.

Correct Answer: B

Rationale: Deltoid abducts the arm horizontally, lifting it sideways from the body, due to its lateral fibers' orientation. Biceps brachii flexes the elbow. Trapezius elevates or adducts scapula. Triceps brachii extends the elbow. Deltoid's abduction role, centered at the shoulder, sets it apart, vital for arm positioning, distinct from elbow or scapular functions.