What is the function of the paranasal sinuses?

Correct Answer: D

Rationale: Paranasal sinuses (frontal, maxillary, etc.) warm/humidify air , produce mucus to trap debris, and lighten the skull (not a, reducing weight). All functions apply, enhancing respiration and skull structure, making 'd' correct.

Correct Answer: C

Rationale: The midsagittal plane divides the banana (or body) into equal right and left halves lengthwise, matching the split's vertical, midline cut. Coronal splits front-back, longitudinal is vague (often sagittal), transverse cuts horizontally. Midsagittal's symmetry, per planes, makes 'c' correct.

Correct Answer: A

Rationale: The A band, a sarcomere's dark-staining region under a microscope, spans the length of thick myosin filaments, overlapping with thin actin filaments in its outer zones. This overlap causes its anisotropic property, scattering light and appearing dark, unlike the isotropic (I) band's lighter, actin-only composition. Thick filaments anchor at the M line, while thin filaments extend from Z lines, partially interdigitating within the A band during rest. This dual presence distinguishes it from the H zone (thick only) and I band (thin only). The dark appearance stems from dense protein packing, observable in electron micrographs, and remains constant in length during contraction, unlike shrinking I bands. Thin filaments alone wouldn't account for the A band's width or darkness, nor would thick filaments without actin overlap explain its full structure. Muscle physiology texts confirm this composition, critical for cross-bridge formation in contraction, making the A band's dual-filament nature a cornerstone of sarcomere function.

Correct Answer: B

Rationale: The sarcoplasmic reticulum (SR), a specialized endoplasmic reticulum in skeletal muscle, stores and releases calcium to trigger contraction. Surrounding myofibrils, it sequesters calcium via calsequestrin, maintaining low cytosolic levels (10^-7 M) at rest. Upon T-tubule-transmitted action potentials, SR terminal cisternae release calcium (rising to 10^-5 M) through ryanodine receptors, binding troponin to initiate actin-myosin interaction. The sarcolemma conducts the initial depolarization, not storage. T-tubules relay signals inward but lack storage capacity. Caveoli (likely a typo for caveolae) are membrane invaginations, irrelevant here. Myofilaments use calcium but don't store it. The SR's role, detailed in muscle physiology, is critical: its ATPase pumps reuptake calcium post-contraction, relaxing the fiber. Electron microscopy reveals its extensive network, ensuring rapid, uniform calcium spread, distinguishing it from signal-conducting or contractile structures in excitation-contraction coupling.

Correct Answer: B

Rationale: After an arthrogram, where contrast dye is injected into a joint, the priority is managing potential swelling or discomfort from the procedure. Applying ice packs reduces inflammation and numbs mild pain, addressing immediate post-procedure effects. Ambulating the patient might worsen swelling or discomfort before it's controlled. Passive range-of-motion exercises could irritate the joint further, especially without first reducing inflammation. Wrapping with an elastic bandage helps with support but doesn't directly address swelling as effectively as ice in the initial stage. Ice is the first step because it tackles the physiological response to the injection, setting the stage for subsequent interventions like compression or movement, ensuring patient comfort and recovery.