Voltage-gated Na⁺ channels open upon reaching what state?

Correct Answer: B

Rationale: Voltage-gated Na⁺ channels open when the membrane potential reaches the threshold (around -55 mV), triggering an action potential. They don’t open at resting potential, during repolarization, or at overshoot.

Correct Answer: C

Rationale: The trochlear nerve (CN IV) is the smallest cranial nerve by axon count and diameter, innervating only the superior oblique muscle. The olfactory nerve (I) has many fibers, and oculomotor (III) and abducent (VI) are larger.

Correct Answer: D

Rationale: The facial nerve (CN VII) motor nucleus is in the pons, controlling facial expression muscles. The hypothalamus and midbrain are incorrect, and the third ventricle floor is unrelated.

Correct Answer: B

Rationale: The sneeze reflex’s afferent path is via the maxillary nerve (V2), sensing nasal irritation, with efferent via CN VII/X. V1 senses the cornea, V3 the jaw, and vagus (X) isn’t primary here.

Correct Answer: A

Rationale: Pancreatitis referred pain is at T7-T8, due to visceral innervation from the greater splanchnic nerve (T5-T9), projecting to the epigastric region.