Which portion of the ventricular system is found within the diencephalon?

Correct Answer: B

Rationale: The third ventricle (B) lies within the diencephalon, between the thalami. Lateral ventricles (A) are in the telencephalon, cerebral aqueduct (C) in the midbrain, and fourth ventricle (D) between pons and cerebellum. B is correct.

Correct Answer: A

Rationale: Microglia are the resident macrophages of the CNS, acting as immune cells behind the blood-brain barrier. Astrocytes support neurons, Schwann cells myelinate PNS axons, and satellite cells support PNS cell bodies.

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: D

Rationale: Acetylcholine (ACh) is released at the neuromuscular junction to stimulate skeletal muscle contraction. Norepinephrine acts at sympathetic synapses, not the neuromuscular junction.

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.