A 75 year old man gradually presented with left sided tremor especially at rest, and poverty of movement and a festinant gait. On clinical examination of this patient the following is true:

Correct Answer: B

Rationale: This describes Parkinson’s: rest tremor, bradykinesia, festinant gait, and mask-like face (B, correct). Rigidity (not hypotonia, A), normal power (not severely affected, C), and normal reflexes (not absent, D) are typical. B is correct.

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: White matter in the brain is primarily composed of myelinated axons, which are nerve fibers coated with myelin to speed up signal transmission. Neuronal cell bodies dominate gray matter, not white matter. Ganglia and dendrites from the enteric nervous system are not primary components of brain white matter.

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.