A 70 year old man suddenly developed loss of consciousness and right sided upper and lower limb weakness. On clinical examination, the following is true:

Correct Answer: D

Rationale: This suggests a left hemispheric stroke (e.g., MCA), causing right-sided weakness and upper motor neuron signs: absent abdominal reflexes (D, correct), exaggerated reflexes on the right (not both, B), and possible left sensory loss (not both, C). Power isn’t lost bilaterally (A). D fits best.

Correct Answer: A

Rationale: Ependymal cells (A) in the choroid plexus filter blood to produce cerebrospinal fluid (CSF). Astrocytes (B) support neurons, oligodendrocytes (C) myelinate CNS axons, and Schwann cells (D) myelinate PNS axons. A is correct.

Correct Answer: C

Rationale: The central nervous system (CNS) consists of the brain and spinal cord. The cranial cavity houses the brain, making it the correct choice. The abdominal cavity contains digestive organs, the pelvic cavity contains reproductive and urinary organs, and the thoracic cavity contains the heart and lungs—none of which include CNS components.

Correct Answer: D

Rationale: The blood-brain barrier (BBB) restricts large or charged substances. White blood cells are large and typically cannot cross the BBB unless it’s compromised. Water, sodium ions (via channels), and glucose (via transporters) can cross more readily.

Correct Answer: A

Rationale: Depolarization occurs when sodium (Na⁺) ions enter the neuron through voltage-gated channels, making the membrane potential more positive. Potassium exits during repolarization, and chloride or phosphate don’t typically drive depolarization.