What condition causes a stroke?

Correct Answer: D

Rationale: A stroke is caused by disruption of blood to the brain (D), either ischemic (clot) or hemorrhagic (bleed). Meningitis (A) is inflammation, lumbar puncture (B) is diagnostic, and CSF infection (C) is meningitis-related. D is correct.

Correct Answer: C

Rationale: Myelin is primarily composed of lipids (e.g., cholesterol) and proteins (e.g., myelin basic protein), which form the insulating sheath around axons. Carbohydrates and nucleic acids are not major components.

Correct Answer: B

Rationale: Ligand-gated channels open when a neurotransmitter (ligand) binds to them, allowing ions to flow. Voltage-gated channels respond to depolarization, not ligand-gated ones.

Correct Answer: D

Rationale: Metabotropic receptors require effector proteins (e.g., G-proteins) to initiate intracellular signaling cascades. Ionotropic receptors are ligand-gated channels that don’t use effector proteins.

Correct Answer: B

Rationale: The superior colliculus in the midbrain coordinates visual reflexes, including light reflexes (e.g., pupillary response via pretectal nuclei). The red nucleus and substantia nigra are motor-related, and the inferior colliculus processes sound.