The blood-brain barrier restricts passage of:

Correct Answer: B

Rationale: The blood-brain barrier (BBB), formed by tight junctions in capillaries, restricts ions like Na⁺ to protect the brain. Lipid-soluble compounds and water pass more easily, while lipids are not specifically restricted.

Correct Answer: C

Rationale: Nerves are indeed bundles of axons (A, true). Neuralgia (B) is nerve pain, not a tissue (false, but not the answer). Axons begin at the axon hillock (D, true). Motor nerves (C) are not classified into 3 types (typically just somatic and autonomic), making it the false statement.

Correct Answer: B

Rationale: Pain perception occurs in the cortex, not hypothalamic nuclei (B is incorrect as stated, but none fully fit). Pain is a protective sign (A is subjective), fast pain is carried by A-delta fibers (not C-fibers, ruling out C), and referred pain is typically visceral to somatic (not somatic to visceral, ruling out D). No fully correct option exists; B is closest if reinterpreted as cortical perception.

Correct Answer: C

Rationale: Gamma efferents adjust muscle spindle sensitivity and are influenced by higher centers (behavior, A; anxiety, B) and descending tracts (extrapyramidal, D). Scratching (C) is a motor action, not a direct controller of gamma efferents. C is the correct answer.

Correct Answer: C

Rationale: Midbrain reflexes include the hopping reaction (C) and placing reaction, adjusting limb position. Stretch reflex (A) is spinal, tonic neck reflex (B) is medullary/spinal, and positive supporting (D) is medullary. C is correct.