The three initial developmental regions of the brain are the:

Correct Answer: B

Rationale: The three primary brain vesicles during early development are the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). Telencephalon and diencephalon are subdivisions of the prosencephalon, while metencephalon and myelencephalon are subdivisions of the rhombencephalon.

Correct Answer: C

Rationale: The hypothalamus monitors osmotic concentration (thirst), blood glucose, and amino acids for homeostasis, but PCO₂ (carbon dioxide) is primarily regulated by the medulla oblongata’s respiratory centers, not the hypothalamus.

Correct Answer: A

Rationale: The pia mater is the innermost meninx, directly adhering to the brain and spinal cord. The dura mater is outermost, arachnoid is middle, and 'perineural mater' is not a standard term.

Correct Answer: B

Rationale: Serotonin influences body temperature (hypothalamus), sensory perception (modulation), and sleep (via raphe nuclei). Glycine is inhibitory, acetylcholine aids arousal, dopamine affects movement, and enkephalins reduce pain.

Correct Answer: D

Rationale: All listed are involved: substance P transmits pain signals, thalamus relays them, enkephalins modulate pain, and posterior horns (spinal cord) receive sensory input. 'None of the above' is incorrect.