Medulla oblongata controls consciousness and arousal (the reticular formation) and its three vital reflex centers control the blood vessels diameter, heartbeat and breathing rate (the involuntary actions). This makes option D correct. The lower part of brain stem forms the hind brain which comprises of medulla oblongata, pons and cerebellum. This makes option C incorrect as medulla is not part of forebrain. Cerebellum is the convoluted subdivision of brain stem and is associated with coordination of muscular movement, muscle tone and balance i.e. the voluntary actions. Option B is incorrect. Spinal cord, along with brain, forms central nervous system which serves to integrate the sensory inputs from internal and external environment as received by sensory neurons and process and finally transmit the nerve impulses to effectors (muscles and glands). This makes option A incorrect.
