Final answer:
The reticular formation is related to sleep and wakefulness, while the periaqueductal gray and tectal area of the mesencephalon are not involved in pain or waking up.
Step-by-step explanation:
The reticular formation, a diffuse region of gray matter throughout the brain stem, is related to sleep and wakefulness, including general brain activity and attention.
The periaqueductal gray and the tectal area of the mesencephalon are not directly involved in pain or waking up. The periaqueductal gray is involved in pain modulation, while the tectal area of the mesencephalon is related to sensory processing and the regulation of eye movements.
Therefore, the correct option is b. Reticular nuclei.