The brain's descending pain modulatory system ________.

• A. operates only during sleep and has no effect during wakefulness
• B. functions independently of any hormonal influence from the endocrine system
• C. is solely responsible for the production of endorphins in the adrenal glands
• D. can inhibit or enhance pain signals through pathways that originate in the brain and project down to the spinal cord

Answer: (D)

Verified step by step guidance

1. Understand the role of the brain's descending pain modulatory system, which involves neural pathways that originate in the brain and project down to the spinal cord.
2. Recognize that this system can both inhibit and enhance pain signals, meaning it modulates pain perception rather than simply turning it on or off.
3. Recall that this system is active during wakefulness and is not limited to sleep, so the option stating it operates only during sleep is incorrect.
4. Consider the interaction between the nervous system and the endocrine system; the descending pain modulatory system does not function completely independently of hormonal influences, so that option is inaccurate.
5. Note that endorphins are produced primarily in the brain and nervous system, not solely in the adrenal glands, so the statement about endorphin production being solely in the adrenal glands is false.