The _____ is the internal clock that tells people when to wake up and when to fall asleep.

• A. amygdala
• B. hippocampus
• C. pons
• D. suprachiasmatic nucleus

Answer: (D)

Verified step by step guidance

1. Identify the function of the internal clock in the human body, which is responsible for regulating sleep-wake cycles.
2. Understand that the internal clock is part of the circadian rhythm system, which is influenced by external cues like light and darkness.
3. Recognize that the suprachiasmatic nucleus (SCN) is a small region in the brain located in the hypothalamus, which plays a crucial role in controlling circadian rhythms.
4. Differentiate the SCN from other brain structures such as the amygdala, hippocampus, and pons, which have different functions related to emotions, memory, and basic life functions, respectively.
5. Conclude that the suprachiasmatic nucleus is the correct answer as it is the primary internal clock that regulates when to wake up and when to fall asleep.