Which of the following is considered the primary physiological cause of the tendency to sleep?

• A. Increase in dopamine levels
• B. Decrease in melatonin production
• C. Activation of the sympathetic nervous system
• D. Accumulation of adenosine in the brain

Answer: (D)

Verified step by step guidance

1. Understand that the tendency to sleep is primarily influenced by physiological processes in the brain that regulate sleep-wake cycles.
2. Recognize that adenosine is a neurotransmitter that accumulates in the brain during prolonged wakefulness and promotes sleepiness by inhibiting neural activity.
3. Note that increased dopamine levels generally promote wakefulness and alertness, so they are not the primary cause of sleep tendency.
4. Understand that melatonin production typically increases to promote sleep, so a decrease in melatonin would not cause sleepiness.
5. Realize that activation of the sympathetic nervous system is associated with arousal and alertness, not sleep, making the accumulation of adenosine the key physiological factor driving the tendency to sleep.