REM sleep is called paradoxical sleep because a. our heart rate is slow and steady, while our breathing is highly irregular b. we are deeply asleep but can be awakened easily c. our nervous system is highly active, while our voluntary muscles hardly move d. it leads to highly imaginative dreams that are perceived as colorless images

C. our nervous system is highly active, while our voluntary muscles hardly move

Explanation:

REM sleep stands for Rapid Eye Movement, during this phase dreams will occur. These vivid dreams cause this high activity in the nervous system. It is called paradoxical because the muscles barely move but the brain activity is still high because of the dreams.

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