Final answer:
The 2nd stage of NREM sleep features deep relaxation, sleep spindles, and K-complexes, crucial for learning and memory.
Step-by-step explanation:
Second Stage of NREM Sleep
The second stage of NREM sleep is a period when the body enters a state of deep relaxation. This stage is primarily characterized by the presence of sleep spindles and K-complexes. Sleep spindles refer to rapid bursts of high-frequency brain waves that are important for learning and memory, while K-complexes are single, high-amplitude waves that may occur in response to environmental stimuli. Although theta waves still persist during stage 2 sleep, these sleep spindles and K-complexes are the defining features. This stage of sleep plays a crucial role in cognitive functions like memory consolidation.