Final answer:
Chemicals like serotonin and dopamine play crucial roles in the transition between nREM and REM sleep stages, with sleep spindles and K-complexes being associated with stage 2 sleep. The production of melatonin is inhibited by bright light and is critical for sleep-wake cycle regulation.
Step-by-step explanation:
The chemicals that contribute to the cycling between non-rapid eye movement (nREM) and rapid eye movement (REM) sleep stages include both serotonin and dopamine. Serotonin is known to play a role in the depth and quality of nREM sleep, while dopamine is involved in facilitating REM sleep. The transition between sleep stages involves a complex interplay of these and other neurotransmitters.
Sleep spindles and K-complexes are most commonly associated with stage 2 of the sleep cycle. Moreover, melatonin, a hormone produced in the pineal gland, is inhibited by exposure to bright light and plays a significant role in regulating sleep-wake cycles by promoting sleepiness. It is also important to note that the neurotransmitter released at the neuromuscular junction is acetylcholine, not norepinephrine or serotonin.