Describe the two-process model and how it explains the regulation of sleep-wakefulness. (Please use your own words.)

The two-process model of sleep regulation is a theory that explains the balance between sleep and wakefulness in humans. It was proposed by Alexander Borbely in 1982. This model suggests that our sleep-wake cycle is regulated by two independent yet interconnected processes: Process S and Process C.

Process S, also known as the homeostatic sleep process, is related to the need for sleep. It operates on the principle that the longer we stay awake, the greater our need for sleep becomes. This is because while we are awake, our bodies accumulate a sleep-inducing substance called adenosine. The higher the levels of adenosine, the sleepier we feel. When we sleep, the levels of adenosine decrease, reducing our sleep need.

Process C, also known as the circadian process, is related to the timing of sleep and wakefulness. It is controlled by our internal biological clock, located in the suprachiasmatic nucleus (SCN) of the brain. This clock operates on a roughly 24-hour cycle and is influenced by external cues like light and temperature. It regulates the release of hormones like melatonin, which makes us feel sleepy at night, and cortisol, which helps us wake up in the morning.

In a healthy sleep-wake cycle, these two processes work together to ensure we get enough sleep at the right times. For example, in the evening, as the levels of adenosine (Process S) increase and the levels of melatonin (Process C) rise, we start to feel sleepy. Conversely, in the morning, as the levels of adenosine decrease and the levels of cortisol (Process C) rise, we start to feel awake.

However, disruptions to either process can lead to sleep problems. For example, jet lag is a result of a mismatch between our internal biological clock (Process C) and the external environment. Similarly, pulling an all-nighter can lead to a high sleep need (Process S) that is not met, resulting in sleep deprivation.