You have probably noticed that your sleep quality is easily affected by factors such as light; for instance, sunlight streaming through the window into your eyes can sometimes be enough to wake you up, which is known as a zeitgeber. Research has identified a relationship between sleep and zeitgebers.
Sleep is an essential function that is needed for survival. The body can rest and recharge during sleep, ready to work at its best the next day. Lack of sleep has been linked to poor cognitive and physical performance, increased illnesses and impaired neurobehavioural functioning.
Sleep and zeitgebers in psychology
The body has mechanisms to ensure that the period of sleeping and being awake is balanced, known as homeostasis. Homeostatic balance of the sleep-wake cycle is important as it prevents people from oversleeping or not getting enough sleep.
Various factors affect the sleep-wake cycle; these are known as endogenous pacemakers and exogenous zeitgebers of sleep.
Sleep is a famous example of a circadian rhythm, flaticon.com/premium-icon
Endogenous pacemakers and exogenous zeitgebers in psychology
Biological rhythms can vary in length, and the sleep-wake cycle is known as a circadian rhythm. Circadian rhythms are cycles of physical, mental and behavioural changes that occur once every 24 hours.
As we mentioned above, two factors affect the sleep-wake cycle:
Endogenous pacemakers are genetically determined, internal biological mechanisms that specify biological rhythms.
An example of an endogenous pacemaker is the suprachiasmatic nucleus (SCN), nerve cells that are an internal clock suggested to keep the body in the 24-hour cycle we discussed above. The SCN resides in the hypothalamus.
It can detect light and then regulate melatonin accordingly (the hormone that helps you sleep) through the pineal gland.
Exogenous zeitgebers are external factors from your surroundings that affect biological rhythms, acting as triggers or prompts to your biological rhythms.
Examples of exogenous pacemakers are the presence of light, temperature, and food.
The two work in tandem, so light, an exogenous zeitgeber, will affect the SCN, an endogenous pacemaker, to regulate your sleep-wake cycle (your biological rhythm). Let's explore that a little further.
Relationship between zeitgebers and sleep
Your endogenous pacemakers and exogenous zeitgebers work in tandem, so light, an exogenous zeitgeber, will affect the SCN, an endogenous pacemaker, to regulate your sleep-wake cycle (your biological rhythm). Let's explore that a little further.
The relationship between zeitgebers and sleep are:
Sleep and Zeitgebers: Light exposure
Light is the main exogenous zeitgeber that affects sleep. There are light-sensitive receptors in the retina (part of the eye). These receptors respond to light and send signals to the brain. For example, the signal may be to wake up. When the sun rises, there is increased light. This is the time when humans wake up and start the day.
Whereas, during and after sunset, there is decreased light. The night period is when humans usually sleep.
Another way light affects the circadian rhythm is via the release of melatonin. The pineal gland, a part of the brain, secretes melatonin. Melatonin is released when the receptors indicate low light levels within your eye (SCN).
Melatonin regulates the sleep-wake cycle. There are high levels of melatonin when you are sleeping and feeling sleepy and low levels during periods of wakefulness.
Plants also react to sunlight. When plants are exposed to increased sunlight, their leaves open to absorb more nutrients to grow healthily. When there is decreased sunlight, plants do not do this to prevent losing too much water at night.
Plants react to sunlight to maximise their ability to absorb sunlight, flaticon.com/premium-icon
Sleep and Zeitgebers: Temperature
During sleep, the body's activity decreases, reducing the work it has to put in to maintain homeostasis.
During sleep, the heart rate is slower, there is less activity in areas such as the stomach, and the body's temperature is lower.
Core body temperature changes in a 24-hour cycle, affecting the sleep-wake cycle. Before falling asleep, the body's temperature lowers. Before waking up, the body's core temperature starts to rise.
The body is preparing for increased activity during wakefulness.
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