Sleeping with eyes closed is a common behavior of large animals. The structure of eyeball itself is not suitable for long-term exposure to air. Light-transmitting structures such as cornea can only work better if they are kept moist. Opening eyes for a long time will lead to dry eyes, which will affect the light transmission structure and vision. Therefore, people blink many times a day. This behavior does not need the active control of the brain, but is initiated by the visual nerve under external stimulation. During the blink of an eye, the liquid in the eyes will spread under the action of the eyelids.
Because of the need to conserve energy, animals have their own activities and rest time. Rest time, mainly sleeping. The brain relaxes and goes to sleep. Without the active control of levator palpebrae superioris and orbicularis oculi muscle, the eyelid will close under the natural relaxation of muscles. Moreover, the application of vision all day will consume neurotransmitters in the visual system, affect vision and make eye muscles tired after long-term activities. Therefore, it is necessary to reduce the illumination of the visual system to restore vision.
Furthermore, human hormones have obvious circadian rhythm. Due to more activities during the day, more hormones are secreted, which promotes energy release. Nervous, higher blood pressure, faster heart rate, but all systems of the human body need to rest, but some systems are too important to stop working completely and need to enter a low-energy state for a period of time, so the level of hormones that promote energy release is reduced. If you live upside down day and night for a long time, it will lead to the disorder of hormone levels in the body.
Some of these hormones are very important, such as melatonin, which is an important substance to promote sleep in mammals. When mammals are in the dark, melatonin secretion activities are immediately strengthened; Secretion stops when turning to bright environment. If you keep your eyes open, the level of melatonin in your body will be affected, which will affect your rest. If you don't have a good rest, you won't be in the state the next day. For primitive people, it means that the efficiency of hunting and gathering food will be reduced, and the lack of food will affect the later hunting and gathering, which is related to your fate. This circadian rhythm of hormones also makes people need to close their eyes during sleep and reduce the intensity of light entering their eyes.
Closing your eyes during sleep is a natural result of relaxing the orbicularis oculi muscle during rest, on the other hand, it is the result of human evolutionary history. The activity characteristics of day walking and night lying also make living things have a relatively fixed biological clock, and rest at night. Closing your eyes can promote sleep.