Abstract
Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. Currently, all researchers agree there is no single physiological role sleep serves. Nevertheless, it is quite evident that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state. This review details the physiological processes involved in sleep regulation and the possible functions that sleep may serve. This description of the brain circuitry, cell types, and molecules involved in sleep regulation is intended to further the reader’s understanding of the functions of sleep.
Highlights
Sleep occurs in every organism to some extent, indicating its physiological importance [1]
Theta rhythms are dominant during rapid eye movement sleep (REMS) [21], when recorded in the hippocampus, and occur during non-rapid eye movement sleep (NREMS), they are a minor component of the frequency spectra compared to delta rhythms
A recent study using neuronal ensemble recordings, microdialysis, and optogenetic inhibition of thalamic output to the neocortex indicated that NREMS EEG power in the 0.75–1.5 Hz frequency range occurs when T-type Ca2+ channels are active, again suggesting that Ca2+channels play a role in slow-wave activity (SWA) regulation [112]
Summary
Sleep occurs in every organism to some extent, indicating its physiological importance [1]. For the animal is less vigilant to potential predators, and sleep prohibits consumption of food and procreation. Our understanding of the basic mechanisms of sleep regulation have occurred within the past 150 years. Sleep is regulated by molecules and pathways that are redundant and serve other physiological functions, which has made our understanding of the function(s) of sleep and sleep-related pathologies arduous. We describe how sleep is regulated globally, regionally, and locally, by means of cellular and molecular mechanisms. This description may serve to suggest how these processes dictate the many functions of sleep (Figure 1)
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