Functions and Mechanisms of Sleep

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.

Keywords: EEG; cognition; energy; function; glia; immunity; mechanism; neurons; sleep.

Figure 1. Schematic of sleep regulation

Energy-related molecules as well as pathogens through their respective pathogen recognition receptors, are enhanced by waking activity, in turn signaling sleep-regulatory molecules and resultantly promoting sleep. The sleep regulatory molecules act on their respective receptors to signal neurotransmitters. The neurotransmitters alter ion channels, inducing changes in EPSPs and IPSPs and altering sleep and cortical EEG activity.

Figure 2

Electroencephalogram (EEG) and electromyogram (EMG) during non-rapid eye movement sleep (NREMS), rapid eye movement sleep(REMS), and waking sleep states in a mouse.

Figure 3

Sleep and wakefulness are determined by a balance of sleep-promoting and wake-promoting substances.