Feriante Joshua, Singh Shantanu
University of Utah
Marshall University
Neurophysiological and hormonal processes are vital for maintaining normal sleep patterns and homeostasis. A healthy sleep structure is essential for promoting and safeguarding physical and mental well-being. Sleep provides numerous benefits, including energy conservation, physical recuperation, brain plasticity enhancement, memory consolidation, emotion processing, and cognitive integration. Disrupted sleep activates the body's natural mechanisms to restore a balanced sleep cycle. Sleep involves distinct phases characterized by temporary disconnection from the external environment, reduced consciousness, muscle atonia, and changes in metabolism. Please see StatPearls' companion resource, "Physiology, REM Sleep," for more information. Sleep is categorized into 2 stages—rapid eye movement (REM) and non-REM (NREM) sleep. Under normal conditions, individuals progress through a predictable sequence of stages, starting with wakefulness, moving through various NREM stages, and eventually entering REM sleep. In adults, REM sleep accounts for 20% to 25% of total sleep time, occurring every 90 to 120 minutes and increasing in duration with each cycle. Typically, there are 4 to 5 periods of REM sleep per night. REM sleep is characterized by ocular saccadic movements, muscle atonia, and fast-wave electroencephalography (EEG) patterns that resemble the waking state and are associated with dream-like activity. NREM sleep consists of 3 stages—N1, N2, and N3—each exhibiting distinct EEG wave patterns. The REM rebound effect is a compensatory response in which an individual experiences increased REM sleep temporarily. REM sleep is characterized by vivid dreams accompanied by REMs, paralysis of skeletal muscles, and EEG patterns indicating an activated cerebral cortex. When mammals and birds experience sleep deprivation, it increases the pressure to sleep and achieve REM rebound once they do sleep. For instance, horses can stand while in non-REM sleep but must lie down to enter REM sleep safely. If they are unwilling or unable to lie down, the pressure to enter REM sleep may cause them to do so while standing, leading to a sudden loss of muscle tone and a risk of dangerous falls. Several factors can cause REM rebound and an increase in REM sleep percentage, including REM sleep deprivation, withdrawal from REM-suppressing medications (such as selective serotonin reuptake inhibitors), substance withdrawal (eg, alcohol or cocaine), depression, and CPAP titration. Experimental studies utilizing EEG and hormonal assays demonstrate that human and animal subjects experiencing sleep deprivation or significant stressors exhibit an amplified frequency and intensity of REM sleep as a compensatory mechanism. REM sleep is important in brain maturation, maintaining minimal brain activity during sleep, memory consolidation, supporting brain neurotransmitter systems, and regulating emotions. REM rebound following stress serves as an important adaptive function (see Hypnogram of Sleep Stages and Cycles).
神经生理和激素过程对于维持正常睡眠模式和体内平衡至关重要。健康的睡眠结构对于促进和保障身心健康必不可少。睡眠有诸多益处，包括节约能量、身体恢复、增强大脑可塑性、巩固记忆、处理情绪以及认知整合。睡眠中断会激活身体的自然机制以恢复平衡的睡眠周期。睡眠包括不同阶段，其特征是暂时与外部环境断开联系、意识减弱、肌肉张力缺失以及新陈代谢变化。更多信息请参阅StatPearls的配套资源《生理学，快速眼动睡眠》。睡眠分为两个阶段——快速眼动（REM）睡眠和非快速眼动（NREM）睡眠。在正常情况下，个体按可预测的阶段顺序进行，从清醒开始，经过各个NREM阶段，最终进入REM睡眠。在成年人中，REM睡眠占总睡眠时间的20%至25%，每90至120分钟出现一次，且每个周期的时长会增加。通常，每晚有4至5个REM睡眠期。REM睡眠的特征是眼球快速跳动、肌肉张力缺失以及类似于清醒状态的快波脑电图（EEG）模式，且与梦境般的活动相关。NREM睡眠由三个阶段组成——N1、N2和N3——每个阶段都呈现出独特的EEG波形。REM反弹效应是一种补偿反应，个体在此期间会暂时经历REM睡眠增加。REM睡眠的特征是伴有快速眼动的生动梦境、骨骼肌麻痹以及表明大脑皮层激活的EEG模式。当哺乳动物和鸟类经历睡眠剥夺时，这会增加它们的睡眠压力，一旦它们开始睡眠就会出现REM反弹。例如，马在非REM睡眠时可以站立，但必须躺下才能安全进入REM睡眠。如果它们不愿意或无法躺下，进入REM睡眠的压力可能会导致它们站立时进入REM睡眠，从而导致肌肉张力突然丧失，并有摔倒受伤的风险。有几个因素会导致REM反弹和REM睡眠百分比增加，包括REM睡眠剥夺、停用REM抑制药物（如选择性5-羟色胺再摄取抑制剂）、物质戒断（如酒精或可卡因）、抑郁症以及持续气道正压通气（CPAP）滴定。利用EEG和激素检测的实验研究表明，经历睡眠剥夺或重大应激源的人类和动物受试者会表现出REM睡眠频率和强度的增加，作为一种补偿机制。REM睡眠在大脑成熟、睡眠期间维持最低限度的大脑活动、巩固记忆、支持大脑神经递质系统以及调节情绪方面都很重要。应激后的REM反弹是一种重要的适应功能（见睡眠阶段和周期的睡眠图）。
