Rem Sleep And Sympathetic Nervous System Activity

Sleep is a complex and mysterious body process that is essential for the human body and brain to rest, repair, and recover. While there are two types of sleep, rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, REM sleep is considered sympathetic due to the increase in sympathetic nerve activity. During REM sleep, the brain appears more active on an electroencephalogram (EEG) compared to alertness, and almost all muscles of the body are paralysed (REM atonia). The exceptions are the respiratory muscles and extraocular muscles. Sympathetic activity predominates during this phase of sleep, resulting in an increased respiratory and heart rate.

During REM sleep, sympathetic nerve activity increases and blood pressure and heart rate return to levels similar to those during wakefulness

During REM sleep, the body experiences a unique state of physiological activity, distinct from the other stages of sleep. While the body remains relaxed, with low muscle tone, the brain and eyes become highly active. This stage is characterised by rapid eye movement, increased brain activity, irregular breathing, and an elevated heart rate.

The transition into REM sleep brings about marked physical changes. The electrical activity in the brain, for instance, resembles the patterns observed during wakefulness, with cerebral neurons firing at similar intensities. The brainstem, specifically the pontine tegmentum and locus coeruleus, is thought to be the origin of this neural activity. Electrical bursts known as "ponto-geniculo-occipital waves" (PGO waves) occur in the brainstem, causing the rapid eye movements that give this sleep stage its name.

During REM sleep, sympathetic nerve activity increases significantly. This increase in nerve activity is associated with a rise in blood pressure and heart rate, returning to levels akin to those experienced during wakefulness. The surges in blood pressure may be linked to momentary restorations of muscle tone, known as "REM twitches".

The increase in sympathetic nerve activity during REM sleep is a notable feature, contrasting the reduction in sympathetic outflow observed during non-REM sleep. This shift in autonomic nervous system activity contributes to the distinct physiological state of REM sleep, with cardiovascular and respiratory measures becoming more variable.

The changes in nerve activity, blood pressure, and heart rate during REM sleep may have important implications. The hemodynamic and sympathetic alterations could potentially trigger ischemic events in individuals with vascular disease. Additionally, the surges in blood pressure associated with REM twitches could be a result of even greater vasoconstriction of skeletal muscle.

Arousal stimuli during REM sleep are associated with surges in blood pressure and the cessation of sympathetic nerve discharge

During REM sleep, there is a temporary restoration of muscle tone called "REM twitches" or "REM atonia". These twitches are associated with a cessation of sympathetic nerve discharge and a surge in blood pressure. This relationship was observed in a study by V.K. Somers et al., who found that momentary muscle tone restoration during REM sleep was accompanied by a significant increase in blood pressure and a decrease in sympathetic nerve activity.

The sympathetic nervous system plays a crucial role in regulating blood pressure and heart rate. During REM sleep, sympathetic nerve activity increases, leading to elevated blood pressure and heart rate similar to levels during wakefulness. This activation of the sympathetic nervous system during REM sleep suggests a possible link to the triggering of cardiovascular events, such as myocardial infarction and ischemic stroke, which are more frequent during the early morning hours after awakening.

The study by Somers et al. also revealed that arousal stimuli during stage 2 sleep, a shallower stage of sleep, elicited "K complexes" on the electroencephalogram. These complexes were associated with bursts of sympathetic nerve activity and transient increases in blood pressure. This finding highlights the complex interplay between sleep stages, arousal stimuli, and sympathetic nervous system activity.

In summary, arousal stimuli during REM sleep can lead to surges in blood pressure and the cessation of sympathetic nerve discharge. This relationship is a fascinating aspect of sleep physiology and has potential implications for our understanding of cardiovascular events and sleep-related disorders.

REM sleep is associated with profound sympathetic activation in normal subjects, possibly linked to changes in muscle tone

REM sleep, or rapid-eye-movement sleep, is characterized by random rapid movement of the eyes, low muscle tone throughout the body, and vivid dreaming. It is one of four stages of sleep and is associated with increased brain activity and irregular breathing and heart rate. During REM sleep, the brain acts similarly to how it does when awake, but the body experiences a temporary loss of muscle tone. This is hypothesized to be a protective measure to prevent people from acting out their dreams and injuring themselves. However, this hypothesis has been challenged by the discovery that dreams can also occur during non-REM sleep.

REM sleep is important for several reasons. Firstly, it plays a role in dreaming, with the majority of dreams occurring during this stage. Secondly, it aids in emotional processing as the brain processes emotions during REM sleep and activates the amygdala, which is involved in emotion processing. Thirdly, it contributes to memory consolidation, with the brain processing and committing new learnings and skills to memory. Finally, REM sleep may promote brain development, as newborns spend a significant amount of their sleep time in this stage.

While REM sleep is crucial for overall health and well-being, deprivation of REM sleep has been linked to various negative consequences. Studies suggest that REM sleep deprivation can interfere with memory formation and disrupt the brain's ability to generate new cells. Additionally, it can lead to psychological disturbances such as anxiety, irritability, hallucinations, and difficulty concentrating. However, it is important to note that the few rare individuals who do not experience REM sleep do not seem to have problems with memory or learning.

The hemodynamic and sympathetic changes during REM sleep could play a part in triggering ischemic events in patients with vascular disease

The early hours of the morning after waking are associated with an increased frequency of events such as myocardial infarction and ischemic stroke. The mechanisms triggering these events are not yet clear. However, research has shown that the triggering mechanisms could be related to autonomic changes occurring during sleep, particularly during rapid-eye-movement (REM) sleep.

REM sleep is a unique sleep phase characterised by random rapid eye movement, low muscle tone, and the tendency to dream vividly. During REM sleep, the brain appears more active on an electroencephalogram (EEG) compared to alertness. The body cycles between being awake and asleep throughout the day, with certain processes only happening during sleep. During sleep, the body "powers down" and most body systems, including the brain, become less active.

REM sleep is associated with profound sympathetic activation in normal subjects, possibly linked to changes in muscle tone. During REM sleep, sympathetic nerve activity, blood pressure, and heart rate increase significantly, returning to levels similar to those during wakefulness. Arousal stimuli during REM sleep, such as momentary muscle tone restoration, are associated with surges in blood pressure and the cessation of sympathetic nerve discharge.

The hemodynamic and sympathetic changes during REM sleep could play a role in triggering ischemic events in patients with vascular disease. These changes include increased sympathetic nerve activity, blood pressure, and heart rate, which may contribute to increased platelet aggregability, plaque rupture, or coronary vasospasm.

Furthermore, the suspension of homeostasis during REM sleep leads to large fluctuations in respiration, thermoregulation, and circulation, which do not occur during other sleep or wakefulness phases. The body's inability to regulate temperature during REM sleep may also be a contributing factor, as organisms become more sensitive to temperatures outside their thermoneutral zone.

Overall, the combination of hemodynamic and sympathetic changes during REM sleep could be a potential trigger for ischemic events in patients with vascular disease.

During non-REM sleep, sympathetic nerve activity, blood pressure and heart rate are lower

During non-REM sleep, the body enters a state of physiological quiescence, with neuronal activity decreasing in many brain regions. This is characterised by a reduction in sympathetic nerve activity, blood pressure, and heart rate.

Non-REM sleep is divided into four stages, with the first being the lightest stage of sleep, and the third being the deepest. During the first stage, the body transitions from wakefulness to sleep, with a slowing in brain wave frequency. In the second stage, the brain waves slow further, with noticeable pauses between bursts of electrical activity. The third and deepest stage of non-REM sleep is when the body takes advantage of the very deep sleep stage to repair injuries and reinforce the immune system. The fourth and final stage is REM sleep, during which the body returns to a state similar to wakefulness, with rapid eye movement, irregular breathing, and elevated heart rate.

During non-REM sleep, sympathetic nerve activity, blood pressure, and heart rate decline significantly. Arousal stimuli during the second stage of non-REM sleep can elicit high-amplitude deflections on the electroencephalogram (EEG), called "K complexes", which are associated with bursts of sympathetic nerve activity and transient increases in blood pressure.

The transition from non-REM sleep to REM sleep is marked by profound increases in sympathetic nerve activity, blood pressure, and heart rate, which can reach levels similar to those during wakefulness. These increases are particularly notable during the "REM twitches", or momentary restorations of muscle tone, which are associated with surges in blood pressure and abrupt cessations of sympathetic nerve discharge.

The reduction in sympathetic nerve activity, blood pressure, and heart rate during non-REM sleep suggests a modulation of the baroreceptor reflex, with a more pronounced decrease in blood pressure compared to heart rate and sympathetic nerve activity. This dynamic may be essential for maintaining adequate cerebral and cardiac perfusion during arousal, postural changes, or confrontations.

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