![]() ![]() This retinal input makes is well-suited for its role as the major circadian clock in the human brain. It receives input from the retina regarding light intensity. The suprachiasmatic nucleus (SCN) is situated directly above the optic chiasm. The activity of RAS and hence the sleep-wake cycle is heavily regulated by nuclei present within the hypothalamus. The tuberomammillary nucleus contains histaminergic neurones and also plays an essential role in wakefulness and arousal but also memory. Their activation is responsible for the shift from slow waves of sleep rhythms to higher-frequency awake rhythms. ![]() This complex is located within the pons and the midbrain and contains cholinergic neurones that project to areas including the thalamus and cortex. The pedunculopontine and laterodorsal tegmental nuclei are collectively referred to as the pontomesencephalotegmental complex. Hence, it has a direct role in circadian rhythm regulation together with arousal and attention. It directly communicates with the hypothalamic suprachiasmatic nucleus. The raphe nuclei contain serotonin-containing cells. However, it is primarily involved in increasing the brain’s excitability upon wakefulness and arousal. The activity of this nucleus can affect REM sleep. It is activated by hypocretin (orexin) from the lateral hypothalamus. The nucleus coeruleus contains noradrenergic neurones, which project to the cortices of the cerebrum and cerebellum. The RAS is composed of four main components, all of which play key roles in wakefulness and arousal. It plays a critical role in regulating cortical alertness, wakefulness, and attention. The reticular activating system (RAS), located in the anterior brainstem, is the central neurological regulatory centre for the sleep-wake cycle. Neurological regulation of sleep and wakefulness is distributed between two major anatomical structures the brainstem, harbouring the ret icular activating system (RAS) , and the hypothalamus, harbouring the suprachiasmatic nucleus (SCN). The sleep-wake cycle is under a series of complex neurological and endocrine influences. Stages 3 and 4 may disappear altogether in later cycles. This cycle repeats throughout the night.Īs the night progresses, the proportion of REM sleep per cycle increases, whereas stage 2 begins to account for the majority of NREM sleep. Subsequently the person exits the NREM stage, reversing through the stages to enter the REM sleep state as demonstrated in Figure 3. The average length of the first NREM-REM cycle is 70-100 minutes, whereas the later cycles are slightly longer-lasting – approximately 90 to 120 minutes.Ī sleep episode begins with a period of NREM stage 1 sleep, progressing through stages 2, 3 and 4. Throughout the course of the night, a person will cycle through NREM and REM sleep. Sawtooth waves – low voltage high frequency Rapid eye movements classically absent with stage 4 (the deepest sleep stage) lasting 20-40 minutes Spindles (initiated from the thalamus) and K complex and mixed EEG activity Low-voltage high-frequency beta waves (>14 Hz) The state of being awake and alert with awareness. The table below summarises the different stages of sleep, as well as their associated EEG patterns. In contrast to REM sleep, there is usually little or no rapid eye movement and muscles are not paralysed.Īdditionally, parasympathetic activity prevails – resulting in lowered heart rate, respiration rate and renal function, and increased digestion. This phase of sleep is additionally divided into 4 stages according to the increasing synchronisation of neural activity and lower frequency of generated waves. NREM sleep is characterised by slow, low-frequency EEG patterns. Additionally, during the REM phase, the human brain produces vivid images and events which we know as dreams. Sympathetic activity predominates during this phase of sleep, which in turn results in an increased respiratory and heart rate. The exceptions are respiratory muscles and extraocular muscles. Interestingly, during this sleep phase, almost all muscles of the body are paralysed ( REM atonia). Sleep is divided into two states, which we will now explore in more detail.ĭuring REM sleep, the brain appears more active on an electroencephalogram (EEG) compared to alertness. Licensed under Creative Commonsįig 1 – Circadian rhythms REM vs NREM Sleep ![]() Sleep-Wake Regulation and Its Impact on Working Memory Performance: The Role of Adenosine. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |