Physiology
Sleep is a universal need of all higher life forms including humans, absence of which has serious physiological consequences . There are two main types of sleep, non-rapid eye-movement (NREM) sleep and rapid eye-movement (REM) sleep. As well, two major processes regulate the sleep wake system: one that promotes sleep (process S) and one that maintains wakefulness (process C).
The circadian system (24-hour period of biological activity) is responsible for regulating process C. This process maintains wakefulness and alertness by counteracting process S during the day. Wakefulness is influenced by an ascending arousal system, which includes two major pathways that originate in the upper brainstem, as shown in figure 1. One pathway surges from cholinergic neurons located in the upper pons. This pathway causes the activation of segments of the thalamus that preserve the transmission of sensory information to the cerebral cortex . The other pathway also initiates in the upper brainstem however, it is related to different set of cell groups. |
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The other pathway initiates in cell groups in the upper brainstem. These cell groups contain monoamine neurotransmitters such as norepinephrine, serotonin, dopamine, gamma-aminobutyric acid (GABA) and histamine. Instead of entering the thalamus as the first pathway, these neurotransmitters enter the hypothalamus, to further obtain inputs from nerve cells that contain orexin/hypocretin and melanin-concentrating hormone. Subsequently, these inputs navigate to the basal forebrain where additional inputs are obtained from cells containing acetylcholine. Finally, all the gathered inputs converge to the cerebral cortex promoting the activation and preparation of nerve cells to interpret and analyze incoming sensory information.
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H. R. Colten, B. M. Altevogt, and I. of M. (US) C. on S. M. and Research, “Sleep Physiology,” 2006
Gillette M, Abbott S. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Fundamentals of the circadian system; pp. 131–138.
The Sleep-Wakefulness Cycle -. BrainFacts.org. Online. 29 Nov. 2014.
Gillette M, Abbott S. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Fundamentals of the circadian system; pp. 131–138.
The Sleep-Wakefulness Cycle -. BrainFacts.org. Online. 29 Nov. 2014.