망상 활성계

뇌간 각성계(brainstem activating systems) 또는 망상 활성계(reticular activating system, RAS)또는 망상체 활성화계(網狀體活性化系) 또는 망상활성화시스템은 뇌간에 집중되어 기반한 시스템으로 이는 뇌 전체 영역으로 널리 퍼지는 작용 및 기능에서 뇌의 각성, 흥분, 집중 등에 관여한다. 이러한 맥락에서 또는 상승 망상체 활성화 시스템(ARAS,ascending reticular activating system)이라고도 한다. 후뇌에서 시작하여 상부의 중뇌에 이르는 망형 구조를 이루며 이 신경작용이 전뇌에까지 널리 퍼져 이르를수있는 대뇌피질투영(cortical projection)으로 알려진 이러한 과정에서 의식의 여부를 조절하게 된다. 망상 활성계의 주요 기능은 시상대뇌피질에서의 뇌전도 불일치를 조절하는 것으로 알려져 있다.

만약 외과적 수술에 의해 망상 활성계가 파괴된다면 해당 동물은 장시간 혼수상태에 빠지게 된다. 또한 일반적인 마취에서 마취제는 망상 활성계내에서 신경전달을 억제한다. 이러한 실험적 증거로 인해 뇌의 각성상태 유지에 망상 활성계가 중요하다는 사실이 밝혀졌다.[1]

특히 망상체 활성화 시스템은 뇌간 내에서의 여러 신경핵과 섬유 전도로들이 복잡한 그물망을 형성하고 있는 망상체및 이와 네트워크된 여러 신경핵들을 가리킨다. 감각 정보의 유입에 대해 대뇌를 비특이적으로 각성시킨다. 의식이 깨어 있게 하거나 대뇌의 의식적 활동과 함께 비의식적 활동을 매개하거나 수면 및 각성에서 조절되어 있는다.

뇌핵편집

시상외 제어 조절 시스템(the extrathalamic control modulatory system) 또는 상승 망상체 활성화 시스템(ARAS,ascending reticular activating system)으로도 알려진 망상 활성화 시스템(RAS)은 수면 및 수면 깨우기(각성) 전이를 조절하는 척추 동물의 뇌에 연결된 핵 세트이다. RAS는 망상 형성의 일부이며, 시상의 다양한 핵과 연관되어 도파민 성, 노르에피네프린 성, 세로토닌 성, 콜린성의 주요 신경전달물질 생성및분비에 관여하며 히스타민글루타메이트 성 뇌핵으로 구성된 경우도 있다.[2][3][4][5]

주요 뇌핵편집

흑질(substantia nigra), VTA(ventral tegmental area), 청반(locus c(o)eruleus), 봉선핵(Raphe nuclei), 적핵(Red nucleus), 전정핵(앞뜰핵), 앞뇌기저핵(nucleus basalis)등이 있다.

같이 보기편집

각주편집

  1. Silverthorn, Dee Unglaub, Ph.D., Ober, William C., Garrison, Claire W., Silverthorn, Andrew C., M.D. , 《Human Physiology》, Addison-Wesley, 2008. 03. 01
  2. Iwańczuk W, Guźniczak P (2015). “Neurophysiological foundations of sleep, arousal, awareness and consciousness phenomena. Part 1”. 《Anaesthesiol Intensive Ther》 47 (2): 162–167. doi:10.5603/AIT.2015.0015. PMID 25940332. The ascending reticular activating system (ARAS) is responsible for a sustained wakefulness state. It receives information from sensory receptors of various modalities, transmitted through spinoreticular pathways and cranial nerves (trigeminal nerve — polymodal pathways, olfactory nerve, optic nerve and vestibulocochlear nerve — monomodal pathways). These pathways reach the thalamus directly or indirectly via the medial column of reticular formation nuclei (magnocellular nuclei and reticular nuclei of pontine tegmentum). The reticular activating system begins in the dorsal part of the posterior midbrain and anterior pons, continues into the diencephalon, and then divides into two parts reaching the thalamus and hypothalamus, which then project into the cerebral cortex (Fig. 1). The thalamic projection is dominated by cholinergic neurons originating from the pedunculopontine tegmental nucleus of pons and midbrain (PPT) and laterodorsal tegmental nucleus of pons and midbrain (LDT) nuclei [17, 18]. The hypothalamic projection involves noradrenergic neurons of the locus coeruleus (LC) and serotoninergic neurons of the dorsal and median raphe nuclei (DR), which pass through the lateral hypothalamus and reach axons of the histaminergic tubero-mamillary nucleus (TMN), together forming a pathway extending into the forebrain, cortex and hippocampus. Cortical arousal also takes advantage of dopaminergic neurons of the substantia nigra (SN), ventral tegmenti area (VTA) and the periaqueductal grey area (PAG). Fewer cholinergic neurons of the pons and midbrain send projections to the forebrain along the ventral pathway, bypassing the thalamus [19, 20]. 
  3. Malenka RC, Nestler EJ, Hyman SE (2009). 〈Chapter 12: Sleep and Arousal〉. Sydor A, Brown RY. 《Molecular Neuropharmacology: A Foundation for Clinical Neuroscience》 2판. New York, USA: McGraw-Hill Medical. 295쪽. ISBN 9780071481274. The RAS is a complex structure consisting of several different circuits including the four monoaminergic pathways ... The norepinephrine pathway originates from the locus ceruleus (LC) and related brainstem nuclei; the serotonergic neurons originate from the raphe nuclei within the brainstem as well; the dopaminergic neurons originate in ventral tegmental area (VTA); and the histaminergic pathway originates from neurons in the tuberomammillary nucleus (TMN) of the posterior hypothalamus. As discussed in Chapter 6, these neurons project widely throughout the brain from restricted collections of cell bodies. Norepinephrine, serotonin, dopamine, and histamine have complex modulatory functions and, in general, promote wakefulness. The PT in the brain stem is also an important component of the ARAS. Activity of PT cholinergic neurons (REM-on cells) promotes REM sleep. During waking, REM-on cells are inhibited by a subset of ARAS norepinephrine and serotonin neurons called REM-off cells. 
  4. Brudzynski SM (July 2014). “The ascending mesolimbic cholinergic system--a specific division of the reticular activating system involved in the initiation of negative emotional states”. 《Journal of Molecular Neuroscience》 53 (3): 436–445. doi:10.1007/s12031-013-0179-1. PMID 24272957. Understanding of arousing and wakefulness-maintaining functions of the ARAS has been further complicated by neurochemical discoveries of numerous groups of neurons with the ascending pathways originating within the brainstem reticular core, including pontomesencephalic nuclei, which synthesize different transmitters and release them in vast areas of the brain and in the entire neocortex (for review, see Jones 2003; Lin et al. 2011). They included glutamatergic, cholinergic, noradrenergic, dopaminergic, serotonergic, histaminergic, and orexinergic systems (for review, see Lin et al. 2011). ... The ARAS represented diffuse, nonspecific pathways that, working through the midline and intralaminar thalamic nuclei, could change activity of the entire neocortex, and thus, this system was suggested initially as a general arousal system to natural stimuli and the critical system underlying wakefulness (Moruzzi and Magoun 1949; Lindsley et al. 1949; Starzl et al. 1951, see stippled area in Fig. 1). ... It was found in a recent study in the rat that the state of wakefulness is mostly maintained by the ascending glutamatergic projection from the parabrachial nucleus and precoeruleus regions to the basal forebrain and then relayed to the cerebral cortex (Fuller et al. 2011). ... Anatomical studies have shown two main pathways involved in arousal and originating from the areas with cholinergic cell groups, one through the thalamus and the other, traveling ventrally through the hypothalamus and preoptic area, and reciprocally connected with the limbic system (Nauta and Kuypers 1958; Siegel 2004). ... As counted in the cholinergic connections to the thalamic reticular nucleus ... 
  5. Schwartz MD, Kilduff TS (December 2015). “The Neurobiology of Sleep and Wakefulness”. 《The Psychiatric Clinics of North America》 38 (4): 615–644. doi:10.1016/j.psc.2015.07.002. PMC 4660253. PMID 26600100. This ascending reticular activating system (ARAS) is comprised of cholinergic laterodorsal and pedunculopontine tegmentum (LDT/PPT), noradrenergic locus coeruleus (LC), serotonergic (5-HT) Raphe nuclei and dopaminergic ventral tegmental area (VTA), substantia nigra (SN) and periaqueductal gray projections that stimulate the cortex directly and indirectly via the thalamus, hypothalamus and BF.6, 12-18 These aminergic and catecholaminergic populations have numerous interconnections and parallel projections which likely impart functional redundancy and resilience to the system.6, 13, 19 ... More recently, the medullary parafacial zone (PZ) adjacent to the facial nerve was identified as a sleep-promoting center on the basis of anatomical, electrophysiological and chemo- and optogenetic studies.23, 24 GABAergic PZ neurons inhibit glutamatergic parabrachial (PB) neurons that project to the BF,25 thereby promoting NREM sleep at the expense of wakefulness and REM sleep. ... The Hcrt neurons project widely throughout the brain and spinal cord92, 96, 99, 100 including major projections to wake-promoting cell groups such as the HA cells of the TM,101 the 5-HT cells of the dorsal Raphe nuclei (DRN),101 the noradrenergic cells of the LC,102 and cholinergic cells in the LDT, PPT, and BF.101, 103 ... Hcrt directly excites cellular systems involved in waking and arousal including the LC,102, 106, 107 DRN,108, 109 TM,110-112 LDT,113, 114 cholinergic BF,115 and both dopamine (DA) and non-DA neurons in the VTA.116, 117