Ascending reticular activating system ARAS

Ascending inputs from the brainstem ascending reticular activating system (ARAS). As described below, these seem to be particularly important and probably disrupt the thalamo-cortical synchrony. 

Figure 22.5 Pathways involved in cortico-thalamic synchrony and EEG arousal. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and midbrain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). Its stimulation is followed by EEG arousal. It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state...

Ascending Reticular Activating System (ARAS) A network of neurons running up (ascending) through the core of the brainstem to the diencephalon and descending to the spinal cord. Also known as the reticular formation. 

In animals, destruction of the ascending reticular activating system (ARAS) induces a state of coma (Moruzzi and Magoun 1949). In men the ARAS is located in the paramedian tegmentum of the dorsal pons and the midbrain extending as a complex polysynaptic system from the upper half of the pons through the midbrain to the dorsal part of the hypothalamus and to the thalamic reticular formation (Vincent 2000). 

Sleep is no longer ccmsidered to be a passive relaxation of the ascending reticular activating system (ARAS), but rather the result of active influences originating from hypnogenic structures. 5-HT neurons are implicated in the physiology and the biochemistry of sleep. 

ARAS ascending reticular activating system CHE cholinesterase... 

Fig. 7. Neurophysiology of sleep in the cat. (A) Schematic view of cerebral structures involved. ARAS ascending reticular activating system RF reticular formation LC locus coeruleus MFB medial forebrain bundle. (B) Polygraphic recordings of electrophysiological events during waking and during the two kinds of sleep. Each line represents 1 min of recordine amplitude calibration SO mv.

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