<Li> Sleep and consciousness--The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert some control over which sensory signals reach the cerebrum and come to our conscious attention . It plays a central role in states of consciousness like alertness and sleep . Injury to the reticular formation can result in irreversible coma . </Li> <Li> Habituation--This is a process in which the brain learns to ignore repetitive, meaningless stimuli while remaining sensitive to others . A good example of this is a person who can sleep through loud traffic in a large city, but is awakened promptly due to the sound of an alarm or crying baby . Reticular formation nuclei that modulate activity of the cerebral cortex are part of the ascending reticular activating system . </Li> <P> The ascending reticular activating system (ARAS), also known as the extrathalamic control modulatory system or simply the reticular activating system (RAS), is a set of connected nuclei in the brains of vertebrates that is responsible for regulating wakefulness and sleep - wake transitions . The ARAS is a part of the reticular formation and is mostly composed of various nuclei in the thalamus and a number of dopaminergic, noradrenergic, serotonergic, histaminergic, cholinergic, and glutamatergic brain nuclei . </P> <P> The ARAS is composed of several neuronal circuits connecting the dorsal part of the posterior midbrain and anterior pons to the cerebral cortex via distinct pathways that project through the thalamus and hypothalamus . The ARAS is a collection of different nuclei--more than 20 on each side in the upper brainstem, the pons, medulla, and posterior hypothalamus . The neurotransmitters that these neurons release include dopamine, norepinephrine, serotonin, histamine, acetylcholine, and glutamate . They exert cortical influence through direct axonal projections and indirect projections through thalamic relays . </P>

What is the function of ras in the brain
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