<prompt> All are true about reticular activating system except?Involved in arousalPolysynaptic pathwayReceives collateral from all sensory pathwayProduces a-block on EEG  <response>: Ans. is d i.e., Produces a-block on EEGReticular activating system RAS is the ascending polysynaptic pathway that extends from brainstem reticularformation to non-specific thalamic nuclei intralarninar and midline nuclei and projects diffusely to cerebral coex.Long sensory tracts give collateral to the RAS, as they ascend in brainstem. Thus RAS receives inputs from the medial and trigeminal leminisci as well as from the visual, auditory and olfactory systems.Therefore, the RAS is a non-specific system which can be excited by any sensation.Activation of RAS causes activation of cerebral coex and arousal from sleep.On arousal from sleep, the EEG pattern changes to high frequency low voltage activity b - wave from high voltage slow waves d - waves of sleep - d-block not a-block. 