Reticular Activating System

RETICULAR ACTIVATING SYSTEM
  • Origin: midbrain > pons > medulla
  • Extensions: thalamus, hypothalamus, cingulate gyrus, mesial frontal lobes
  • Fx: regulates arousal / sleep-wake transitions
  • In pons (central tegmental tract, pars oralis, pars caudalis, raphe nuclei
    Ascending fibers from reticular formation nuclei --> thalamus
    Descending fibers from midbrain nuclei --> inferior olive. 
  • Reticulospinal fibers descend through brainstem in MLF
    → descend in anterior (pontine) and lateral (medullary) funiculi
    --> MLF
    → terminate in Rexed VII, VIII, and IX of all spinal levels
    majority synapse on interneurons, some medullary RS fibers synapse directly on MNs
  • Corticoreticular fibers influence neurons in reticular formation that give rise to RS Tract
  • Raphe nuclei of RF → serotonergic projections to Rexed I, II, V that elecits analgesic effects by inhibiting afferent nocioceptive inputs
--| Akinetic mutism, Coma
  • Decerebrate posturing:
    Normallly: 
    RAS fibers b/w superior & inferior colliculus --| lateral vesticular nuclei (therefore, flexor)
    If RAS fibers transected --> removal of inhibition --> decerebrate extensor posturing