ABSTRACT Reticular formation The reticular formation consists of loose groupings of neurons in the white matter (see Fig. 1.15). Reticular neurons have long axonal connections, and individually, project to the hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord. The neurons are specialized for regulating brain arousal. Some form the reticular activating system, sending continued impulses to the cerebral cortex, affecting consciousness and cortex excitability. This system also filters sensory input, allowing just the most important data to reach consciousness. It is inhibited by the hypothalamic sleep centers, and depressed by alcohol and various drugs. The reticular formation also has motor nuclei, projecting to motor neurons in the spinal cord via the reticulospinal tracts, which help control skeletal muscles as coarse limb movements are made. Cardiac, respiratory, and vasomotor centers of the medulla are reticular motor nuclei, and regulate visceral motor (VM) functions.