Central Nervous System - Reticular Formation

Reticular Formation

Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test

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The Reticular Formation contains a number of neuron groups and fiber tracts that run the full length of the lower brain stem (medulla, pons, and midbrain). The ascending fibers carry information to the cerebellum, hypothalamus, thalamus, limbic system, and cerebral cortex. These connections allow the reticular formation to modulate the activity of neurons diffusely throughout the central nervous system, and thereby regulate both the sleep-wake cycle and levels of arousal and activity while awake. The more active the reticular formation, the more able we are to focus attention on events outside of us. Destruction of these fibers results in coma. Descending fibers from the reticular formation to the spinal cord regulate the perception of pain, breathing, and muscular reflexes.

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The term reticular is derived from the Latin word rete, which means net. This term describes the widespread projections of the ascending portion of the reticular formation (ascending reticular activating system, ARAS) and the high degree of interconnection between neurons within the formation. When examined under magnification, the reticular formation is distinctly more irregular in appearance than the rest of the brain. When the ARAS is stimulated, a sleeping individual is awakened or an individual who is awake becomes more aroused to external events. Damage of the reticular formation results in prolonged sleep or inactivity. The neurotransmitter, norepinephrine, is utilized by this activating region. The ARAS receives input from the cranial nerves and all sensory systems. Strong stimulation from any of these inputs will activate the ARAS, which in turn activates large portions of the cerebral cortex. In addition, the ARAS is capable of generating its own spontaneous activity.