Anatomy & Physiology

Anatomy & Physiology Study Guide

Reticular Activating System (RAS) Arousal, or awakening from sleep, looks to be one of the functions of the reticular formation. The reticular formation is extremely suitable for providing “watchdog” services because it has widespread interconnections with the sensory, motor, and integrative nuclei and pathways all along the brain stem. The state of consciousness for an individual is determined by complex interactions between the reticular formation and the cerebral cortex. One of the most significant brain stem components is a disperse network in the reticular formation referred to as the reticular activating system (RAS). This network runs from the medulla oblongata to the mesencephalon. Sleep may be ended by any stimulus sufficient to activate the reticular formation and RAS. Arousal occurs quickly, but the impact of a single stimulation of the RAS lasts less than a minute. After many hours of activity, the reticular formation becomes less responsive to stimulation. 15.5 Aging Aging produces various structural and functional changes in the nervous system. Anatomical and physiological changes begin shortly after maturity (probably by age 30) and accumulate over time. Common age-related anatomical changes in the nervous system include a reduction in brain size and weight, a reduction in the number of neurons, a decrease in blood flow to the brain, changes in the synaptic organization of the brain, and intracellular and extracellular changes in CNS neurons. These anatomical changes are linked to functional changes. In general, neural processing becomes less efficient with age. Memory consolidation typically becomes more difficult, and secondary memories become harder to access. The sensory systems of the elderly—notably, hearing, balance, vision, smell, and taste—are less sensitive than those of a younger individual. Reaction rates and reflexes are decreased. The accuracy of motor control slows, and it takes more time to perform a given motor pattern than it did 20 years earlier.

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