Our intelligence, our planning ability, our humaneness—things which make us different from other animals—are more a matter of the superior human nervous system than any other body structure. Perception, consciousness, language, learning, memory, thinking, and the social, creative behaviors produced by them are all functions of the nervous system. Consequently, we begin to worry when we are no longer as alert as we once were, cannot remember things that we did, or experience difficulties with abstractions. Decrements in these functions may not be inevitable consequences of aging, but comparing our mental abilities with how they used to be, or with the abilities of younger adults, older adults often find themselves coming up short.
The basic building blocks of the nervous system are neurons. Neurons increase in size and complexity as the individual matures, but their number and size decrease gradually after then. Age-related changes occur in both the central (brain and spinal cord) and the peripheral nervous system, and particularly in the former. The volume and weight of the brain decline, the gyri or ridges in the brain become smaller, and the fissures become larger. Cerebral blood flow and oxygen and glucose consumption by the brain decline, while the volume of ventricular fluid increases. The number of granules of lipo-fuscin, a pigmented material containing lipids, carbohydrates, and protein, increases with aging. Fatty tissue and calcified material referred to as plaque accumulate in the cerebral blood vessels, and bundles of paired, helical filaments known as neurofibrillary tangles are found in small numbers in normal aged brains and in large numbers in diseased brains.
With respect to behavior regulated by the nervous system, many central nervous system reflexes and responses controlled by the autonomic nervous system become slower or weaker as a person ages. Sleep, which is neither as deep nor as refreshing as it was during the early adult years, decreases in amount. Signs of aging can also be found in the brain waves and in cognitive functions such as short-term memory. Such changes occur at different rates and to different degrees in different people. Age-related decrements in intellectual functioning can be arrested to some degree by intellectual exercise and, in any case, compensated for by careful planning, use of memory aids, and other procedures.
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