brain, spinal cord, and nerve disorders
Effects of Aging on the Nervous System
 Brain 
Brain function varies normally as people pass from childhood through adulthood to old age. During childhood, the ability to think and reason steadily increases, enabling a child to learn increasingly complex skills. During most of adulthood, brain function is relatively stable. After a certain age, which varies from person to person, brain function declines. Some areas of the brain decrease in size by up to 1% per year in some people but without any loss of function. Thus, age-related changes only in brain structure do not always result in loss of brain function. However, a decrease in brain function with aging may result from numerous factors that include changes in brain chemicals (neurotransmitters), changes in nerve cells themselves, toxic substances that accumulate in the brain over time, changes in blood flow to the brain, and inherited changes. Different aspects of brain function may be affected at different times: Short-term memory and the ability to learn new material tend to be affected relatively early. Verbal abilities, including vocabulary and word usage, may begin to decline later. Intellectual performance—the ability to process information (regardless of speed)—is usually maintained if no underlying neurologic or vascular disorders are present. Reaction time and performance of tasks may become slower because the brain processes nerve impulses more slowly. However, the effects of aging on brain function may be difficult to separate from the effects of various disorders that are common among older adults. These disorders include Depression , As people age, the number of Nerves in the brain may decrease, although the number lost varies greatly from person to person, depending on the person’s health. In addition, some types of memory are more vulnerable to loss, such as memory that holds information temporarily (short-term memory). However, the brain has certain characteristics that help compensate for these losses. Redundancy:The brain has more cells than it needs to function normally. Redundancy may help compensate for the loss of nerve cells that occurs with aging and disease. Formation of new connections:The brain actively compensates for the age-related decrease in nerve cells by making new connections between the remaining nerve cells. Some areas of the brain may produce new nerve cells, especially after a brain injury or a stroke. These areas include the Cerebrum (which is involved in the formation and retrieval of memories) and the basal ganglia (which coordinate and smooth out movements). Thus, people who have had a brain injury or stroke can sometimes learn new skills, as occurs during Occupational Therapy (OT) . People can influence how quickly brain function declines. For example, physical exercise seems to slow the loss of nerve cells in areas of the brain involved in memory. Such exercise also helps keep the remaining nerve cells functioning. On the other hand, consuming 2 or more drinks of alcohol a day can speed the decline in brain function. As people age, blood flow to the brain in some people does not change or decreases only slightly. But in many others, blood flow decreases about less than 1% each year. The decrease in blood flow is greater in people who have atherosclerosis of the arteries to the brain (cerebrovascular disease). This disease is more likely to occur in people who have smoked for a long time or who have High Blood Pressure , Physical exercise may slow the age-related decline in brain function. 