Effects of Aging on the Brain

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Chapter: Anatomy and Physiology for Health Professionals: Central Nervous System

Aging of the CNS begins before birth, as ­programmed cell death (apoptosis) determines which structures will remain in the brain. Neurons continually die throughout life.


Effects of Aging on the Brain

Aging of the CNS begins before birth, as ­programmed cell death (apoptosis) determines which structures will remain in the brain. Neurons continually die throughout life. When apoptosis of the brain fails, disease develops such as in the brains of schizo-phrenics. Their brains, in young adulthood, have the same numbers of neurons as those of newborn babies. These extra amounts of neurons produce excessive dopamine, which can cause the halluci-nations that are so prevalent in this disease. After young adulthood, brain neurons of all individuals start to become damaged and die. However, only a small percentage of total brain neurons are actually lost. Continued learning throughout the life span occurs because the remaining neurons can alter their synaptic connections.

By approximately age 30, neuron death increases in speed. However, pockets of neural stem cells that line the ventricles are still able to create cells that differentiate­ into neurons and neuroglia. In most individuals, the brain shrinks by about 10% over the lifetime, with more gray matter lost than white mat-ter. There is an uneven loss of neurons. While many cells die in the temporal lobe, very few die in the brain stem. By the age of 90, nearly half of the neurons of the frontal cortex have been lost; yet, this does not mean that function is necessarily impaired.

In elderly people, the brain becomes reduced in both size and weight, which is linked to loss of the cortical­ neurons. The synaptic organization of the brain changes as the number of dendritic branches and other structures decreases. This limits neu-rotransmitter production. Brain neurons accumulate abnormal intracellular deposits. Extracellular plaques may affect memory processing. When deposits and plaques exceed normal amounts caused by aging, ­clinical abnormalities may occur.

Aging does cause cognitive declines that may affect perception speed, spatial abilities, making decisions, reacting to occurrences, and memory loss. Cognitive declines usually only become ­significant when a person is in his or her 70s. ­Functions that do not decline with age include fluency of speech and mathematical skills. Reversible dementia may be caused by adverse effects of medications, poor ­nutrition, low blood pressure, hormone imbal-ances, dehydration, and depression. Alcoholics and athletes who experience head trauma experience greater loss of brain size and weight and at much earlier ages.

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