Effects of Aging on the Nervous System

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Chapter: Anatomy and Physiology for Health Professionals: Control and Coordination: Neural Tissue

The neural tissues arise from the ectoderm, in response to its adjacent layer, the mesoderm.

Effects of Aging on the Nervous System

The neural tissues arise from the ectoderm, in response to its adjacent layer, the mesoderm. Neural tissues form and develop connections during the embryonic period. Neurons are produced along the central canal, in the neural tube. They later move to their necessary locations, before birth. Axons and dendrites extend from nerve cells to their intended targets. The human brain takes many years before it is completely developed. During fetal development, a child’s head is much larger than the remainder of the body. As periods­ of growth occur, the brain develops very quickly. After birth, up to the age of three years, the brain triples in weight and establishes approxi-mately 1,000 trillion nerve connections. Development of the frontal lobe increases greatly between six and 12 months of age. The prefrontal cortex portion of the frontal lobe is the final brain area to mature, resulting in developmental changes as late as adolescence. This area is the location of cognitive functions that include attention, motivation, and goal-directed behavior.

Beginning at age 30, anatomic and physiological changes begin to affect the nervous system. After age 65, there may be noticeable changes in CNS function and mental performance. As fatty deposits accumulate in the blood vessels, there is a decrease in blood flow to the brain. This can increase the chances that an affected vessel will rupture, leading to symptoms of a stroke (cerebrovascular accident). ­Cerebrovascular diseases are more common in long-term smokers­ or when conditions such as hypertension, high ­cholesterol, or ­diabetes mellitus are present.

Verbal abilities often begin to decline at ­approximately age 70. If no neurologic disorders are present, intellectual performance is usually ­maintained until about age 80. Because the brain processes nerve impulses more slowly, performance of certain tasks and reaction times often become slower. Other dis-orders that affect the nervous system due to aging include depression, hypothyroidism, and degenera-tive brain disorders. An elderly person who exercises (both mentally and physically) often loses fewer nerve cells in the brain. Consumption of two or more drinks of alcohol every day reduces brain function.

The spine is also affected by aging, and pressure increases on the spinal cord and spinal nerve roots. This can result in decreases in sensation, strength, and balance. Peripheral nerve conduction slows because the myelin sheaths degenerate with aging. Self-repair of damaged peripheral nerve cells is also slower in older individuals.

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