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30.6D: Aging and the Nervous System

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    8427
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    One of the effects of aging on the nervous system is the loss of neurons in the cerebral cortex.

     

    LEARNING OBJECTIVES

     

    Describe the effects of aging on the nervous system

     

    KEY TAKEAWAYS

    Key Points

     

    • As the brain ages, neurons in the central nervous system (CNS), which do not typically regenerate, are lost. This reduces the brain’s capacity to send and receive nerve impulses and slows information processing.
    • Dementia is the age-related progressive decline in cognitive function. This may affect memory, attention, language, and problem-solving.
    • Alzheimer’s disease is a neurodegenerative disease characterized by progressive cognitive deterioration, declining activities of daily living, and neuropsychiatric symptoms or behavioral changes. It is the most common cause of dementia.

     

    Key Terms

     

    • cerebral cortex: The gray, folded, outermost layer of the cerebrum that is responsible for higher brain processes such as sensation, voluntary muscle movement, thought, reasoning, and memory.
    • dementia: A progressive decline in cognitive function due to brain damage or disease. Areas particularly affected include memory, attention, judgement, language, and problem solving.

    Neuron loss is an effect of aging on the nervous system. By the age of 30, the brain begins to lose thousands of neurons each day, causing a decreased capacity to send nerve impulses to and from the brain and slowing information processing. In addition, voluntary motor movements slow down, reflex time increases, and conduction velocity decreases.

    Dementia (from Latin de- “apart, away” + mens (genitive mentis) “mind”) is the progressive decline in cognitive function due to damage or disease in the brain beyond what is expected from normal aging. Dementia most commonly affects memory, attention, language, and problem solving, although those in the later stages in this condition may be disoriented in time, place, and person. Symptoms of dementia can be classified as either reversible or irreversible depending upon the etiology of the disease. Less than 10% of all dementia cases are reversible.

    Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive cognitive deterioration, declining activities of daily living, and neuropsychiatric symptoms or behavioral changes. It is the most common cause of dementia. The most striking early symptom is short term memory loss (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression. Older memories are often preserved. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and functions (such as decision-making and planning) closely related to the frontal and temporal lobes of the brain as they become disconnected from the limbic system, reflecting extension of the underlying pathological process.

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    Effects of Alzheimer’s Disease: Comparison of a normal aged brain (left) and the brain of a person with Alzheimer’s (right). Differential characteristics are pointed out in the hippocampus, cerebral cortex, and ventricles.

    The symptoms of Alzheimer’s are triggered by neuron loss and an inflammatory response to the deposition of amyloid plaques and neurofibrillary tangles. Alzheimer’s has a genetic component, and autosomal dominant mutations in three different genes have been identified that account for a small number of cases of familial, early-onset AD. For late onset AD (LOAD), only one susceptibility gene has so far been identified: the epsilon 4 allele of the apolipoprotein E gene. Age of onset itself has a heritability of around 50%.

     

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