One of the effects of aging on the nervous system is the loss of neurons. By the age of 30, the brain begins to lose thousands of neurons each day. The cerebral cortex can lose as much as 45% of its cells and the brain can weigh 7% less than in the prime of our lives. Associated with the loss of neurons comes a decreased capacity to send nerve impulses to and from the brain. Because of this the processing of information slows down. In addition the voluntary motor movements slow down, reflex time increases, and conduction velocity decreases.
Parkinson's disease is the most common movement disorder of the nervous system. As the brain ages there are also some degenerative changes along with some diseases involving the sense organs that can alter vision, touch, smell, and taste. Loss of hearing is also associated with aging. It is usually the result of changes in important structures of the inner ear.
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 might be expected from normal aging. Particularly affected areas may be memory, attention, language, and problem solving, although particularly in the later stages of the condition, affected persons 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 dementias are reversible.
Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive cognitive deterioration together with 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, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and those 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.
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.
This consists principally of neuronal loss or atrophy, together with an inflammatory response to the deposition of amyloid plaques and neurofibrillary tangles. Genetic factors are known to be important, 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%.