Final answer:
Alzheimer's disease begins in the hippocampus, leading to memory problems, and progresses to involve more widespread areas of the brain. Amyloid plaques and neurofibrillary tangles disrupt neuronal function, contributing to the progressive nature of the disease. These characteristic changes result in cognitive decline and severe brain shrinkage in the later stages of Alzheimer's.
Step-by-step explanation:
In Alzheimer's disease (AD), cells in the brain are impaired in a characteristic pattern, starting in regions critical for memory and cognitive function. One of the earliest areas affected by Alzheimer's is the hippocampus, which is essential for learning and memory, and is why memory problems are often the initial symptom of the disease. The presence of amyloid plaques and neurofibrillary tangles are hallmarks of AD, and they lead to the loss of synapses and eventual death of neurons.
As AD progresses, the damage extends to other areas, leading to further cognitive decline. The cerebral cortex, which is involved in various higher brain functions, also becomes affected, resulting in more widespread symptoms. In severe stages of Alzheimer's, there is widespread neuronal loss and brain shrinkage, particularly in the hippocampus and the ventricles.
Current research continues to explore the molecular and cellular changes associated with AD, including the effects of amyloid β (Aß) peptide and hyperphosphorylated tau protein on neurons. While most cases are sporadic with no known direct cause, a small percentage are linked to genetic factors and classified as Familial Alzheimer's Disease (FAD).