Final answer:
Neurofibrillary tangles are intracellular structures composed of hyperphosphorylated tau proteins. They form within neurons, leading to destabilization of microtubules and neuronal degeneration, which is characteristic of Alzheimer's disease.
Step-by-step explanation:
Neurofibrillary tangles are intracellular structures that form within neurons. They are associated with several neurodegenerative disorders, including Alzheimer's disease. Neurofibrillary tangles result from the abnormal accumulation and hyperphosphorylation of the tau protein, which, under normal conditions, is essential for stabilizing microtubules within the neuronal cytoskeleton. When tau proteins become hyperphosphorylated, they lose their ability to stabilize microtubules, leading to collapse of the microtubule network and subsequent formation of neurofibrillary tangles.
These tangles comprise deformed tau proteins that clump together inside neurons, and this aggregation is detrimental to neuron health and function. The presence of neurofibrillary tangles, along with extracellular amyloid plaques, is a hallmark sign of Alzheimer's disease, contributing to the progressive death and degeneration of neurons, loss of connectivity, and resulting cognitive decline.