Final answer:
Neurodegenerative diseases commonly involve the accumulation of misfolded proteins within brain cells, causing toxicity and dysfunction, exemplified in conditions such as Alzheimer's and Parkinson's diseases.
Step-by-step explanation:
A common element for neurodegenerative diseases is the presence of misfolded proteins within brain cells. In diseases such as Alzheimer's and Parkinson's, these proteins, which are normally responsible for various cellular functions, begin to fold improperly. This incorrect folding leads to the proteins losing their normal function and instead, they accumulate in the brain, becoming toxic. Specifically, Alzheimer's disease is associated with the accumulation of beta-amyloid plaques, while Parkinson's disease is linked to an abundance of misfolded alpha-synuclein. The term for diseases caused by protein misfolding and accumulation is proteopathy, and it denotes a wide range of diseases beyond the nervous system, suggesting new avenues for therapy and prevention.