In some brain diseases such as Alzheimer's, distorted proteins behave like infectious agents,
spreading among brain cells and corrupting other proteins.
It is particularly difficult to control because it does not grow as a round, well - circumscribed mass — instead, because astrocytes» main job is to travel
among the neurons, it is able to send out fingerlike projections throughout the
brain, essentially creating tiny, multiple «highways» that
spread malignant
cells with extreme efficiency.