Alzheimers disease. Conceptual artwork of a brain and nerve cells to depict dementia due to Alzheimers disease. A sagittal slice through the brain is overlain with nerve cells. The nerve cells (neurones) with long axons and dendrites, and cell bodies (triangularshaped), appear tangled. In Alzheimers disease tangled protein filaments occur within the nerve cells and lesions of betaamyloid protein develop. Brain cells also shrink and die (lower right). Alzheimers disease is the most common cause of old age dementia. In this disease there is a general decline in mental ability which progressively worsens over time.