Pathways of neurodegeneration - multiple diseases - Ursus arctos (brown bear)

Neurodegeneration is generally defined as progressive, irreversible loss of neurons, which may affect either the peripheral or central nervous system (CNS). Neurodegenerative diseases (NDs) include highly debilitating illnesses, such as Alzheimer (AD), Parkinson disease (PD), amyotrophic lateral sclerosis, Huntington disease, spinocerebellar ataxias, and prion diseases (PrD). The hallmark event, which is thought to be at the root of these diseases, is the progressive accumulation of misfolded protein aggregates. Major basic processes include abnormal protein dynamics due to deficiency of the ubiquitin-proteosome-autophagy system, oxidative stress and free radical formation, endoplasmic reticulum stress, mitochondrial dysfunction and (secondary) disruptions of axonal transport.