Neurodegeneration refers to progressive loss of structure and function of neurons, driven by interacting molecular and cellular insults rather than a single cause. A central theme is chronic cellular stress that overwhelms protective mechanisms and pushes vulnerable neurons toward dysfunction and death.

Protein misfolding and aggregation are key features. Misfolded proteins such as amyloid beta, tau and alpha synuclein evade quality control, accumulate in characteristic deposits and disrupt synapses, intracellular transport and signaling. Impaired proteostasis is linked to defective autophagy and ubiquitin proteasome activity, allowing toxic species to persist.

Mitochondrial dysfunction is another major driver. Defects in oxidative phosphorylation, abnormal mitochondrial dynamics and accumulation of mitochondrial DNA damage reduce ATP production and elevate reactive oxygen species. This oxidative stress oxidizes lipids, proteins and nucleic acids, further damaging organelles and triggering apoptotic pathways.

Chronic neuroinflammation contributes to disease progression. Microglia and astrocytes become persistently activated, releasing cytokines, complement factors and reactive species that alter synaptic pruning, impair plasticity and can become directly neurotoxic. This inflammatory milieu interacts with protein aggregates and metabolic dysfunction in a vicious cycle.

Synaptic failure appears early, often preceding overt cell loss. Disrupted calcium homeostasis, receptor trafficking and axonal transport weaken connectivity and information processing. Over time, affected neural circuits show selective vulnerability, helping explain distinct clinical syndromes.

Genetic risk factors and environmental exposures modulate these core processes, shaping susceptibility and disease onset. Emerging therapies therefore target common mechanisms such as enhancing proteostasis, stabilizing mitochondria, dampening maladaptive inflammation and protecting synapses, aiming to slow or halt neurodegenerative cascades across different disorders.