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IB. Neurons - pathological changes

Neurons - Pathological reactions

Neurons are more sensitive to injury than other cell types in the CNS. There may be selective vulnerability of groups of neurons to specific types of processes. The following information describes types of neuronal reactions occurring in various disorders. More information will be supplied under specific conditions in which the changes occur. 

1. Necrosis
Necrosis refers to a set of morphological changes that follow cell death. The histological appearance is primarily the result of two processes: enzymic digestion of the cell and denaturation of proteins. In the brain, liquefactive necrosis often occurs (rather than coagulative necrosis in which general tissue architecture is preserved in hypoxic death of cells in all tissues except the brain). Liquefactive necrosis describes dead tissue that appears semi-liquid as a result of dissolution of tissue by the action of hydrolytic enzymes released from lysosomes.   

2. Apoptosis
Apoptosis, a form of programmed cell death, involves different cellular mechanisms than necrosis. Apoptosis is an energy-dependent process designed to switch cells off and eliminate them. Although apoptosis is a physiological process occurring normally during development, it can also be induced by pathological conditions ranging from a lack of growth factor or hormone, to a positive ligand-receptor interaction, to specific injurious agents. The process consists of four major components: (i) signaling pathways; (ii) control and integration mechanisms, in which the Bcl-2 family is important; (iii) an execution phase often involving the caspase family of proteases; (iv) removal of dead cells by phagocytosis.