<p> PATTERNS OF INJURY IN THE NERVOUS SYSTEM</p><p>The cellular constituents of the nervous system respond in different ways to various forms of injury. </p><p>Markers of Neuronal Injury </p><p>In response to injury, changes can be observed in neurons and their processes (axons and dendrites). Within 12 hours of an irreversible hypoxic/ischemic insult, acute neuronal injury becomes evident even on routine hematoxylin and eosin (H & E) staining . There is shrinkage of the cell body, pyknosis of the nucleus, disappearance of the nucleolus, and loss of Nissl substance, with intense eosinophilia of the cytoplasm ("red neurons"). Often, the nucleus assumes the angulated shape of the shrunken cell body. Areas of cerebral ischemia may progress to coagulative necrosis. Injured axons undergo swelling and show disruption of axonal transport. The swellings (spheroids) can be recognized on H & E stains and can be highlighted by silver staining or immunohistochemistry for axonally transported proteins such as amyloid precursor protein. Axonal injury also leads to cell body enlargement and rounding, peripheral displacement of the nucleus, enlargement of the nucleolus, and dispersion of Nissl substance (from the center of the cell to the periphery, so-called central chromatolysis; ). Many neurodegenerative diseases are associated with specific intracellular inclusions that help in diagnosing the disease (e.g., Lewy bodies in Parkinson disease and tangles in Alzheimer disease). In some neurodegenerative diseases, neuronal processes also become thickened and tortuous; these can be seen as dystrophic neurites. Viral infections can form inclusions in neurons, just as they do in other cells of the body. With age, neurons also accumulate complex lipids in their cytoplasm and lysosomes (lipofuscin).</p><p>. (Brain : ( Liquafactive necrosis – abscess : Lesion 1- There is loss of architecture of the tissue & loss of cellular details. 2- There is necrotic debris of the nuclei & cytoplasm. 3- There is infiltration of dead & live nutrophils. 4- Congestion of blood vessels. Brain : ( Perivascular leukocytic cuffing ). : Lesion There is infiltration of blood leukocytes such as -1 lymphocytes , macrophages , neutrophils around the blood vessels .</p><p>. ( Brain : ( Granuloma : Lesion 1- There is extensive infiltration of mononuclear cells ; lymphocytes , macrophages replacing the brain tissue with central necrosis giving granulomatus lesions . ( caused by salmonella granuloma ) .</p><p>Brain : ( Gliosis ). : Lesion 1- There is focal proliferation of micro-glial cells in the brain tissue . 2- These micro-glial cells are fixed phagocytic cells in the brian .</p>