د.فراس

• Apoptosis


  A single cell-initiated, gene-directed cellular, self-destructive regulatory mechanism that leads to "programmed" cell death
• Apoptosis


  1. Used during development of nervous system to ensure proper migration and orientation of cell layers and removal of excess embryonic cells

  2. Used to remove "Aged" cells (i.e., cell turnover)

  3. Used to maintain cell number homeostasis in organ systems that have regenerative capacity
• Necrosis


  A process that usually affects groups of cells in contrast to single isolated cells as observed in apoptosis
• Necrosis


  1. Hydropic degeneration

  2. Swelling of mitochondria

  3. Pyknosis and fragmentation of the nucleus

  4. Cell lysis caused by cell membrane damage and the inability of the plasma membrane to control ion and fluid gradients
• Cellular debris associated with necrotic neuronal death will illicit an inflammatory response in contrast to apoptotic neuronal death
• Wallerian degeneration

  Necrosis of nerve fibers starting from myelin sheath
• Nerve injury and recovery

  1. Developing regenerating nerve units

  2. Regenerating units try to grow down the nerve to reinnervate muscle or skin

  3. If they make a correct connection, motor nerve to muscle or sensory nerve to skin, then recovery of muscle function and skin sensation will occur

  4. If regenerating nerve fibers do not make a correct connection then no recovery will occur
• First degree injury (Neurapraxia)


  Recovers quickly within days or up to 3 months, with complete recovery and no lasting muscle or sensory problem
• Second degree injury (Axonotmesis)


  Also has complete recovery but much slower than first degree, as nerve must grow back to reinnervate muscle or skin
• Third degree injury

  Also has slow recovery but only partial recovery, amount depends on factors like scarring and potential mismatching of sensory and motor fibers
• Fourth degree injury

  Dense scar tissue within the nerve completely blocking any recovery
• Fifth degree injury

  Nerve is completely separated (Neurotmesis), requires surgery for recovery
• Sixth degree injury


  Combination of the other types of nerve injury, recovery and treatment will vary
• Meningocele


  A newborn animal with a large skin-covered, soft swelling outside the calvaria, usually on the midline
• Meningoencephalocele


  Has brain tissue in the swelling along with the meninges, more common than meningocele
• Cerebellar hypoplasia


  Reduced size of the cerebellum, caused by parvoviruses, panleukopenia virus, canine parvovirus, pestiviruses, diarrhea virus
• Microscopically there is necrosis and loss of the external granular layer and degeneration and loss of Purkinje cells in cerebellar hypoplasia
• Exencephaly


  Brain tissue that protrudes out of the cranial cavity and is not covered by skin, less common than meningoceles or meningoencephaloceles
• Encephalomalacia


  Necrosis of neurons in brain
• Myelomalacia


  Necrosis of neurons in spinal cord
• Polioencephalomalacia


  Necrosis of neurons in gray matter
• Leukoencephalomalacia


  Necrosis of neurons in white matter
• CNS infarction


  Necrosis of a tissue following obstruction (ischemia) of its arterial blood supply
• The more rapid the onset of ischemia, the more severe the lesion. Sudden obstruction can cause many neurons to die within minutes and other components within hours.
• Gradual reduction in blood flow allows time for anastomotic vessels to dilate and compensate.
• Hemorrhagic infarction

  Lesions affecting the gray matter
• Pale infarction


  Infarction of the white matter
• Cytotoxic edema


  Cell swelling caused by increased intracellular fluid with normal vascular permeability
• Vasogenic edema


  Tissue swelling caused by increased extracellular fluid resulting from increased vascular permeability, most common type of edema in the CNS
• Encephalitis


  Inflammation of the cerebral part of the brain
• Types of inflammatory responses in the CNS

  • Serous to suppurative or purulent (bacteria)
  • Eosinophil (salt poisoning, parasitic larval migration)
  • Lymphocytic, monocytic/macrophage, nonsuppurative, lymphomonocytic, and lymphohistiocytic (viruses, certain protozoa)
  • Granulomatous (fungi, certain protozoa, some higher-order bacteria)
• Brain abscess


  Relatively uncommon, arise following entry of bacteria into the CNS, either from direct extension or hematogenously
• Brain abscesses can be single or multiple, discrete or coalescing, and have varied sizes
• Abscess exudate


  White to gray to yellow, thick to granular, color influenced by pyogenic bacteria
• Abscesses may be walled off by processes of astrocytes and fibrous connective tissue from the pia mater, especially when the abscess results from a penetrating wound
• Microscopic appearance of brain abscesses

  Early lesions consist of clusters of microglial cells, later enlarge and contain variable numbers of neutrophils or macrophages, with necrosis and accumulation of gitter cells
• Numerous gram-positive bacilli can be detected in some brain abscess lesions