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Retired NBME 16 Answers

nbme16/Block 1/Question#16 (reveal difficulty score)
A 53-year-old man is brought to the emergency ...
Microglial cells ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—cassdawg(1781)
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Microglia are phagocytic cells and are responsible for clearing debris/necrotic tissue as well as releasing inflammatory mediators (FA2020 p493)

  • Astrocytes are the most common glial cell in the CNS and are responsible for generation of the blood brain barrier as well as for reactive gliosis in damage (FA2020 p493)
  • Important things to know about the neuron reaction to damage would be that the cell body undergoes chromatolysis after axonal injury and distal to the site of injury the axon undergoes Wallerian degeneration. (FA2020 p495)
  • Oligodendrocytes are the myelin sheath forming cells of the CNS.
  • Satellite cells are basically the peripheral nervous system version of astrocytes and have a supportive nutritive function in the PNS.
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fatboyslim  ^Also, just to clear up any confusion about nomenclature (I used to be confused also): The neuron responds to injury in 2 ways, either "acute neuronal injury" or "axonal reaction (AKA chromatolysis)". Acute neuronal injury happens when there is severe damage to the neuron (e.g. ischemia, severe hypoglycemia) leading to cell DEATH. Histology of "acute neuronal injury": you will see shrinkage of the cell body, pyknosis of the nucleus, loss of Nissl substance, and eosinophilic cytoplasm. "Axonal reaction" (AKA chromatolysis) occurs when there is transection of the AXON. The neuron does NOT die. Instead it tries to fix the damage to the axon. So the neuron cell body makes it its mission to ramp up protein production to grow the transected axon, and to do that you need more RER (called Nissl substance in neurons) and the nucleus moves out the way and gets pushed to the side so that the cell body can get to work. +1
fatboyslim  ^ (continued) Also the axon distal to the site of transection breaks down (Wallerian degeneration). Histology of "axonal reaction (AKA chromatolysis)": Enlargement of the cell body, eccentrically placed nucleus, enlargement of the nucleus, dispersion of Nissl substance. (Source: UW 492) +



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