How the Brain is Different Flashcards
What is the difference between grey and white matter?
grey matter - numerous cell bodies and relatively few myelinated axons,
white matter - myelinated axon tracts and relatively few cell bodies
Arises from the fact that myelin is white
What are the four glial cell types? What are their functions?
Astrocytes - BBB, structural framework, manages chemical milieu, metabolic support for neurons, supplying glutamate, glial scarring
Oligodendrocytes - myelination (1:50 oligodendrocyte:neuron)
ependymal cells - produce CSF
microglia - macrophages of CNS
In what two ways do neurons respond to injury?
Axonal damage (reversible) - swelling and rounding of cell body, disassembly of RER, fragmentation/disappearance of Nissl bodies, peripheral migration of the nucleus eosinophilic degeneration (irreversible) - cytoplasm becomes eosinophilic (pink), nucleus becomes dark and shrunken (pyknotic)
How do astrocytes respond to injury?
Proliferation of astrocytes and formation of reactive astrocytes that increase production of glial fiber processes. Glial fibers coalesce and form a glial scar made of GFAP (glial fibrillary acidic protein)
No involvement of fibroblasts, no collagen deposition
How do microglia respond to injury?
Microglia get activated and proliferate within 5 days of injury. They encircle degenerating neurons and form clusters (nodules) around necrotic brain tissue and undergo neuronophagia. Then they differentiate into macrophages which phagocytose the debris.
What are the histological characteristics of ependymal cells?
Epithelial-like, ciliated, simple cuboidal cells with microvilli that line the ventricles and the central canal of the spinal cord. Cilia circulates the CSF fluid. Microvilli absorb CSF
Which cell types in the CNS are derived from neuroectoderm? Mesoderm?
Neuroectoderm - neurons, astrocytes, oligodendrocytes, ependymal cells
Mesoderm - microglia, endothelial cells of the capillaries
What are the types of edema that can occur in the brain? How are they different?
Vasogenic edema - failure of the BBB causes water to leak into the extracellular space. Responds to glucocorticoids and osmotic therapy (increasing water excretion in the kidney by infusing mannitol, which is osmotically active but not reabsorbed in the tubules)
Cytotoxic edema - failure of Na+-K+ pump leads to intracellular retention of Na+ and water follows Na+, leading to cellular swelling. The BBB remains intact. Does not respond to glucocorticoids or osmotic therapy.
What are the causes of vasogenic edema? cytotoxic edema?
vasogenic edema - tumors, brain abscesses, trauma, inflammation, HTN
cytotoxic edema - early ischemia/hypoxia, various toxins
What are the clinical manifestations of increased intracranial pressure?
Headache, nausea, vomiting, bradycardia, HTN, loss of consciousness, papilledema
What is the Monro-Kellie Doctrine?
The skull has a fixed volume that contains brain tissue, CSF and blood. An increase in the volume of one of these components will lead to a decrease in the volume of the other components, or else the intracranial pressure will rise. Since central perfusion pressure = mean arterial pressure - intracranial pressure, a rise in ICP will decrease the perfusion of the brain, leading to ischemia injury
What are the differences in multipolar neurons, bipolar neurons and unipolar neurons? Where in the nervous system can each type of neuron be found?
Multipolar neuron - classical neuron with multiple dendrites emanating from the cell body and one axon. Found throughout the CNS
bipolar neurons - looks like a snake that swallowed an egg. Dendrites are distal to the cell body; axon is proximal to the cell body (directed toward the CNS). Found in the retina and the vestibulocochlear nerve (CN VIII)
Unipolar neuron - the cell body is connected by a short segment to a single process. Found in the ganglia of sensory neurons in the PNS, most notably in the dorsal root ganglia
What are the two main categories of neurons based on the shape of their dendrites?
Pyramidal cells - triangular shaped soma; dendrites radiate from one corner of the triangle; dendrites have dendritic spines that are modifiable based on age, experience, learning, memory and hormones
Granule (stellate) cells - dendrites radiate in all direction from the soma.
What are the three main categories of neurons based on the length of their axons?
Projection cells - (long axon)
interneurons - (short axon) also called local circuit neurons. Short enough to stay within the dendritic field of the cell
Amacrine - (no axon) Found in retina and olfactory bulb
What are the two types of astrocytes and where are they found?
Protoplasmic - grey matter
fibrous - white matter
