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63 Cards in this Set
- Front
- Back
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How are brain tumors classified?
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Based upon the resemblance of the predominant tumor cell to a normal cell of the immature or mature nervous system including:
-- astrocytomas -- oligodendrogliomas -- ependymomas |
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What are the cellular elements of the nervous system?
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1. neurons
2. glia -- astrocytes -- oligodendroglia -- microglia 3. ependymal cells |
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gray vs. white matter?
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GRAY: contains neurons
-- spongiform encephalopathies -- neuronal degen diseases WHITE: myelinated axons -- multiple sclerosis |
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Define and describe neuron.
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The first cellular element of the nervous system; neuroectodermal origin; SIGNATURE of the nervous system
May be layered in horizontal rows or laminated (cerebral cortex) May present as prominent grouped structures, particularly in the subcortical areas, designated as ganglia or nuclei, including: -- basal ganglia of cerebrum -- cranial nerve nuclei of brainstem -- nuclei of spinal cord |
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Describe neurons of the cerebral cortex.
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Laminated neurons are frequently
-- triangular or pyramidal in configuraion -- POLARIZED, with apex pointing toward brain surface and base facing downward, toward subadjacent white matter -- myelinated axon arises from base to enter the white matter |
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What is cortical dysplasia?
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an abnormality assoc w/ seizure disorder
-- total disarray of cortical neurons including loss of lamination and polarization, resulting in a jumbled, disorderly pattern |
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The neuron is characterized by...
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IMMENSE CELLULAR PROPORTIONS
-- on e of the largest cells in the body, measuring well over 50 micra -- some, such as Betz cell fo motor cortex, may reach 90 micra in size -- RBC is approx 7 micra |
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Neuron configuration?
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triangular
pyramidal stellate round to oval All depending on location |
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Neuron nucleus?
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large, round, vesicular and clear and contains prominent NUCLEOLUS
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Neuron cytoplasm?
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Abundant cytoplasm comtaining dark blue NISSL MATERIAL
In motor neurons: -- distributed in course clumps -- designated NISSL BODIES In sensory neurons: -- distributed evenly w/in the cytoplasm -- designated NISSL SUBSTANCE |
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The neuronal cytoplasm forms...? What stain illustrates these structures?
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elongated cytoplasmic processes which are not visible on H&E stain
HEAVY METAL STAINS of ionic solutions of silver or gold show the processes |
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The single axon represents...?
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Efferent limb of the neuron from which impulses emanate
-- destined for other neurons |
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Multiple dendrites represent...?
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afferent limbs of the neuron, which receive impulses from other neurons
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The synapse represents...?
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The interneuronal point of contact, subserving coordinated neuronal discharge among interrelated relay systems as basis for harmonious, regulated communication w/in the nervous system
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What is FACITATION?
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positive presynaptic impulses converging on a second or tertiary order neuron from other primary neuronal sources, promoting discharge of an impulse, or firing
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What is INHIBITION?
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negative presynaptic impulses converging on a second or tertiary order neuron from other primary neuronal sources, preventing discharge or firing
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What is SUMMATION?
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refers to the sum total of pre-synaotic positive and negative impulses converging on secondary or tertiary order neuron; if sum total is positive, neuron will fire and vice-versa
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What is the FINAL COMMON PATHWAY?
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implies convergence of several presynaptic impulses from multiple neuronal sources upon a second or tertiary order neuron, determining whether or not the neuron will fire
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The neuron theory?
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1. Neurons are separate and distinct cell entities
2. They conform to the cell theory, as applicable to other tissue 3. The axons and dendrites are contiguous w/ each other and w/ the cell bodies of other neurons i.e. they are distinct and separate entities 4. They are NOT continuous, as in a syncytium 5. Contiguous neurons make contact w/ each other via synapses 6. The complex cellular substrate of the nervous system subserves the fxn of communication via facilitating and inhibiting relays regulated by sensory input from the environment; and by executing appropriate motor commands in response to environmental stimuli, in the ultimate interest of survival of the individual and the species. It interacts and regulates all other organ systems |
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Acute neuronal injuty
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Represents a variant of coagulation necrosis
Characterized by shrinkage (pyknosis) of the neuron Hypoxic ischemic injury represents common and frequent cause |
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Coagulation necrosis of a neuron reflects...?
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irreversible injury
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When is irreversible injury visible?
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12+ hours post-insult via light microscopy
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What is the cytologic configuration of irreversible neuronal injury?
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"Dead-Red Neuron"
3. entire cell shrinks (pyknosis) 2. cytoplasm loses its cell detail and assumes a diffuse, brick-red discoloration (red neuron) 3. nucleus shrinks and loses its cellular detail |
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What is NEURONOPHAGIA?
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Engulfment and ingestion of a neuron by a macrophage
-- Dead-Red Neurons Associated w/ neuronal death, is also referred to as a "glial nodule" |
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What is FERRUGINIZATION or MUMMUFICATION of neurons?
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Occurs predominantly as result of injury to the CNS of a fetus or infant
Dead neurons are NOT removed by macrophages, but become coated w/ mix of calcium, protein, and iron, designated as MINERALIZATION, ferruginization, or mummification |
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In what areas can the earliest evidence of hypoxic-ischemic injury be observed?
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BORDER ZONES or WATERSHED AREAS
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What are the three important Border Zone Areas?
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1. Parasaggital region of the cerebral cortex, approx 1 inch lateral to the sagittal fissure
-- border zone btwn anterior and middle cerebral arteries 2. Hippocampal region of the temporal lobe -- border zone btwn middle and posterior cerebral arteries 3. Apex of the cerebellar convexity -- border zone btwn superior and inferior cerebellar arteries |
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What is PATHOCLISIS?
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Selective vulnerability
Explains the proclivity of neurons at certain sites in the CNS to be more readily injured than in other areas. Implies that these neurons are characterized by an inherent susceptibility to injury, based on intrinsic physiological, chrmical, or molecular differences Other explanations include anatomical differences, such as the tenuous terminal arterial supply characterizing the Border Zones |
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What does an AXONAL REACTION represent?
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Represents a retrograde response of the cell body of the neuron due to injury of the axon proximate to the body of the neuron of origin.
EX: high leg amputation may lead to axonal rxn in anterior horn cells of lumbo-sacral region |
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Describe the axonal reaction.
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1. Primary or first order neuron of origin for the damaged axons swell
2. Nissl bodies of the cytoplasm are dispersed and remain invisible to light microscopy -- prominent in central area of cytoplasm, referred to as CENTRAL CHROMATOLYSIS 3. Nucleolus migrates to edge of nucleus Entire cell resembles a "FISH EYE" |
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What is transsynaptic degeneration?
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An example of neuronal swelling as a reaction to injury; potentially reversible
Rx of a second order neuron to injury of an axon from a first order neuron, destined to synapse upon it. -- injury occurs to the axon of the pre-synaptic first order neuron -- post-synaptic, or second order neuron swells |
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What is “Hypertrophy of the Olive?”
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This is an example of transsynaptic degeneration
-- Descending axon from pre-synaptic or first order cortical neuron, destined to snapse on neuron in inferior olivary nucleus of the brainstem, is injured -- Second order neuron in the olivary nucleus will swell If enough presynaptic, descending axons be injured, entire inferior olivary nucleus may swell in concert w/ diffuse enlargement of entire structure, designated, Hypertrophy of the Olive |
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Another example of transsynaptic degeneration?
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First order, presynaptic ganglion cells of the eye are injured, as in eye removal
-- second order or post-synaptic neurons of the lateral geniculate body will swell in a well-defined sequence |
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Types of neuronal pigment?
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Lipofuscin
Neuromelanin Does NOT parallel the melanin pigment of the skin |
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Lipofuscin?
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Yellow-tan intracytoplasmic neuronal pigment which increases w/ age
Thought to represent benign, “wear-and-tear” phenomenon |
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Neuromelanin?
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Normal intracytoplasmic pigment found in specific nuclei:
-- Substantia Nigra of midbrain -- Locus Coeruleus of the upper pons -- Dorsal Motor X (Vagus) nucleus of the medulla Does not parallel the melanin pigment of the skin -- present in albinos -- lost, with gross depigmentation of the pigmented nuclei, in Parkinson’s disease |
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The melanin content of the ________ parallels the melanin content of the skin?
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Leptomeninges
-- dark in brunettes -- absent in albinos |
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What are causes of neuronal inclusions?
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May result from variety of causes, including degenerative diseases and infections, particularly of viral etiology
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What is a Negri body?
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Intracytoplasmic inclusion
-- due to Rabies (rhabdovirus) |
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What is a Cowdry Type A Intranuclear Inclusion?
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Large reddish-purple (magenta) intranuclear inclusion which displaces the chromatin to the nuclear edge
-- characteristic of certain viral diseases |
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Differential when we see a Cowdry Type A Intranuclear Inclusion?
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1. Progressive Multifocal Leukoencephalopathy (PML)
-- JC (Polyoma) virus 2. Subacute Sclerosing Encephalitis -- Dawson’s encephalitis -- measles virus 3. Herpes simplex 4. Herpes zoster -- chickenpox virus |
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What is glia?
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Term means “glue”
Non-neuronal cellular elements of the CNS were collectively designated as glia -- Now know that it is only the astrocyte, with its delicated, interdigitated cytoplasmic processes, which glues the CNS together |
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How can we see the cytoplasm of glial cells?
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NOT visible with H&E
HEAVY METAL STAINS used to differentiate cytoplasmic processes of neurons and glia, including their intracellular relationships and connections |
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What is an astrocyte?
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Represents the second cellular element of the nervous system; neuroectoderm origin
-- small round nucleus and salt and pepper chromatin pattern w/ H&E stain -- heavy metal ionic solutions or GLIAL FIBRILLARY ACID PROTEIN stains illustrate abundance of delicate cytoplasmic processes radiating from the cell body giving appearance of star Protoplasmic astrocytes: -- located in gray matter -- are characterized by a plump cell body and cytoplasmic processes Fibrillary astrocytes: -- in white matter -- spindled cell bodies and thin cytoplasmic processes |
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What is NEUROPIL?
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Formed from the delicate cytoplasmic processes of an astrocyte which interdigitate to form the delicate, finely fibrillar neuropil in which neurons are embedded, much like raisins in a loaf of bread
-- axons and dendrites of the neurons course, invisible w/ H&E through the neuropil |
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What is GLIOSIS?
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Non-specific response of astrocytes to injury or any kind, resulting in swelling and visibility of the cytoplasm, which assumes a pinkish-red color
-- nucleus is eccentric Protoplasmic astrocyte reacts acutely to injury, as with infarction Fibrillary astrocytes react in chronic mode, as in MS Injury to cerebellum results in activation of astrocytes w/in the plane of Purkinje cells; as Purkinje cells are lost, the reactive glia line up like soldiers at attention Astrocytes in this layer are referred to as BERGMANN’S GLIA or BERGMANN’S GLIOSIS |
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Rosenthal fibers?
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Thick, red linear structures resembling plump, red sausages w/ H&E
Ultrastructural level intracellular, representing swollen astrocyte processes filled w/ glial filaments May be seen adjacent to a variety of lesions as a non-specific reaction to injury and are also characteristically seen in assoc w/: -- PILOCYTIC ASTROCYTOMAS -- CRANIOPHARYNGIOMAS -- ALEXANDER’S DISEASE |
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Corpora amylacea?
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Amyloid bodies
-- round, gray-blue structures w/ concentric rings, which increase in proportion to age -- Prominent beneath pial and subependymal surfaces and around blood vessels -- Intracellular at the ultrastructural level, reflecting deposition of a material resembling glycogen, designated as polyglycosan, w/in the astrocyte |
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What is LaFora’s Disease?
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LaFora bodies are present in a variety of organs, including the CNS
-- depositions of polyglycan may be seen in this systemic storage disease -- the polyglycan is similar to that found in the corpora amylacea |
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What is an oligodendroglial cell?
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Third element of the nervous system (combined w/ microglia)
-- Neuroectodermal origin -- glia w/ few cytoplasmic branches or processes -- forms myelin sheath by wrapping its cytoplasm around the axon in multiple, concentric lamellae -- analogous to Schwann cell of PNS -- does not “glue” the nervous system together w/in a matrix like the astrocyte, so not a “glial” cell in the true sense of the word |
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Morphological characteristics of an oligodendroglia cell with H&E stain?
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1. presence of small, round, dark “cookie cutter” nucleus, resembling a lymphocyte
2. Nucleus may be surrounded by a round, optically empty space or halo, giving cell the appearance of a “fried egg”, reflecting artifact of fixation 3. Three to five oligodendroglial cells in the gray matter may surround the cell body of the neuron, designated as BENIGN SATELITOSIS |
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Glial cytoplasmic inclusions are seen in association with…?
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MULTIPLE SYSTEM ATROPHY
-- sporadic olivopontocerebellar atrophy -- striatonigral degeneration -- Shy-Dragner syndrome (familial) Inclusions: -- minute silver-positive intracytoplasmic structures -- contain protein alpha-synuclein |
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What is microglia?
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Third element of the nervous system (combined w/ oligodendroglial cell)
-- mesodermal origin -- fixed CNS precursor of the macrophage system -- activated by injury |
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Characteristics of microglial cell?
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Small, spindled or cigar-shaped nucleus
-- cytoplasm is not visible w/ H&E stain -- small amt of cytoplasm w/ few processes, reflecting specialized fxn as a fixed macrophage precursor -- when activated by injury, removes damaged CNS, w/ ultimate formation of a cavity or hole as an endstage, lytic lesion -- acts as “garbage man” of the nervous system When activated in response to injury, spindled microglia become prominent and are referred to as “rod cells” |
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Scar formation in the CNS?
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Rare in the nervous system – heals by cavitation – terminal phase of the healing process
Present in wall of abscess cavity and also characterizes organization of subdural hematomas |
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What is a glial nodule?
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Focal constellation of neuronal ingestion that occurs as mature macrophages congregate around injured tissue, especially around neurons
-- particularly in reference to VIRAL diseases of CNS |
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What is neuronophagia?
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Focal constellation of neuronal ingestion that occurs as mature macrophages congregate around injured tissue, especially around neurons
-- refers to NON-viral forms of CNS injury |
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When known cause of injury (viral vs. nonviral) is absent in CNS, the terms ________ and _________ are synonymous.
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Glial nodule and neuronophagia
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Name for tumor of microglial origin?
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No current tumor of microglial origin
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What are ependymal cells?
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Single layer of cuboidal cells which line the ventricular surfaces
-- neuroectodermal origin -- probably represent modified astrocytes, based on presence of GFAP(+) cytoplasmic processes -- contain cilia during fetal period, although the cilia disappear after birth, leaving only basal body, or BLEPHAROPLAST of the cilia as ultrastructural remnant |
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What occurs when there is an infection of the ventricular surface?
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May denude scattered foci of ependymal cells, which are replaced by reactive astrocytes, resulting in formation of minute granular structures visible to the unaided eye as GRANULAR EPENDYMITIS
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What happens to damaged ependymal cells?
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Do NOT regenerate
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How are the ependymal cells normally characterized?
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Characterized by presence of tight cytoplasmic fxns which are impervious to influx of CSF into adjacent CNS parenchyma, reflecting a normal barrier fxn
-- In certain instances of hydrocephalus, tight fxns may be opened, w/ resultatnt insudation of CSF into adjacent parenchyma, designated as hydrocephalic edema |
