Pathology of the Nervous System Flashcards
What are neurons?
long-lived cells; organized into layers and clusters within gray matter
What are astrocytes?
supportive cells that regulate the microenvironment and respond to CNS injury; they are part of the blood brain barrier
What do oligodendrocytes do?
provide myelin sheaths around axons, surround neurons, and help regulate the microenvironment
What are microglia?
CNS phagocytes
What are microglia derived from?
monocytes
Where are ependymal cells located and what do they do?
they line ventricles and help produce CSF
What are the layers of the meninges?
dura mater, arachnoid, and pia mater
Which layer of the meninges is the vascular layer?
the arachnoid
Which layer of the meninges is the inner layer bonded to the neurophil?
pia mater
Which layer of the meninges is the tough fibrous covering?
the dura mater
What is the CNS made up of?
blood vessels, gray matter, and white matter
Where do the blood vessels penetrate the brain and the cord through?
the arachnoid
What are the blood vessels of the CNS surrounded by?
potential space (Virchow-robin space)
What is the blood brain barrier made up of?
capillary endothelium, basement membrane, and astrocytes
What is the root word for gray matter?
polio
What groups are the neuronal cell bodies of gray matter organized into?
layers, nuclei, and ventral and dorsal horns
what are the layers of the gray matter?
serebral and cerebella corticies
What are the nuclei in gray matter?
medulla and brain stem
What is the root word for white matter?
leuko
What is the white matter composed of?
myelinated axon tracks
Where are the upper motor neurons located?
with in the brain - they are cell bodies
What do the axons of the upper motor neurons make up?
descending motor tracts in the cord
What is the function of the upper motor neurons?
they initiate and regulate motor stimuli to lower motor neurons
What is the result of upper motor neuron injury?
spastic paresis/paralysis due to loss of inhibatory stimuli
Where are the lower motor neurons located?
within the ventral horns of the spinal cord and motor nuclei of cranial nerves of the brain
What do the axons of the lower motor neurons make up?
ventral nerve roots; extend to motor-end plays at the neuromuscular junction
Are the upper motor neurons or the lower motor neurons part of the reflex arc?
the lower motor neurons
What does lower motor neuron injury cause?
flaccid paresis/paralysis
What is the peripheral nervous system made up of?
neurons, axons, and the reflex arc
What neurons are part of the peripheral nervous system?
lower motor neurons, sensory neurons, and peripheral ganglia and plexuses
Where in the peripheral nervous system are sensory neurons located?
in the dorsal root ganglia
What system are the peripheral ganglia and plexuses a part of?
the autonomic nervous system
What axons are part of the peripheral nervous system?
sensory and motor
What do the sensory axons synapse with?
ascending sensory tracts in the dorsal and lateral funiculi; cranial nerves
What do the motor axons of the peripheral nervous system extend to?
motor-end plats or autonomic ganglia
What are the spinal and cranial nerves made up of?
a mixture of axons from sensory and motor neurons
What do schwann cells do?
produce myelin around each axon
What are the layers of fibrous tissue in the peripheral nervous system?
endoneurium, perineurium, and epineurium
Which nervous system does Wallerian degeneration happen in?
peripheral
What is the pathogenesis of Wallerian (axonal) degeneration?
- axon proximal to injury swells and dies back 2. axon distal to injury deteriorates 3. debris is cleaned up by macrophages
What lesinos are associated with Wallerian degeneration?
spheroids + dilated axon sheaths + macrophages
If the axon sheath is intact in Wallerian degeneration, what happens?
the myelinated axon regrows
What s central chromatolysis?
sublethal change in neuronal morphology leading to peripheral dispersal of Nissl substance
What is demyelination?
specific loss of myelin
what is neural fibrosis and atrophy secondary to?
chronic or disruptive injury
What exudate is associated with neuritis/ganglioneuritis/polyradiculoneuritis?
lymphoplasmocytic to pyogranulomatous exudate
What causes neuritis/ganglioneuritis/polyradiculoneuritis?
autoimmune mechanisms (polyneuritis equi) ascending infectious agents (rabies, listeria monocytogenes)
What nerve does ganglioneuritis from rabies cause?
inflammation to the trigeminal ganglion
What is a neuroma?
a non-neoplastic mass due to abnormal regrowth of a nerve
What are peripheral nerve sheath tumors derived from?
Schwann cells or fibroblasts
What are peripheral nerve sheath tumors common in?
subcutis and brachial plexus
Are peripheral nerve sheath tumors benign or malignant?
they can be both
What can malformations in the CNS be due to?
genetic defects or injury to part of the brain/cord during development (in utero or toxins)
What are some examples of CNS malformations?
hydrocephalous, hydranencephaly, cerebellar hypoplasia, and Dander-Walker malformation
What is hydrocephalus (generally)?
dilation of the ventricular system of the brain associated with accumulation of CSF
What are the types of hydrocephalus?
internal and external
Which type of hydrocephalous is the most common?
internal hydrocephalous
What is internal hydrocephalus due to?
obstruction of the ventricular system
What is external hydrocephalus due to?
failure to absorb CSF by arachnoid villi
What is hydranencephaly?
a CSF-filled cavity replacing the cerebral hemispheres
What causes hydranencephaly?
destructive lesion in the brain
What is cerebellar hypoplasia?
a developmental failure of the cerebellum to attain the appropriate size and structure
What lesions are associated with cerebellar hypoplasia?
small cerebellum and lack and/or disarray of purkinje neurons
What clinical signs are associated with cerebellar hypoplasia?
hypermetria, dysmetria, ataxia, and intention tremors
What causes cerebellar hypoplasia?
in utero viral infection of external granular layer of cerebellum and inherited in some species
What are some examples of in utero infections that can cause cerebellar hypoplasia?
feline parvovirs and bovine viral diarrhea virus
What is axonal degeneration similar to?
Wallerian degeneration in the PNS
Describe axonal degeneration.
little to no axonal regeneration; lack of a basement membrane
What are the types of demyelination?
primary and secondary
What is primary demyelination?
specific injury to oligodendrocytes
What is secondary demyelination?
general injury to axon and myelin sheath
What is central chromatolysis?
early injury in the CNS; dispersal of Nissl substance
What is hydropic degeneration?
swelling due to impaired ion pumps
What is apoptosis in the CNS?
single cell ‘programmed death’; no inflammation
What is CNS necrosis?
1 or more cells die in response to injury; elicits inflammation
What is CNS spongiform change due to?
prion diseases
What are intracellular accumulations in the CNS due to?
enzyme deficiency storage diseases
What morphological changes are associated with neuronal necrosis?
shrinken, hypereosinophilic, +/- pyknotic nucleus, adjacent activated astrocytes, satellitosis with oligodendrocytes; red=dead
What can cause neuronal necrosis?
hypoxia/ischemia, toxins, excitotoxins, and viruses
What do excitotoxins do?
stimulate neurons to death
What is the outcome of neuronal necrosis?
neurons that are lost are not typically replaced
What are TSEs associated with?
neuronal spongiform change
What does TSE stand for?
transmissible spongiform encephalopathies
What are some examples of TSEs?
scrapie (sheep), BSE (cattle), Chronic wasting disease (elk, deer), Cruetzfeldt-Jakob disease and Kuru (humans)
What causes neuronal spongiform change?
protease resistant prion protein
What is the pathogenesis of neuronal spongiform change?
normal cellular prion protein becomes mis-folded and they lack nucleic acid; replicate by converting PrPc into PrPsc
How are infectous causes of neuronal spongiform change transmitted?
orally then they replicate in lymphoid tissue, get to the CNS by leukocyte traffic or retrograde migration up the cranial nerves
What regions of the brain are affected by neuronal spongiform change?
medulla oblongata at obex, brain stem nuclei, cerebellum, and retina
What storage diseases are associated with galactocerebrosidase?
galactocerebrosidosis
What storage diseases are associated with beta mannosidase?
beta mannosidosis
What happens in storage disease?
There is an accumulation of substrate leading to enlarged neurons with intracellular accumulation
What are the causes of storage disease?
inherited or acquired
What are some causes of parenchymal swelling?
cytotoxic edema and increased vascular permeability
What is cytotoxic edema?
hydropic degeneration
What is increased vascular permeability associated with?
inflammation
What is the result of parenchymal swelling?
due to the closed space there is herniation which leads to ischemia and necrosis
Where does CNS hemmorhage typically occur?
in the leptomeninges (subdural hemorrhage) or parenchyma
What is the neuropil?
the parenchyma
Hemmorhage is toxic to the ______.
neuropil
What is hematomyelia?
progressive hemorrhage and necrosis that spreads; typically occurs in the spinal cord
What are the causes of hemorrhage in the spinal cord?
trauma, vasculitis, or coagulopathy
What exudate types are associated with inflammation in the CNS?
serofibrious, purulemt, lymphocytic/lymphoplasmacytic, and pyogranulomatous and granulomatous
Where does inflammation in the CNS occur?
leptomeninges, Virchow-robin spaces/perivascular, neuropil, and ventricles
What is enceohalonalacia?
necrosis of the brain
What is myelomalacia?
necrosis of the spinal cord
What is polioencephalomalacia?
necrosis of gray matter in the brain
What is leukopolioencephalomalacia?
necrosis of white matter in the brain
What is poliomyelomalacia?
necrosis of gray matter in the spinal cord
What is leukomyelomalacia?
necrosis of white matter in the spinal cord
Necrosis causes what to the brain tissue?
liquefaction
What is liquefied brain tissue cleaned up by?
gitter cells causing a hole
Where in the CNS does fibrosis occur?
only in the leptomeninges
What do microglia and macrophages become in fibrosis?
gitter cell
What are gitter cells?
brain phagocytes
What is gliosis?
basically the analog of fibrosis but in the parenchyma as the result of astrocyte proliferation
What are activated astrocytes?
hypertrophied astrocytes due to sublethal injury
What are fibrous astrocytes?
elongated astrocytes that attempt to fill inlost neuropils
What is satellitosis?
a form of astrocytosis that occurs around neurons
What are gemistocytic astrocytes?
hypertrophied astrocytes due to proliferation of gliofibrulary acidic protein (intermediate filament of astrocytes)
What is myelitis?
inflammation of the spinal cord
What is poliomyelitis?
inflammation of the gray matter of the spinal cord
What is leukomyelitis?
inflammation of the white matter of the spinal cord
What is myelomalacia due to?
inflammation or ischemia
What is ischemic myelopathy secondary to?
intervertebral disk disease or IV disk cartilage emboli
What neoplasmas are associated with the CNS?
neuroblastomas/medulloblastomas, astrocytomas, oligodendroglioma, ependymoma, meningioma, lymphosarcoma
