Neurology Response to Injury Flashcards
“Neuro-”
lesion of peripheral nerves
“Myello-”
Lesoin of spinal cord
Leuko-
white matter
Polio-
grey matter
Leptomeninges
arachnoid and pia mater
Pachymeninges
dura mater
-malacia
degeneration, liquefaction, softening of neural tissues
What are the normal layers of the meninges?
- Dura mater
- Subdural space
- Arachnoid mater
- Subarachnoid space
- Pia mater
What is Grey Matter?
- Darker tissue of the brain and spnal cord
- Comprising nerve cell bodies and dendrites
What is White Matter
- Paler tissue of the brain and spinal cord
- Composed mainly myelinated nerve fibers
What are the different functions of the 4 types of neural cells?
- Neurons - nervous function
- Astrocytes - structure, BBB, immune response
- Oligodendrocytes - myelin
- Microglial - resident immune/phagocytic cells
What is the structure of Neurons?
- Pyramidal to rhomboidal shaped
- Large nucleus with prominent nucleolus
- Cytoplasm contains Nissl substance (rER)
- Axon - axoplasm, few organelles, myelinated
- Myelin - Oligodendrocytes or Schwann cells
- Cannot regenerate
Where were the different types of neural cells derived from?
- Neuron - neural crest
- Astrocytes - neural crest
- Oligodendroglia - neural crest
- Microglia - Bone marrow- derived monocytes
What is Neuropil?
- Eosinophilic fibrillar material between cell nuclei composed of the cell processes of neurons and glia
What are the functions of astrocytes?
- Structure - assist to maintain brain structure
- mesenchymal cells of the CNS
- Homeostasis - intracellular link between capillaries and brain cells (BBB)
- Immune regulation - produce cytokines & chemokines, T-cell activation, microglial cell activation
What are the functions of Oligodendrocytes?
- Make and maintain myelin
- Myelinate many axons
What is the function of schwann cells?
- Provide myelin for peripheral nerves
- One schwann cell myelinates a portion of one axon
What is the function of Microglial cells?
- Resident phagocytic cell
- Analogous to Kupffer cells (Liver), alveolar macrophages (lung) and Langerhans cells (epidermis)
What does the Microciculation of the brain look like?
- Capillaries
- Endothelial cells are connected by tight junctions
- Small capillaries lack a pericapillary space
- Astrocytic processes form the BBB
- Larger Blood Vessels
- Perivascular space is only distinct around larger vessels and is contiguous with the surface leptomeningies
- “Virchow-Robbins Space”
- Inflammatory cells in this space are called perivascular cuffs
- Perivascular space is only distinct around larger vessels and is contiguous with the surface leptomeningies
What is the neural cell response to injury?
- Very small energy stores - depend heavily on intact blood supply
- Virtually no capacity to regenerate
- CNS nerve fibers cut = paralysis
- PNS = possible regeneration
- Healing through astrocytes NOT fibrosis
- Very little resistance to even relatively non-pathogenic organisms
- No lymphatics, lymphoid tissue
What is Reversible cell injury?
- Results in dispersion of Nissl substance (rER) and cell welling
- Loss of obvious Nissl substance = “chromatolysis”
What happens to ischemic neurons?
- Shrunken, red, angular, pyknotic nuclei
- Neurons are MOST susceptible to ischemic injury
What causes dead neurons?
- Necrosis:
- Ischemia
- Viral infections (some cause inclusions)
- TOxins
- Prions - large cytoplasmic vacuoles
- Metabolic disease - lysosomal storage disease
- Apoptosis:
- Inherited disease/congenital defects
- Viral infections
- Toxins
What causes intranuclear inclusion bodies?
- Herpes Virus
- Adenovirus
- Posvirus
- Rabies - “Negri bodies”
What is a lysosomal storage disease?
- neurons have markedly expanded cytoplasm due to accumulation of ‘waste’ in lysosomes
- Most common in cats is ‘Globoid cell leukodystrophy’ “Krabbe’s Disease”
What toxin causes lysosomal storage disease?
- Swainsonine (Locoweed toxicosis)
- Signs:
- Weight loss
- severe depression
- lethargy
- ataxia
- incoordination
- hypermetric gait
What causes Neuronal vacuolization?
- Spongiform encephalopathies
What is “Neuronophagia”
- Macrophages and other inflammatory cells surround (satellitosis) and phagocytose/digest dead neurons
What is Wallerian Degeneration?
- Spinal cord compression resulting in axonal degeneration
- Macrophages infiltrate and phagocytize axonal debris and degenerated myelin - hallmark
- Long term effects depend on:
- Severity of injury
- Intact or damaged endoneural tube surrounding axon
- Integrity of oligodendroglia
What are the Axonal changes as a response to injury?
- Wallerian degeneration
- severing or direct axonal damage
- Regeneration
- PNS>>>>CNS
- Demyelination
- Primary - loss of Oligos or Schwann cells
- Secondary - death of the neuron
What are some causes of Primary demyelination?
- Canine Distemper Virus (CDV)
- Caprine Arthritis-Encephalitis Virus (CAE)
- Globoid cell leukodystrophy
What does Primary Demyelination look like grossly?
- Clear spaces in the cerebellar white matter
Where and why can CDV form inclusion bodies ?
- In the nucleus AND Cytoplasm
- Because its and RNA virus
What are the Astrocytes responses to injury?
- Cell Death:
- Necrosis - not as susceptible to ischemic injury as neurons
- Apoptosis
- Nonlethal reactions - function to fill in or wall off areas of necrosis
- small area = proliferation & “glial scar” (focal gliosis)
- Large area = cavitation in brain tissue (Lacunar infarcts)
What is the difference between an Astrocyte and a Fibroblast?
- Astrocytes:
- Mesenchymal cell of CNS
- Maintain structure
- Maintain BBB
- Cannot produce fibrosis in the neuropil
- Lay down collagen only in meninges
- Fibroblasts:
- Mesenchymal cell in body
- Maintain structure
- Lay down collagen as part of healing
What are the synonyms for the formation of glial scars by astrocytes?
- hyperplasia of astrocytes
- astrocytosis
- astrogliosis
- focal gliosis
- glial nodule
- formation of “glial scars”
