Pathology: Reactions of the nervous system to injury Flashcards
What are the 3 layers of the meninges?
Dura Mater
Arachnoid
Pia Mater
In the brain, which of the white matter or grey matter is central and peripheral?
White matter = Central
Grey matter = Peripheral
What cells predominate in the white matter of the brain?
- well-myelinated axons
- oligodendrocytes (support and insulation)
- astrocytes (maintain brain homeostasis and metabolism)
What cells predominate in the grey matter of the brain?
- cell bodies of neurons
- dendrites
- glial cell processes (maintain homeostasis, support + protection)
to a lesser extent: oligodendrocytes, astrocytes and microglia
What structures are in the dorsal funiculus of the spinal cord?
ascending sensory axons
What structures are in the ventral funiculus of the spinal cord?
descending motor axons
What structures are in the lateral funiculus of the spinal cord?
mix of both ascending and descending axons
What are the major gross lesion patterns of the nervous system with examples?
- Deviation from normal anatomy: malformation, brain swelling, atrophy
- Space-occupying masses: tumour, abscess or granuloma
- Haemorrhage: Contusion/ Trauma, Circulation problem, Infection, Deficiency or Toxin
- Malacia (abnormal softening of tissue): Infarction, Deficiency or Toxin
- Selective white matter changes: dysmyelination, leukodystrophy, demyelination
List the following cells in order of most susceptible to hypoxic/ anoxic injury to least
blood vessels, oligodendrocytes, neurons, astrocytes, microglia
neurons > oligodendrocytes > astrocytes > microglia > blood vessels
Why are neurons the MOST susceptible to hypoxia/ anoxic injury?
Neurons have small energy stores which are entirely dependent on oxygen and glucose
Can neurons regenerate in the CNS?
Neurons cannot regenerate in the CNS, nerve fibres may have small regeneration capability
In the rest of the body the healing process is dependent on fibroblasts creating a fibrous mesh (scar), how does the CNS heal?
The CNS only has a few number of fibroblasts, which are located in the meninges. Healing of the CNS is mainly through proliferation of astrocyte processes, which have a very poor capsule and can break down easily
What makes up the Blood Brain Barrier?
The BBB is formed by tight junctions of endothelial cells, aided by basement membrane and the end feet of astrocytes
Which cells of the CNS are of Ectodermal origin?
Neurons
Astrocytes
Oligodendrocytes
Ependymal Cells
note: all of these cells are of ectedermal origin and are sensitive to hypoxia
Which cells of the CNS are of Mesodermal origin?
Microglia (resident macrophages)
Vascular Endothelium
note: all of these cells are of mesodermal origin and are more resistant to hypoxia
What is Excitotoxicity Injury?
Excitotoxicity Injury is when an excessive and sustained release of an excitatory neurotransmitter (commonly Glutamate), paired with the decreased removal of Glutamate by astrocytes due to ischemia, hypoxia or hypoglycemia causes Glutamate to bind to the neuronal membrane, causing an influx of Calcium into the neuron and the activation of proteolytic enzymes, and creation of Reactive Oxygen Species which leads to oxidative damage
Describe ‘Chromatolysis’
Chromatolysis is the swelling of the cell body and the dissolution of Nissl granules with margination of the neuron nucleus
- It is a Degenerative but reversible change
- Non-specific causes: injury to axons, overstimulation/ deficiencies
- Is seen in Lower Motor Neuron Diseases: dysautonomia (grass sickness in horses) and copper deficiency in sheep
Describe ‘Ischaemic Necrosis’/ ‘Acidophilia’
Ischaemic Necrosis is when cells are shrunken, angular and acidophilic due to ischemia, hypoxia, hypoglycemia, thiamine deficiency or seizures
- It is an acute degenerative and permanent change
- This particular change can only be detected on histopathology 6-8 hours following the triggering injury (important for PM)
Describe ‘Vacuolar Degeneration’
Vacuolar Degeneration is the formation of nonlipid vacuoles in cytoplasm, most frequently due to edema or Storage diseases
- Some vacuoles can be found incidentally in certain brain regions
- Large neuronal vacuoles in high numbers within the Medulla and Midbrain are pathognomonic for Scrapie in Sheep and Goats, and BSE in Cattle
What is suggestive of Inclusion bodies within the neurons of the CNS?
Viral Infection:
- Rabies – Negri bodies (eosinophilic cytoplasmic)
- Herpes virus (intranuclear inclusions)
- Canine distemper virus (intranuclear, intracytoplasmic)
- Borna disease (Joest-Degen inclusion bodies)
Non-Viral Inclusions:
- Pigments associated with aging (incidental finding)
- Storage Diseases
Describe ‘Neuronophagia’
Neuronophagia is Neuronal necrosis with neurophagia, suggestive of many viral infections
- the death of a neuron provokes the gathering of phagocytes around the cell body and the removal of the debris
The Myelin Sheath is made by what cells in the CNS and in the PNS?
CNS: Oligodendrocytes (regenerates poorly)
PNS: Schwann Cells (better regeneration)
What is Anterograde Axoplasmic Flow?
A directional flow from cell body to synapse within a neuron
- Slow (1mm/day): for growth and maintenance
- Fast (1000mm/day) for synaptic function
note: same direction used by the Herpes Simplex Virus
What is Retrodrage Axoplasmic Flow?
A directional flow from axon termini to cell body within a neuron
- directional flow used by returning synaptic vesicles and other materials
note: used by infectious agents (listeria + rabies)
used by toxins (tetanus)
