Traumatic Brain injury Flashcards
What is traumatic brain injury
Injury to the brain caused by trauma to the head
- not congenital or degenerative in nature but caused by external physical force
What is the healthy frontal lobe associated with
- speech
- problem-solving
- concentration
What is the healthy parietal lobe associated with
- sensation of pain
- temperature
- touch
What is the healthy occipital lobe associated with
healthy vision
What is the healthy temporal lobe associated with
- memory
- organization
What is the healthy cerebellum associated with
- balance
- coordination
What is the healthy brain stem associated with
- breathing
- steady heart rate
What would a TBI in the frontal lobe result in
- language difficulty
- lack of focus
- irritability
What would a TBI in the temporal lobe result in
- problems with long and short term memory
What would a TBI in the occipital lobe result in
- blind spots
- blurred vision
What would a TBI in the parietal lobe result in
- spatial misperception
- difficulty reading
What would a TBI in the cerebellum result in
- difficulty walking
- slurred speech
What would a TBI in the brain stem result in
- changes in breath
- difficulty swallowing
What are the two types of traumatic head injury
- Open-head injury (penetrating injury, including fractures and bone segments)
- Closed head injury (blunt injury, including stroke)
What does the severity of open head injury depend on
areas affected
When is open head injury fatal
- when there is damage to both hemispheres, ventricles and multiple lobes
Who is more at risk for open heady injury
- children and infants
What is the process of closed head injury
- consists of a coup and contra-coup
- first point of contact= coup
What does a coup and a contra-coup usually result in
- subdural haematoma due to close head injury
What is a subdural haematoma
- bleeding under dura matter
Name the three types of axonal injury
- Twisted axon pulled away at synapse
- Torn axon
- Broken axon
What secondary damage can a closed head injury result in
○ Immediate leak of neurotransmitters
○ Lack of oxygen and glucose to the brain
○ Leads to inflammation
Name the outcomes of closed head brain injury
- Bleeding (subdural haematoma)
- Tearing (tearing and twisting of brain in the skull)
- Sheering (secondary damage)
Describe the pathology of the BBB in TBI
- secondary damage caused by severe closed head injury
- disruption of BBB
- cascade of neurochemical events
- potassium and sodium
- chloride
- glutamate
- Swelling and inflammation from tissue damage
- increases pressure on the brain in turn leading to more damage
What are the treatment options available for a leaky brain
- no known drug can stop the leak of neurotransmitter or the swelling of the brain
- chilling of the brain is the only known treatment that works
Why does chilling of the brain work as an efficient treatment for swelling and inflammation
- Excitotoxicity is temperature sensitive
- high temperatures are required as a catalyst for neurotransmitters to cascade
- a lower temperature prevents the aforementioned from occuring
What diagnostic imaging techniques can be used to scan for TBI
- CT scan
- X-ray
- PET scan
- MRI (functional or resting state)
- Diffusion tensor imaging
- EEG
What is secondary impact syndrome
- life threatening
- result of back-to-back concussions
- results in a loss of autoregulation of blood supply:
- vascular engoregement
- increased intracranial pressure
- rapid brain stem failure
What is Dementia Pugilistica
- punch drunk syndrome
- boxing dementia
- similar to CTE
- associated with memory loss and slurred speech
What is Chronic Traumatic Encephalopathy
- CTE
- Evidence that there’s a link between traumatic brain injury and neurodegenerative diseases
- higher risk for people with Apoe4 gene
- Can be diagnosed by tau protein aggregation
- Also found in hippocampus (classic area for AD)
- Repeated hits to the head leads to aggregation of Tau
What do MRI-CT scans of brain injury tend to show
- Change in enlarged vesicles
- Gyri becomes more prominent
- Grooves shrink
- Loss of brain matter
What can affect the rate of cognitive decline
- TBI can shift the timeline to get dementia towards a younger age
- TBI in combination with CTE can shift it even further
What does the neurotoxic cascade following TBI consist of
- Excitotoxicity
- Ischaemia
- BBB disruption
- Cerebral odeoma
- Energy failure
- Cell death cascade
What types of glia are a part of the CNS
- Microglia
- Oligodendrocytes
- Astrocytes
- Ependymal cells
What role do microglia play in the CNS
- clean up debris and pathogens via phagocytosis
What role do ependymal cells play in the CNS
- line the ventricles and central canal
- assist in the production, circulation and maintenance of CSF
What role do astrocytes play in the CNS
- form scar tissue
- provide structural support
- maintain BBB
- regulate homeostasis in the brain
What role do oligodendrocytes play in the CNS
- myelinate CNS axons
- provide structural framework
What types of glia are a part of the PNS
- Schwann cells
- Satellite cells
What role do satellite cells play in the PNS
- surround neurons in the ganglia
- regulate O2, CO2, nutrients an neurotransmitter levels around neurons in ganglia
What role do schwann cells play in the PNS
- myelinate peripheral axons
- part of repair process after injury
What are the different shapes of microglia
- Bipolar/rod
- Amoeboid
- Ramified
What can move through the BBB
- oxygen
- water
- lipid soluble proteins
What surrounds the BBB
pericytes
What modulates the transfer of nutrients b/w glial cells and the membrane
pericytes
What is the gliovascular complex
the BBB and the astrocytes surrounding it
What happens to the gliovascular complex in TBI
- entire complex is disrupted
- endothelial cells are ruptured
- greater exposed surface area that allows more materials to exchange
- disruption of pathways of transport across the BBB allows the flow of neurotransmitters in the wrong direction and may contribute to excitotoxicity
What are the pathways across the BBB
- Paracellular aqueous pathway (water soluble proteins)
- Transcellular lipophilic pathway (lipid soluble agents)
- Transport proteins (glucose, amino acids)
- Receptor mediated (insulin)
- Adaptive transcytosis (albumin and other plasma proteins)
How is the structure of the brain affected in TBI
- Bleeding, tearing, sheering
What are the stages of TBI
- Mechanical damage
- Inflammation and angiogenesis
- Glial scar formation
- Structural tissue regeneration
How does TBI progress
- Acute injury causes secondary damage to the BBB leading to tearing, bleeding and sheering
- BBB leakage allows monocytes in the blood stream to migrate to the site of injury within the brain parenchyma and trigger the activation of microglia
Explain the role of mircoglia during inflammatory events
- First line of defence in the CNS
- constantly scan the CNS and are very sensitive to changes in the environment
- Under normal conditions, microglia exist in a resting ramified state wherein they function as debris-collectors for cellular debris and apoptotic cell via phagocytosis
- Activated microglia can polarize into M1 (pro-inflammatory) or M2 (anti-inflammatory) state depending on the nature of the inflammatory stimulus
Name some inflammatory events that can activate microglia
- Neuronal damage
- invasion by infectious agents
- presence of pathogenic proteins
Describe the polarization states of microglia and their relationship
- M1 state: pro-inflammatory, classical activation
- respond to injury or infection
- produce oxidative metabolites and proinflammatory cyokines and chemokines
- induce infiltration of peripheral leukocytes to clear up the site of injury or infection
- M2 state: anti-inflammatory, neuroprotective, alternative activation
- microglia antagonize the M1 pro-inflammatory responses
- secrete anti-inflammatory cytokines
- facilitate phagocytosis of cell debris
- induce reconstruction of the ECM and tissue repair
- also produce neurotrophic factors to support neuronal cell health and survival
Describe the timeline of polarization of microglia
- After an insult to the brain, monocytes, microglia, and rod microglia are activated
- Monocytes migrate to lesioned areas, whereas gray matter microglia are less likely to displace
- Microglia change morphology in a time-dependent fashion, sprouting new ramifications soon after injury, and then withdrawing branches to develop an ameboid phenotype
- In the very early phases after injury, microglia have a M1 phenotype, then, with the recruitment of macrophages, both myeloid populations upregulate M2 markers
- The peak of M2 marker expression soon vanishes and is followed by upregulation of M1 markers that lasts longer
What process occurs with monocytes after TBI?
- Adhesion
- Infiltration from blood
- Migration
- Proliferation
What process occurs with microglia after TBI?
- Limited migration
- Damage sensing profile changes branch outgrowth
- Reactive markers branch withdrawal
- Phagocytosis, phagoptosis, ameboid
Discuss the use of xray in TBI imaging
- for skull bone damage
Discuss the use of CT in TBI imaging
- bleeding in the skull area
Discuss the use of MRI in TBI imaging
- can identify build up of fluid in brain
- can identify skull fractures
Discuss the use of EEG in TBI imaging
- for irregular electrical activity eg seizures
Discuss the use of PET in TBI imaging
- Expensive
- Says about the same as an MRI
- Useful if you’re looking for a specific protein
Discuss the use of diffusor tensor imaging in TBI imaging
- Visualises damage to the brain by isolating white matter tracts
- Massive equipment which needs a lot of room and is expensive to buy
What is the proposed mechanism for excitotoxicity from leaky BBB in TBI
- Disrupted endothelial membrane due to injury from TBI
- Immune cell circulate in the blood stream and brain and activate microglia and astrocytes
- Activated astrocytes secrete S100
- Activated microglia secrete and get activated by:
glutamate
Arachadonic acid
quinolonic acid
pro-inflammatory cytokines (IL-1B, TNFa, IL2, IL6) - This leads to free radical generation of lipid peroxidation and peroxynitrite)
- This leads to mitochondrial dysfunction
- Mitochondrial dysfunction leads to accelearated excitotoxicity and synaptic dysfunction
- ultimately leads to excitotoxicity
Which markers give indication of microglia activity?
TSPO
What is the marker for astrocytes?
GFAP
What are the main NEURODEGENERATIVE-ASSOCIATED GENES specifically expressed in microglia?
- APOE4
- TREM2
- BDNF
What is astrogliosis and how does it occur
- Astrogliosis is the adjustment of astrocytes to insult/injury in the brain
- Insult to epithelial tissue causes the release of cytokines like IL1B, TNFa, IL2 and ROS
- This activates resting astrocytes
- Reactive astrocytes induce recruitment and proliferation of other astrocytes as they migrate to the site of injury to form an astroglial scar
What is the evidence for microglial priming in TBI
- microglia are said to be primed for activation after TBI, making individuals prone to secondary impact syndrome
- Already in active state and producing cytokines
- If another insult occurs, microglia becomes even more active due to priming
- Blood monocytes also enter brain after TBI
- Secrete similar things to microglia
- Overall increased response and inflammation
What are the hallmarks of astrocyte reactivity
- Increased homeostatic and trophic functions
- Secretory activity
- Proliferation
- Migration
- Glial scar formation
What are the models available for TBI
Diffuse injury - Blast injury - Weight drop injury Focal injury - Fluid percussion - Controlled cortical impact injury model - Weight drop energy
What is a glial scar formed by
- Migration of myelin-associated inhibitors, astrocytes, oligodendrocytes, oligodendrocyte precursors, and microglia
Why does scar formation inhibit axon regeneration?
NG2 GLIA (polydendrocytes) may inhibit axon regeneration by:
- expression of inhibitroy NG2 proteoglycan
- formation of synaptic contacts
What is the controlled cortical impact injury model and what are its advantages
- easily reproducible
- mimics:
concussion
BBB rupture
axonal injury
What is the weight drop injury model and what are its advantages
Two models
- one with a protective disk on top so when weight is dropped there are no skull fractures, associated with diffuse injury
- one with an unprotected skull so weight is dropped to one side of the skull, associated with diffuse injury
What is the fluid percussion injury model and what are its advantages
- mimics TBI without skull fracture
- pathophysiological features like:
- intracranial bleeding
- brain swelling
What is the blast injury model and what are its advantages
- military personnel experience TBI without skull fractures
- this model is ideal to study how blast waves induce brain injuries