Introduction to Clinical Neuroscience Flashcards
Function of CSF
- Conduit to removing toxins
- Cushions brain from impact
What supplies the brain with blood?
Arterial system supplies brain with blood which goes deep into the brain matter
What is the white matter?
Astrocytes, and glia are brain matter beneath this
What do dendrities receive and subsequent action?
- Receive signals from other neurons
- Get processed in the cell body
- Transmitted through axon via dendrites
- Dendites receive signals
- Axons transmits the processed signal
How many cells are dendrities connected to?
Approx. 10,000 others
Dendrities are not born static. What does this mean?
Over the first few weeks of life, dendrites can change, plasticity of the brain.
When there are physical changes in the brain what does this relate to?
This relates to learning new skills
What is artificial intelligence based on?
Based on the structure of the cell body turned into an artificial neural network
What is grey matter used for?
It is used for sensation i.e. control of our hands
What is a stroke of the brain?
Loss of motor function as brain matter is damaged
What can frontal lobe damage cause?
- Personality changes
- > Fitful
- > Irreverent
- > Impatient
What happens if there is damage to Broca’s area?
Affects speech
Post-mortem pathology
- Limited as can only be performed after death
- Can take tissue for analysis of genes/proteins
- Can look at brain structure to understand disease processes to develop treatments
- Need diagnostic tools for living patients = medical imaging
What is a glioblastoma?
- Malignant, highly infiltrated brain tumour
- Tumour grows from one hemisphere to the other
- Difficult to treat as grows very fast
- Highly infiltrative so difficult to remove without damaging the function of the brain
What is a haemorrhagic stroke?
- Localised damage
- Blood vessel is blocked so region of tissue that is supposed to be supplied by blocked blood vessel dies.
What is hippocampal sclerosis?
- Hippocampus smaller on one side
- Can cause seizures/alzheimer’s/dementia
- Part of the brain where Alzheimer’s starts
How do X-rays work?
- They pass through air/soft tissue but not through bone.
- X-ray absorbed by bone but not by tissue as strongly - can therefore look at bony structures.
Can X-rays be used on the brain?
The brain is surrounded by skull so it is not helpful for looking at the brain.
When is the use of X-rays useful?
It is useful in trauma: penetrating wounds i.e. bullet wounds
How do X-rays work?
- X-ray tube rotates around the patient
- Detected on other side
- Measure attenuation at every angle
- > Bright intensity = strong attenuation
- Dark intensity = x-rays can pass through easily.
What is attenuation?
Reduction of force
When are X-rays used?
- To show detailed images of internal organs and therefore can detect cancers and minor fractures
- Can turn “line signals” into 2D images
- Can be used to help understand blood flow
- Grey and white matter cannot be seen even though there is a slight difference in intensity between both matters but subtle differences in the brain are lost and cannot be seen.
What is MRI?
It uses chemical technique to understand the brain structure. The signal that comes from tissue water to generate signals.
What generates the MRI?
The magnets within us generate the MRI - T2 weighted MRI
How does an MRI work?
- Fluid shows up bright (so CSF can be seen)
- Convolutions of cortex can be seen
- Signal comes from water in the brain to form this image.
- Hydrogen atoms have proton in the nucleus which is positively charged so generates a signal in MRI
- Radio frequency interacts with protons and this generates signals from within the tissue itself
- Picked up by radio frequency coils and turned into an image
What happens if there is more water in an MRI?
There is a stronger signal because the signal from water causes structural changes in the tissues and alters signal intensity in image so pathology can be seen.
What is T2 weighted MRI?
T2 reflects the length of time it takes for the MR signal to decay in the transverse plane.
What can affect change image/signal intensity?
Parameters
What increases T2?
Increased tissue water and loss of cellular structure
What types of images do T1 weighted MRIs produce?
High resolution anatomical images -1 mm spatial resolution
What colour is CSF and Fat in T1 weighted MRI?
CSF appears black and fat appears white
What can T1 weighted MRIs detect?
- Can detect degenerative changes
- Developmental abnormalities
- Disease specific changes
What is unique about T1 weighted MRIs?
Cannot achieve this grey/white matter contrast in a CT image
What is the composition of grey matter?
Mostly cell bodies
Water in both the intra and extracellular compartments has relatively free motion
What is the composition of white matter?
Longer axons that connect different parts of white matter together
Myelinated
Approx. 50% of the tissue volume is accounted for by myelin structures within which T1 relaxation of 1H in lipids structures is very short
How do protons in fatty tissue in the myelin sheath affect the changes in signal intensity?
Interaction of myelin protons and water protons in axons changes signal intensity
What do degenerative changes in tissue cause?
It causes structural changes (i.e. demyelination, increased water content), also changes MRI properties so signal intensity on image changes which can be seen.
How was the early cortical folding process in preterm newborn brains mapped?
It was seen by T1W imaging throughout the cortex as it developed. The cortex became more convoluted and the myelination changes
Why are long myelinated axons important?
They are important to allow electrical signals to progress from one part of the brain to another.
What happens when there is MS?
Myelination is lost = dysfunction in parts of the brain
What is contained within the myelin sheath?
Microfilament/tubule bundles containing water which causes signals
How does the brain connectivity affect the MRI?
Measure diffusion of water in different orientations of the brain
- If same: isotropic diffusion
- If different: anisotropic so can be related to white matter pathways
What are MRA?
3D MR angiography of the brain
- Shows blood vessels
- Uses magnetic field and pulses of radiowave energy to prvide a good picture of the blood vessels
- Very short TR of about 10ms used
How is the colour contrast made in the MRA?
Inflowing blood provides high signal against a darker background tissue signal
What increases blood flow and why is this important?
Increase Glc and O2 extraction leads to increased blood flow which leads to reduced Hb and so an MRI signal increase.
Describe the flow of Oxy-Hb
It moves from arterial to venous side - the O2 is released to brain parenchyma. This leaves de-oxy Hb which is paramagnetic.
How does de-oxy blood cause a reduction in signal intensity?
When there is non-uniform magnetic field (due to de-oxy Hb)
Which side of the brain has lower signal intensity than in the artery?
Venous side of the brain
What happens when O2 and glucose is constantly removed?
More O2 and glucose is required to places where it is needed to increase blood flow and less deoxy-Hb
What is a PET scan?
Positron Emission Tomography Scan
Why are PET scans used?
- Enables imaging of particular chemicals
- Radioactive nucleus decays by releasing positron
How does a PET scan work?
- If an injected substance contains radioactive nuclei, the nuclei will spread out in the rest of the body, eventually releasing gamma rays.
- These gamma rays can be detected
- Radionuclides are incorporated into pharmaceuticals that are specific for metabolic processes or cell receptors
- The injected radiopharmaceutical generates a localised gamma ray signal relating to metabolism or cellular function.
- This shows the organs are functioning
