Global Brain Activity Flashcards
How does CSF differ from serum?
Less protein & less K
Similar Na & HCO3 & osmolality
What is homeostasis?
Maintenance of the environment to optimise conditions for the brain to work.
Which is the most important ion in terms of osmosis?
Na - H2O follows Na.
Where does K+ levels have significant influence?
In the peripheral system - important in maintaining the heart beating at the right pace.
How is acid-base balance affected by ventilation?
Hypoventilation - acidosis
Hyperventilation - alkalosis
What is the normal values of Na in the blood?
135-145
What is hyponatremia?
Low levels of Na outside the cell - means the intracellular content of Na is higher - so water floods into cells causing cerebral oedema
How does the brain try to compensate for hyponatremia?
Shifts out the CSF & pushes K+ & osmoloytes out of the cells trying to draw the water out.
How does cerebral oedema affect the blood flow to the brain?
It causes decreased blood flow.
What is the difference between acute and chronic hyponatremia?
Acute - no time to adapt - cerebral oedema & compression can occur.
Chronic - body is able to adapt if the hyponatremia is gradual.
How does carbamazepine affect Na levels?
Causes hyponatremia.
How does compression of the brainstem affect breathing regulation?
It can depress breathing
What is central pontine myelinolysis?
Hyponatremia = swollen cells - if you treat (with Na) and overcorrect - can cause shrunken cells - this damages the cytoskeleton of the cell & demyelinates neurons –> problems.
What are the symptoms of Central Pontine Myelinosis?
Quadriplegia
Emotional incontinence
Seizures
Coma
Death
Pseudobulbar Palsy
What is Central Pontine Myelinosis caused by?
Rapid overcorrection of low Na levels.
What is hypernatremia?
Lots of Na in the interstitium - water leaves cells and moves to the extracellular space = shrinkage of cells.
How can hypernatremia affect veins and arteries?
It can cause them to tear & haemorrhage
What does the brain do to try and compensate for hypernatremia?
Uptakes K+ into cells
Uptakes osmolytes into the cells
What can overcorrection of hypernatremia cause?
Cerebral oedema
What is the ideal pH range for the brain?
7.35 - 7.45
What does the Henderson Hasselbach equation demonstrate?
That there is an inverse relationship between HCO3 and CO2.
Can CO2 cross the BBB?
Yes - easily
What regulates cerebral blood flow?
CO2 levels in the brain (more CO2 - inc BF & vice versa)
How does hyperventilation affect Ca?
Causes hypocalcemia.
What are the symptoms of hyperventilation?
Lightheadedness, syncope, seizures & hypocalcaemia
What are the symptoms of hypoventilation?
Morning headaches, visual disturbances, confusion
How does hypoventilation affect the brain?
Increased CO2 = inc blood flow to the brain - causing increase pressure - - headaches, disturbances and confusion.
Apart from Na, K, HCO3 - which other ions have impacts on the brain?
Ca, Mg & P
Ca & Mg - help stabilise neuronal signalling pathways - so low levels = abnormal firing.
What is it called when the brain is affected by an external agent or condition.
Encephalopathy
Hypocalcaemia is associated with low/high levels of which ions?
Low K & Mg
High P
What does a CT scan with contrast show?
If there is breakdown of the BBB
What are CT scans based on?
Density of different materials
What does windowing and levelling do?
Allows you get change the pictures you get - and therefore see different materials with different densities - e.g. brain window, bone window, blood window.
What are the pros of CT?
Quick
Metal compatible
Cheap
What are the disadvantages of CT?
Low resolution - esp brainstem / cerebellum
Radiation dose
What does CT use to image?
Lots of X-rays
What does MRI use to image?
The magnetism of proton molecules
Why is MRI preferable over CT?
You get more detailed pictures with MRI than CT
How can dye show if the BBB is leaky?
Dye should remain in the arterial / vascular systems - if there is an injury to the BBB you will get leakiness of the dye into other areas.
What are the pros of MRI?
Detailed
Wide range of imagining possibilities
No ionising radiation
What are the cons of MRI?
Metal = issue
Claustrophobia
Time consuming
Loud
Can heat up the body
What is an fMRI?
Uses characteristics of oxy & deoxy - measures local neuronal activity based on vascular response to glucose - shows which areas of the brain are metabolising glucose.
How does transport of glucose affect vessels?
Causes the BVs to dilate
What are default areas on an fMRI?
Areas where the brain is always metabolising - is the background system running when no specific task is assigned.
How does PET-CT work?
Injection with radioactive substance - uses CT to outline where in the body this is.
What are the cons of PET-CT?
Radioactive isotopes
Very expensive - used sparingly
What is used to determine whether a tremor is Parkinsons?
SPECT (single photon emission computed tomography)
