Global Brain Activity Flashcards
Most important electrolyte influencing the brain:
- sodium
- potassium has significant peripheral
presence hence will affect the heart
which will affect the brain - calcium, magnesium and phosphate
Sodium and the Brain:
- major osmotically active solute in
ECF - hyper>145mmol/L
- hypo<135mmol/L
Acute Hyponatremia:
- low level of sodium outside of the
cells - water will move into the cells
- cells swell leading to cerebral
oedema - decreased blood flow
- cerebral compression
to compensate:
- will shift CSF into systemic circulation
- then will push K+ out of cells to make
water follow
- release of osmolytes like
glutamine,mate, taurine
Chronic hyponatremia:
may be asymptomatic due to the adaptations
Cerebral Oedema: Symptoms:
- nausea
- vomiting
- anorexia
- headaches
- lethargy
- disorientation
- muscle cramps
Cerebral Oedema: Signs:
- seizures
- coma
- hyporeflexia
- respiratory depression
- hypothermia
What is shown below?
Areas of herniarion
Central Pontine Myelinolysis (osmotic demyelination syndrome)
- result of rapid overcorrection of low
sodium in ECF - in cases of chronic hyponatremia
(asymptomatic) (swollen cells) - slow correction needed to prevent
fluid shift damaging cells - demyelination due to death of
oligodendrocytes
shrink cells by adding sodium or restricting fluid intake
Hypernatremia:
- too much sodium in ECF
- water will move into the ECF
- cells shrink
- haemorrhage from veins and
arteries due to tearing
Compensation:
- uptake of potassium into cells
- uptake of osmolytes into cells
(glutamine,mate,taurine)
- ^^^protective against cell damage
overcorrection can cause cerebral oedema
hyponatremia
hypernatremia
insert diagram
Acid-Base Disorders:
- acidemia = <7.35
- alkalosis = >7.45
- CO2 can cross the BBB easily
- CO2 regulates cerebral blood flow
- compensatory metabolic correction
when there is a chnage in CO2
(ventilation) - hyperventilation in resp alkalosis:
less CO2 reduces cerebral blood flowlightheadedness, syncope, seizures,
hypocalcaemia - hypoventilation in resp acidosis: too
much CO2, increase cerebral blood
flow, increases pressuremorning headaches, visual
disturbances and confusion
As CO2 increases, effect on cerebral blood flow?
increases till plateau
Acid-base disorder:
other electrolyte disturbances
Which chemical regulates cerebral blood flow?
- O2
- Na+
- CO2
- K+
- H2O
CO2
Na+ will affect but will not regulate
A patient is suspected to have obesity-hypoventilation syndrome. What symptom form the history would support this diagnosis?
- pins and needles in the legs
(parasthesia) - morning headaches
- clumsiness when walking (ataxia)
- chest pain
morning headaches
Pneumocephalogram
- stopped in the 1970s
- inject air via lumbar puncture
- rotate the patient
- painful
CAT (Computerised axial tomography):
- based on x ray processed in an arc
and processed into cross-sectional
image - based on density
- low resolution but quick
- with or without contrast for
breakdown of the blood brain barrier - vascular imaging using an iodine dye
CAT Diagrams:
What is density measured in?
Hounsfield Units
density of CT scans can be altered by windowing and leveling
Pros of CT Scans:
- quick
- metal: compatible
- cheap
Cons of CT Scans:
- low resolution especially posterior fossa
- radiation
MRI:
- magnetic fields and radiofrequency
energy - high resolution
- based on intesnity
- with or without gadolinium based
contrast agents GAD
Using a dye or contrast when imaging the brain:
- BBB consists of tight junctions
- dye will remain in the vascular
system - injury to the BBB leads to leakiness
and hence dye would be visible
throughout the brain
MRI: Pros:
- detailed
- wide range of imaging possibilities
- no ionising radiation
MRI Cons:
- metal is an issue
- claustrophobia
- time consuming so prone to motion
artefact - loud
- can heat up the body
Functional MRI (fMRI):
- brain has no energy stores and
requires glucose - glucose needs to be transported to
the brain and causes arterioles to
dilate - signal characteristics of oxy and
deoxy haemoglobin indirectly
measures local neuronal activity
based on this vascular response (no
dye) - poor spatial and temporal resolution
What is the default mode network?
- activity of the brain when doing
nothing:- medial prefrontal cortex
- medial parietal cortex
- medial temporal lobes
- consolidation and info processing,
internalised thought, affected in
ADHD, schizophrenia, autism and
alzheimers
SPECT:
- single photon emission computed
tomography - used in neurology, oncology and
cardiology - 2D images from multiple angles then
reconstructed into a 3D image - uses isotopes with longer decay
times and emit a single instead of
double gamma rays - can be combined with CT
- worse spatial resolution and more
radiation than PET4
