Global Brain Activity

Question 1

Although CSF is similar to plasma, there are 2 key differences, where the concentrations are lower in CSF than in plasma. What are these 2 differences?

1. CSF has higher K+ and amino acid concentration than plasma
2. CSF has lower K+ and a higher amino acid concentration than plasma
3. CSF has higher K+ and a lower amino acid concentration than plasma
4. CSF has lower K+ and amino acid concentration than plasma

Answer 1

4. CSF has lower K+ and amino acid concentration than plasma

• K+ (plasma = 4.7 and CSF = 2.9mEq)
• amino acids (plasma = 2.6 and CSF = 0.03mEq)

Question 2

What is the glymphatic system?

Answer 2

• a waste clearance in the CNS, essentially a lymphatics system of the brain
• CSF flows into the paravascular space around cerebral arteries, combining with interstitial fluid and parenchymal solutes, and exiting down venous paravascular spaces

Question 3

What are the 2 methods by which CSF is able to leave the brain?

1. diffuse into veins and ventricles
2. arachnoid granulation and diffusion into veins
3. arachnoid granulation and glymphatic system
4. glymphatic system and ventricles

Answer 3

3. arachnoid granulation and glymphatic system

1 - arachnoid granulation (into venous sinus and out through internal carotid artery), likely superior sagittal sinus

2 - through glymphatic system (brains lymphatic system)

Question 4

What does hypertonic (relative to extracellular fluid) mean?

Answer 4

• fluid outside of the cell has a high osmolarity
• solute concentration in the cell is lower than fluid surrounding it
• cations/anions leave the cell to dilute and water follows
• cell shrinks

Question 5

What does hypotonic (relative to extracellular) mean?

Answer 5

• fluid outside of the cell has a low osmolarity
• solute concentration in the cell is higher than fluid surrounding it
• cations/anions enter the cell to dilute and water follows
• cell expands and can rupture

Question 6

What does isotonic mean?

Answer 6

• solute concentration in the cell is equal to outside the cell
• cations/anions do not move
• cell remains stable

Question 7

What is hypernatremia and hyponatremia?

Answer 7

• hypernatremia = high levels of Na⁺
• hyponatremia = low levels of Na⁺

Question 8

Cells of the brain tend to operate at isotonic states. What will happen if there is a sudden decrease in Na+ concentration in the extracellular fluid in the brain?

Answer 8

• fluid will flow into the intracellular compartments of the brain to dilute Na+ concentration inside the cell
• cells in the brain will swell as water follows Na+
• causes cerebral oedema

Question 9

Cells of the brain tend to operate at isotonic states. If there is a sudden decrease in Na+ concentration in the extracellular fluid the fluid will flow into the intracellular compartments of the brain and the cells in the brain will swell, which will causes cerebral oedema. If the brain swells what can happen to the blood vessels of the brain?

Answer 9

• they become compressed
• blood flow will be decreased
• causes cerebral compression

Question 10

Cells of the brain tend to operate at isotonic states. If there is a sudden decrease in Na+ concentration in the extracellular fluid the fluid will flow into the intracellular compartments of the brain and the cells in the brain will swell, which will causes cerebral oedema. If the brain swells the can compress blood vessels in the brain, blood flow will be decreased and this will cause cerebral compression. There is a safety system in place in the brain that can help to remove excessive CSF if there is too much fluid in the brain, what is this safety system?

1. plug release
2. pressure stop valve
3. pressure compressor

Answer 10

2. pressure stop valve

• CSF is removed through arachnoid granulations
• CSF then enters the venous system and out through internal jugular vein

Question 11

If there is too much fluid in the brain, the pressure stop valve is able to remove CSF through arachnoid granulation, into the venous sinus and then out of the brain via the internal jugular vein. In addition to this what 2 other charged molecules can cells secrete in an attempt to increase the hypo-osmotic concentrations in the extracellular fluid?

1. Na+ and K+
2. K+ and amino acids
3. Ca2+ and amino acids
4. K+ and Cl-

Answer 11

2. K+ and amino acids

• amino acids (AA) (glutamine, glutamate, taurine)
• pumping out K+ and AA reduces osmolality inside the cell
• reduces the risk of fluid flowing into the cells causing cerebral oedema
• THIS is a slow process by the body to maintain homeostasis

Question 12

Cerebral oedema is when there is too much fluid in the brain, and is generally due to hyponatraemia (low Na+) in the extracellular space. This can cause cause fluid to flow into cells, which is dangerous in the brain as the brain can swell causing nerve death. What are a few of the most common symptoms patients may present with if they are hyponatraemic?

Answer 12

• • nausea
• • vomiting
• • anorexia
• • headaches
• • lethargy
• • disorientation
• • muscle cramps

Question 13

Cerebral oedema is when there is too much fluid in the brain. What are the most common signs that clinicians can see in patients?

Answer 13

• • seizures
• • coma
• • hyporeflexia
• • Cheyne-Stokes respiration (gradual increase, decrease, apnea then stop)
• • respiratory depression
• • hypothermia

Question 14

What does central pontine myelinolysis, also referred to as osmotic demyelineation syndrome) mean if we break down the name?

Answer 14

• pontine = refers to pons of the brain stem
• myelin = refers to myelin that covers axons
• sis = indicates destruction
• so destruction of myelineated axons in the pons due to osmotic changes

Question 15

The following can occur in patients who are hyponatremic (low Na+):

• low extracellular Na+ = fluid flows into the cells to maintain osmosis (dilute intracellular concentration), causing oedema.
• cells of the brain try to mediate this by secreting K+ and other osmolites (amino acids and glucose) to lower intracellular concentrations. This will stop water entering cells and maintain osmosis, but can take up to 48 hours.
• clinician may attempt to correct the Na+ imbalance too quickly and give the patient high Na+ fluids. The cells do not have sufficient time to correct the osmotic balance as Na+ cannot easily enter the cell and it takes time for K+ and osmolites to re-enter the cell.
• patient becomes hypertonic = high Na+ extracellularly, meaning water leaves the cell to dilute extracellular Na+ and maintain osmosis and the cells shrink

This can damage the cells and even cause cell death. What is this called if this occurs in the pons of the brain?

1. Central Pontine Myelinolysis
2. myasthenia gravis
3. multiple sclerosis
4. neural infarct

Answer 15

1. Central Pontine Myelinolysis, also called osmotic demyelination syndrome

Question 16

Central Pontine Myelinolysis, also called osmotic demyelination syndrome is damage to the myelineated axons located centrally in the pons. This can be very serious, given how important the pons are in communication between the spinal cord and the cerebral cortex. What can this lead to for the patient?

Answer 16

• • quadriplegia (paralysis from the neck down)
• • pseudobulbar palsy (inability to control muscles)
• • seizures
• • coma
• • death

Question 17

Cells of the brain tend to operate at isotonic states. What will happen if there is a sudden increase in Na+ concentration in the extracellular fluid in the brain?

Answer 17

• • fluid will flow out of the extracellular compartments of the brain to equalise Na+ concentrations
• • fluid will leave cells to reduce hypertonic Na+ extracellularly
• • cells in the brain will shrink
• • causes haemorrhage from veins and arteries and reduced cerebral blood flow

Question 18

Cells of the brain tend to operate at isotonic states. If there is a sudden increase in Na+ concentration in the extracellular fluid in the brain, water will flow out of the cell to maintain osmosis. Thus can cause the cells to shrink causing haemorrhage in veins and arteries. What do the cells of the brain try to do in an attempt to compensate for this?

Answer 18

• cell increase K+ and amino acid uptake to achieve equilibrium with outside of the cell, so water will not leave the cell, causing the cells to shrink
• aim is to maintain osmosis with outside of the cell

Question 19

Cells of the brain tend to operate at isotonic states. If there is a sudden increase in Na+ concentration in the extracellular fluid in the brain water will flow out of the cell to maintain osmosis. Thus can cause the cells to shrink causing haemorrhage in veins and arteries. The cells of the brain try compensate for this by increasing K+ and amino acid uptake with the aim of maintaining osmosis with outside of the cell. However, if we overcorrect this with treatment what can happen?

Answer 19

• outside of the cell becomes hypotonic
• fluid rushes into cells to maintain equilibrium with outside of the cell causing cerebral oedema

Question 20

What is the Henderson Hasselbach equation?

Answer 20

• pH is a relationship between an acid and a base ratio
• low pH = acidemia
• high pH = alkalosis

Question 21

What gas is the main contributor to have cerebral blood flow is regulated?

1. CO2
2. O2
3. H2

Answer 21

1. CO₂
   - because it is able to cross the blood brain barrier

Question 22

What is the relationship between arterial PCO2 and cerebral blood flow, keeping in mind that CO2 in the body is a powerful vasodilator.

Answer 22

• increase in arterial PCO2 = increase in cerebral blood flow
• decrease in arterial PCO2 = decrease in cerebral blood flow

Question 23

The relationship between arterial PCO2 and cerebral blood flow is as follows:

• increase in arterial PCO2 = increase in cerebral blood flow
• decrease in arterial PCO2 = decrease in cerebral blood flow

Therefore if we hyperventilate, which is an increase in breathing rate and/or volume we will expel more CO2, causing a reduction PCO2. This in turn will cause vasoconstriction in cerebral blood flow. What can this cause in patients?

Answer 23

• • lightheadedness
• • syncope (fainting)
• • seizures
• • cramps
• • parasthesias (burning or prickling sensation, generally in hands)
• • chvosteks sign (low Ca2+ causes muscle twitches in face upon tapping)

Question 24

The relationship between arterial PCO2 and cerebral blood flow is as follows:

• increase in arterial PCO2 = increase in cerebral blood flow
• decrease in arterial PCO2 = decrease in cerebral blood flow

Therefore if we hyperventilate, increase in breathing rate and/or volume we will expel more CO2, causing a reduction in cerebral blood flow. This cause lightheadedness, syncope (fainting), seizures, cramps, parasthesias (burning or prickling sensation) and/or chvosteks sign (low Ca2+ that causes muscle twitch in the face with touched). What is a simple way to treat this?

Answer 24

• • breathe into a paper bag
• • CO2 is trapped and you will re-breathe in more CO2
• • PCO2 levels increase and thus increase cerebral blood flow

Question 25

The relationship between arterial PCO2 and cerebral blood flow is as follows: - increase in arterial PCO2 = increase in cerebral blood flow - decrease in arterial PCO2 = decrease in cerebral blood flow Therefore if we hypo-ventilate, shallow and/or slow breathing we will not expel enough CO2, causing an increase in cerebral blood flow and an increase in the pressure on the brain. What can this cause in patients?

Answer 25

* - reduced pH and acidosis * - morning headaches * - visual disturbances * - confusion

Question 26

What is encephalopathy, which is greek for suffering brain?

Answer 26

- damage to the brain - brain function is impaired

Question 27

What is Encephalitis, where enkephalos is greek for brain and itis is inflammation. What does this mean?

Answer 27

- inflammation of the brain

Question 28

Amyloid precursor protein (APP) is a transmembrane protein (half in and outside the cell) that is involved in neuronal cell growth and repair. Once its function is completed it is soluble and removed after it is broken down by alpha and gamma secretase. However, if gamma and beta secratase break down the APP, what can this lead to?

Answer 28

* part of the APP remains and is not soluble * creates monomer beta-amyloid that then clump and stick together

Question 29

What is amyloid?

Answer 29

- a proteins that take on an abnormal shape due to impaired folding - makes them group together and stick in organs and tissue - hypothesised to be extracellular cause of Alzheimer’s

Question 30

Amyloids are proteins that have folded incorrectly. They can then coagulate, sticking to tissues and organs and impairing their function. What can happen in the brain?

Answer 30

- cerebral amyloid angiopathy (disease of blood vessels) (CAA) - amyloid build up on the walls of the arteries in the brain leading to increased risk of haemorrhage causing stroke and dementia - in Alzheimer's amyloids block neurons and they cannot function

Question 31

Whenever we look at pictures from imaging technologies, how do we tend to look at the image?

Answer 31

- from the feet up to the head - left = right - right = left

Question 32

What is a computerised tomography (CT), also referred to as a CAT scan?

Answer 32

- multiple X-rays applied using an arch like machine - provides a cross sectional image of the patient - based on density, more density = whiter

Question 33

In a computerised tomography (CT) scan, why can it be useful to use a contrast dye specific for the brain?

Answer 33

- look at brain perfusion - estimates blood flow in brain - important in strokes

Question 34

What plane is the section cut and what type of imaging has been used in the image below?

Answer 34

- axial/transverse slices - CT because the skull is super bright (remember X-rays)

Question 35

What is the benefit of having a CT scan on a computer when compared to an X-ray?

Answer 35

- X-ray has 5 basic densities (bone, metal, fat, air, fluid) - CT can be changed on a scale making it easier to distinguish between tissues of similiar densities - changing of the scale through windowing and levelling

Question 36

What are the benefits and negatives of CT scans?

Answer 36

- pros = quick, metal compatible, cheap - cons = low resolution and radiation is used

Question 37

What are the pros and cons of MRI imaging?

Answer 37

- pros = detailed, wide imaging possibilities, no ionising radiation - cons = metal is a problem due to magnet (pacemaker), claustrophobia, time consuming, loud and can heat tissues

Question 38

How does a functional MRI (fMRI) differ from a standard MRI?

Answer 38

- fMRI = images based on metabolism and blood flow - MRI = images based on anatomical structure

Question 39

Functional MRI measures blood flow and metabolism. How does it do this?

Answer 39

- brain has no energy store and needs constant glucose in blood - glucose dilates arterioles in the brain to get glucose - fMRI measures difference between oxy and deoxy haemoglobin

Question 40

What is an issue of functional MRI imaging?

Answer 40

- poor spatial and temporal resolution

Question 41

What is default mode network which is measured through functional MRI?

Answer 41

- the brain when it is said to be at rest or not doing anything - despite no instructions patterns in blood flow are common

Question 42

The default mode network which is measured through functional MRI is the brain when it is said to be at rest or not doing anything. Despite no instructions patterns in blood flow are common. What are the 3 places it is common numbered 1-3 in the image?

Answer 42

1 - medial temporal cortex 2 - medial prefronal cortex 3 - medial parietal cortex

Question 43

What does the posterior cortical hot zone, or just hot zone refer to in the brain?

Answer 43

* no instructions are given to patients when imaging the brain * patterns in blood flow can be seen * common posteriorly, medial temporal cortex, medial pre-fronal cortex and medial parietal cortex

Question 44

What is nuclear medicine?

Answer 44

- an isotope specific to a tissue is injected - this isotope emits radioactivity that can be detected on gamme imaging - PET

Question 45

What can a DaTscan, that uses a dopamine transporter to ioflupane 123 be useful for?

Answer 45

- distinguish between parkinsons disease and essential tremour - in parkinsons disease the dopamine transpoort system is affected, therefore we can see this in imaging