Homeostasis

Question 1

What is the neuronal microenvironment composed of?

Answer 1

Glia, capillaries, other neurons, and extracellular space which is made up of:
extracellular matrix and brain extracellular fluid

Question 2

What happens to the BECF when neuronal activity is increased?

Answer 2

Increase in K+
Changes in Ca2+, O2, CO2, glucose concs
Neurotransmitter concs

Question 3

How would an increase in extracellular K+ impact neurons?

Answer 3

Elevate resting potential and therefore bring the cell closer to the threshold for firing action potentials
Increased neurotransmitter release which could lead to unspecific receptor activation

Question 4

How was the blood brain barrier discovered?

Answer 4

Intravenous injection of dyes

Dye pass across leaky tissues and stain them, apart from in the brain where there was no staining

Question 5

What is the blood brain barrier? What is it’s function?

Answer 5

Barrier preventing free movement of substances from plasma into the BECF
It protects neurons from fluctuating concentrations of substances in the blood

Question 6

Examples of fluctuations in the blood that the blood brain barrier protects the brain from

Answer 6

High amino acids after a meal
High K+/H+ after exercise
Circulating hormones, inflammatory mediators and toxins

Question 7

How is the blood brain barrier maintained?

Answer 7

Tight junctions between endothelial cells
Thick basement membrane
Astrocytic endfeet

Question 8

How do important molecules get past the blood brain barrier?

Answer 8

Facilitated transport
Exchangers
Co-transporters
Increased number of mitochondria for AT
Small, uncharged or lipid soluble molecules can go through more easily

Question 9

What are the leaky areas of the blood barrier? Why are they?

Answer 9

Choroid plexuses are circumventricular organs which make cerebrospinal fluid so they have to have a level of leakiness

Question 10

Why do we need leaky areas of the blood brain barrier?

Answer 10

For the secretion of cerebrospinal fluid
Hormones
Cytokines and mediators

Question 11

Describe the flow of cerebrospinal fluid. What is the function of this?

Answer 11

Secreted by the choroid plexus
Circulates around ventricles and central canal
Absorbed from subarachnoid space to venous blood via the superior sagittal sinus
Removal of waste products + maintainance of ion concs

Question 12

How is CSF secreted?

Answer 12

Ultra filtration of plasma into ECF across normal leaky capillaries
Selective absorption of substances into CSF across choroidal epithelial cells
Free movement of substances from CSF to BECF across ependymal cells

Question 13

What is the difference in composition between CSF and normal plasma?

Answer 13

Lower in potassium, amino acids and proteins

Question 14

What are the three types of meninges (outwards in order)? What are their functions?

Answer 14

Dura mater- thick inelastic membrane, split into 2 layers to form intracranial sinuses
Arachnoid mater- cells linked by tight junctions to prevent diffusion between plasma and CSF
Pia mater- covers surface of brain and blood vessels and allows diffusion between CSF and BECF

Question 15

What is the subarachnoid space?

Answer 15

Space in between the arachnoid mater and the pia mater

Question 16

What substances are moved from the BECF to the CSF?

Answer 16

Metabolic waste products

Neurotransmitters

Question 17

What substacnes are moved from the CSF to the BECF?

Answer 17

Macronutrients, micronutrients, ions

Question 18

What is hydrocephalus? What symptoms does it cause?

Answer 18

Lack of circulation of CSF leads to dilation and obstruction of ventricular system or interrupted CSF absorption
Increased intracranial pressure, loss of cells within brain and loss of brain stem reflexes

Question 19

How do increases in extracellular K+ effect astrocytes?

Answer 19

Increased glucose metabolism and increased K+ uptake

Question 20

What is the function of the astrocytic syncitium? How is it created?

Answer 20

Created by gap junctions
Allows spatial buffering and redistributes K+ to areas of decreased activity
Can transport sugars, amino acids, cAMP and Ca2+

Question 21

What role do astrocytes play in terms of neurovascular coupling?

Answer 21

Increase in neuron firing rate
increase in astrocyte Ca2+
release of vasoactive substances from astrocyte
blood vessel diameter increases

Question 22

What imaging techniques measure brain activity? How do they do this?

Answer 22

fMRI- functional magnetic resonance imaging exploits oxygen use
PET- positron emission tomography exploits glucose use

Question 23

How does fMRI work in detail?

Answer 23

MRI uses an electromagnetic wave to disrupt hydrogen atom state
Oxyhaemoglobin and deoxyhaemoglobin distort the magnetic resonance properties of hydrogen atoms differently so active areas can be identified