11/ homeostasis in the nervous tissue

Question 1

what is the neural microenvironment composed of

Answer 1

glia, capillaries, other neurons, extracellular space (extracellular matrix, brain extracellular fluid BECF)

Question 2

relationship between influences of BECF and neurons on each other

Answer 2

• BECF can both influence and be influenced by neurons
• becf composition must be tightly regulated - if not neuronal disfunction and death

Question 3

how could neuronal activity change the composition of the becf

Answer 3

• most important increased K conc - usually v low (not big Na change since there’s loads already)
• increased H ions - increased acidification
• changes in neurotransmitter conc

Question 4

how could change in becf composition change neuronal activity

Answer 4

• increased K conc in becf could elevate resting potential, closer to ap threshold - cells more excitable
• increase in nt release - lead to unspecific receptor activation and unspecific neuronal activity

Question 5

4 ways we regulate becf

Answer 5

blood brain barrier
CSF in ventricular system
neurons
glial cells (astrocytes)

Question 6

what experiment showed bbb

Answer 6

• intravenous injection of dyes
• dyes pass across leaky capillaries and stain soft tissue
• no staining in the brain - must have tighter junctions

Question 7

function of bbb, examples

Answer 7

• protect neurons from fluctuations in conc of substances in blood
• eg increased aa after a meal (can act as nt)
• increased K and H ions after exercise
• hormones
• inflammatory mediators
• toxins

Question 8

how is bbb maintained

Answer 8

• tight junctions between endothelial cells prevent paracellular route
• thick bm
• astrocytic endfeet - surround capillaries, make a thicker barrier around the capillary

Question 9

what types and examples of molecules can pass into bbb more easily

Answer 9

• small, uncharged, lipid soluble
• co2, o2, nicotine, caffeine, heroin

Question 9

how do important molecules cross bbb

Answer 9

• transcellular route
• facilitated transport - exchangers, co-transporters, active transport (increased mitochondria)

Question 10

what are the leaky regions of the bbb

Answer 10

• choroid plexuses - ventricular system
• circumventricular organs - around circumference of ventricles

Question 11

why are there leaky areas of bbb

Answer 11

• hormone release from hypothalamus and pituitary gland
• to detect things that allow our brain to respond through homeostasis
• osmoreceptors - OVLT, SFO - hypothalamus
• temp control centres - cytokines eg OVLT