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Neuroscience > CNS homeostasis > Flashcards

CNS homeostasis Flashcards

1
Q

What is in the extracellular space of the brain? (2)

A
  • Extracellular matrix

- Brain extracellular fluid (BECF)

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2
Q

How could BECF composition be affected by increased neuronal activity?

A
  • Increased K+ concentration
  • Changes in Ca2+
  • Changes in glucose, CO2, O2 conc.
  • Increased neurotransmitter concentrations
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3
Q

How could a change in BECF composition change neuronal activity?

A
  • Increased K+ concentration in BECF could bring the resting potential closer to the threshold for action potential
  • Increased neurotransmitter conc. could caused unspecific receptor activation and unspecific neuronal activity
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4
Q

How is the neuronal microenvironment regulated? (4)

A
  • Blood brain barrier
  • Cerebrospinal fluid (CSF) in the ventricular system
  • Neurons
  • Glial cells
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5
Q

How was the blood brain barrier discovered?

A
  • Intravenous dyes injected into mice
  • Soft tissues were stained
  • No staining in the brain
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6
Q

What is the function of the blood brain barrier?

A
  • To protect neurons from fluctuations in concentrations in substances in the blood
  • E.g. increased amino acids in the blood after a meal could stimulate neurons in the brain without regulation, ions after exercise, hormones, toxins etc.
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7
Q

How is the blood brain barrier maintained? (3)

A
  • Tight junctions between endothelial cells eliminate the paracellular route
  • Thick basement membrane
  • Astrocytic endfeet (from glial cells - astrocytes)
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8
Q

How do necessary molecules get through the blood brain barrier?

A
  • Facilitated transport
  • Exchangers
  • Co-transporters
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9
Q

Which organelle is needed in increased numbers in the blood brain barrier?

A

Mitochondria for active transport

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10
Q

Which molecules can pass easily through the blood brain barrier?

A
  • Small, uncharged, lipid soluble

- E.g. O2, CO2, nicotine, heroin, caffeine

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11
Q

Which drugs can easily pass through the blood brain barrier? (3)

A
  • Nicotine
  • Heroin
  • Caffeine
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12
Q

What are the 2 main leaky regions of the blood brain barrier?

A
  • Choroid plexuses (ventricular system)

- Circumventricular organs

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13
Q

What are ependymal cells?

A

Ciliated-epithelial glial cells

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14
Q

Why do we have leaky areas of the blood brain barrier? (3)

A
  • Hormone release from the hypothalamus and pituitary gland
  • Osmoreceptors
  • Temperature control centres
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15
Q

What is the ventricular system?

A

A set of 4 connected cavities in the brain filled with cerebrospinal fluid

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16
Q

What is the purpose of cerebrospinal fluid?

A
  • Provides physical protection to the brain against the skull, makes it effectively “lighter”
  • Maintains appropriate levels of ions in then brain by adding/removing waste products
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17
Q

What is the central canal?

A

Thin tube which is continuous with the fourth ventricle and goes down the spinal chord

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18
Q

What are foramens?

A

Gaps which allow the cerebrospinal fluid out of the central ventricles and around the outside of the brain

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19
Q

What is the superior sagittal sinus?

A

Point where cerebrospinal fluid enters the venous system

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20
Q

Where is cerebrospinal fluid made?

A

From the choroid plexuses

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21
Q

What is the choroid plexus?

A

Secretory tissue which makes cerebrospinal fluid

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22
Q

How much cerebrospinal fluid is secreted each day?

A

500 ml per day

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23
Q

Are ependymal cells leaky or do they have tight junctions?

A

Leaky

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24
Q

What separates the CSF in the ventricles from the brain tissue?

A

Epithelium of ependymal cells

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25
Q

Is the choroidal epithelium leaky or does it have tight junctions?

A

Tight junctions

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26
Q

How is cerebrospinal fluid secreted from the choroid plexuses?

A
  • Plasma from (normal leaky) capillaries inside the choroid plexus is filtered
  • Substances are selectively absorbed into the CSF in the ventricles across the choroidal epithelium (tight junctions)
  • Substances can then move freely between the CSF and the brain tissue across leaky ependymal cells
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27
Q

What are the 2 main differences between the composition of the CSF and plasma?

A
  • CSF has lower K+ than plasma

- CSF has lower amino acid/protein concentrations than plasma

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28
Q

What are the meninges?

A

3 membranes surrounding the brain and spinal chord

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29
Q

What are the 3 types of meninges?

A
  • Pia mater
  • Arachnoid mater
  • Dura mater
30
Q

What are the leptomeninges?

A
  • Pia mater

- Arachnoid mater

31
Q

What is the pia mater? (2)

A
  • The innermost layer of the meninges which adheres to the surface of the brain and spinal chord
  • Very permeable so allows movement between the surrounding CSF and the brain extracellular fluid
32
Q

What is the arachnoid mater? (2)

A
  • Second layer of the meninges, separated from the pia mater by the CSF
  • Has tight junctions so less permeable than the pia mater
33
Q

What is the subarachnoid space?

A

Space in between the pia mater and the arachnoid mater filled with cerebrospinal fluid

34
Q

What are arachnoid granulations?

A

Protrusions of the arachnoid mater through the dura mater into the superior sagittal sinus through which CSF can enter the venous circulation

35
Q

What is the dura mater? (2)

A
  • Toughest of the meninges

- Splits into 2 layers: one follows the gyri and sulci of the brain, other layer is an outer layer

36
Q

What is a gyrus?

A

Outward bump of the cerebral cortex

37
Q

What is a sulcus?

A

Inward bump of the cerebral cortex

38
Q

What are the 2 types of evaginations of the arachnoid membrane?

A
  • Arachnoid granulations

- Arachnoid villi

39
Q

What are the 2 types of evaginations of the arachnoid membrane?

A
  • Arachnoid granulations

- Arachnoid villi

40
Q

How big are arachnoid granulations?

A

Up to 1cm

41
Q

What is the function of arachnoid evaginations?

A

Project through the dura mater into the sinus space to allow CSF to re-enter venous circulation

42
Q

How does CSF enter venous circulation?

A
  • Rise in pressure of the CSF due to constant production from choroid plexuses causes absorption of CSF into arachnoid projection cells
  • CSF taken up in membrane vesicles, fuses with basolateral side of the cell and CSF enters the sagittal superior sinus
43
Q

Where in the brain does exchange occur between the CSF and BECF? (2)

A
  • From ventricles across ependymal cells

- From subarachnoid space across the Pia mater

44
Q

Why can substances move across the Pia mater?

A

Doesn’t have tight junctions

45
Q

Which substances are transported from the CSF to the BECF? (3)

A
  • Macronutrients e.g. glucose
  • Micronutrients e.g. vitamins
  • Ions e.g. HCO3-
46
Q

Why is HCO3- needed in the BECF?

A

To prevent acidification of the brain

47
Q

Which substances are transported from the BECF to the CSF? (2)

A
  • Metabolic waste e.g. CO2

- Neurotransmitters and their breakdown products

48
Q

What is hydrocephalus?

A

A blockage in the ventricular system which means the CSF can’t drain so leads to a build-up of fluid

49
Q

What condition arises when the CSF can’t drain properly?

A

Hydrocephalus

50
Q

What does hydrocephalus cause?

A
  • Increased cranial pressure
  • Cell death in the brain
  • Loss of brainstem reflexes (regulation of heart rate etc. in the brain stem)
51
Q

What are astrocytes?

A

Specialised glial cells

52
Q

Which transporter takes glutamate back up into the presynaptic terminal?

A

EAAT3

53
Q

What is the function of EAAT3?

A

Transporter which takes glutamate back up into the presynaptic terminal

54
Q

Which transporters take up glutamate into astrocytes? (2)

A

EAAT1 and EAAT2

55
Q

What is the function of EAAT1 and EAAT2?

A

Transporters which take glutamate up into astrocytes

56
Q

What do astrocytes do with glutamate they have taken up?

A
  • Break it into glutamine

- Recycle it into the presynaptic terminal

57
Q

How can neurons and astrocytes regulate levels of neurotransmitter in the BECF?

A

Take up neurotransmitter into presynaptic terminal/astrocyte and recycle it to stop neurotransmission

58
Q

How can neurons and astrocytes regulate levels of K+ in the BECF?

A

Na+/K+ ATPases transport K+ into cells and Na+ out of cells which decreases extracellular K+

59
Q

How do increases in extracellular K+ affect astrocytes?

A
  • Increased intracellular K+ due to more uptake
  • Causes increased glucose metabolism
  • Causes increased activity of Na+/K+ ATPase to take up more K+
60
Q

Why do neurons have a resting membrane potential of -65mV but glia have a resting membrane potential of -85mV?

A
  • Neuronal membranes are more permeable to Na+ than astrocytic membranes therefore more positive resting potential
  • Astrocytic membrane have a higher K+ selectivity (more K+ than Na+)
61
Q

Why are astrocytes more sensitive to changes in extracellular K+ than neurons?

A

Astrocytes have higher K+ selectivity than neurons

62
Q

What is an astrocytic syncytium?

A

Where adjacent astrocytes are joined via gap junctions

63
Q

What do astrocytes do when they have increased intracellular K+?

A

K+ is distributed through the astrocytic syncytium via gap junctions to areas with lower activity/lower K+ concentration

64
Q

What are gap junctions made of?

A

Individual connexins join to make a connexon which forms a pore

65
Q

What is neurovascular coupling?

A

Coupling of astrocytes to the vascular system

66
Q

What does increased neuron firing rate cause in astrocytes?

A

Increased intracellular Ca2+ in astrocytes

67
Q

How is neurovascular coupling beneficial to neurons?

A
  • Increased neuronal firing rate causes increased intracellular calcium in astrocytes
  • Leads to the release of vasoactive substances from the astrocyte
  • Can cause blood vessel dilation which increases blood supply to that area
68
Q

What do MRIs show?

A

3D structural images of the brain (not activity)

69
Q

How can brain activity be detected?

A
  • Changes in blood flow to different areas of the brain

- Active neurons need more glucose and oxygen

70
Q

What are the 2 techniques used to image brain activity by detecting changes in blood flow?

A
  • Positron emission tomography (PET)

- Functional magnetic resonance imaging (fMRI)

71
Q

How does positron emission topography (PET) work?

A

Exploits glucose use in the brain

72
Q

How does functional magnetic resonance imaging (fMRI) work?

A

Exploits oxygen use

Neuroscience (18 decks)

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