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MABS Neuroscience > The Neuronal Microenvironment > Flashcards

The Neuronal Microenvironment Flashcards

1
Q

what is the brain extracellular fluid?

A

neuronal microenvironment that includes the extracellular fluid (ECF), capillaries, glial cells, and adjacent neurons

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2
Q

T/F, the concentration of solutes in the brain ECF fluctuate with neural activity? Can changes in the BECF influence nerve cell behavior?

A

T; T

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3
Q

how does the blood brain barrier protect the BECF?

A

form fluctuations in blood composition

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4
Q

what influences the BECF composition?

A

the cerebrospinal fluid

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5
Q

what conditions the BECF?

A

the surrounding glial cells

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6
Q

what is the CSF?

A

a colorless, watery liquid which fills the ventricles of the brain and forms a thin layer around the outside of the brain and spinal cord in the subarachnoid space

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7
Q

what secretes the CSF?

A

choroid plexus

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8
Q

T/F, the composition of the CSF is not highly regulated?

A

F, it is highly regulated

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9
Q

what are the ventricles of the brain?

A

four small compartments each containing a choroid plexus filled with CSF

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10
Q

which of the ventricles of the brain are the largest and what do they communicate with? and through what?

A

The two lateral ventricles are the largest and each communicate with the third ventricle via the two interventricular foramina of Monro

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11
Q

how does the third ventricle communicate with the fourth ventricle?

A

The third ventricle communicates with the fourth ventricle by the cerebral aqueduct of Sylvius

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12
Q

what is the fourth ventricle continuous with?

A

the central canal of the spinal cord

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13
Q

which ventricle does the CSF escape?

A

the fourth ventricle and it flows into the subarachnoid space via three foramina:

Two laterally placed foramina of Luschka
Midline opening in the roof of the fourth ventricle, foramen of Magendie

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14
Q

the brain and spinal cord are covered by these three membranes?

A

dura mater, arachnoid mater, pia mater

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15
Q

the innermost meninges?

A

pia mater

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16
Q

the middle meninges?

A

arachnoid mater

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17
Q

the outermost meninges?

A

dura mater

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18
Q

what is the space between the arachnoid mater and pia mater called? what is this space filled with?

A

subarachnoid space

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19
Q

what is the thin layer of connective tissue?

A

pia mater

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20
Q

what is unique about the pia mater?

A

very closely applied to the surface of the brain and covers blood vessels

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21
Q

what is the innermost layer underneath the pia mater? what is this combined structure called?

A

glia limitans which adjoins the pia from the brain side and is separated from the pia by a basement membrane, the Pia adheres associated glia limitans very tightly; pial-glial membrane

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22
Q

how are the cells of the arachnoid membrane linked?

A

by tight junctions

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23
Q

what does the arachnoid membrane do?

A

isolates the CSF in the subarachnoid space from blood in the overlying vessels of the dura mater

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24
Q

what is the dura mater?

A

a thick, inelastic membrane that forms an outer protective envelope around the brain

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25
Q

how many layers does the dura mater have?

A

two layers that split to form the intracranial venous sinuses

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26
Q

since we know that the dura mater has two layers, what is formed as a result of this?

A

the intracranial venous sinuses

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27
Q

most of the CSF is produced by?

A

the choroid plexuses located in the ventricles

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28
Q

what produces most of the CSF? where is this structure located?

A

choroid plexus and capillaries form a small amount of CSF; ventricles

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29
Q

how much CSF is produced per day?

A

500 ml/day but CSF volume of 150 ml is replaced three times a day

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30
Q

how does CSF get pushed out into circulation?

A

CSF percolates throughout the subarachnoid space, then absorbed into venous blood from the superior sagittal sinus

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31
Q

how is CSF absorbed?

A

the sites of absorption are specialized evaginations of the arachnoid membrane into the venous sinus “arachnoid granulations/villi”, these are one way valves

32
Q

what types of cells line the ventricles?

A

ependymal cells which line the walls of ventricles and form gap junctions between themselves

33
Q

what is normal pressure hydrocephalus?

A

Spinal tap reveals normal pressure readings, but MRI of the head will show enlargement of all four ventricles due to infection or inflammation of the meninges damages the arachnoid villi and causes impaired CSF absorption

34
Q

what are the S/S of someone with normal pressure hydrocephalus?

A

Patients typically have progressive dementia, urinary incontinence, and gait disturbance; within 12 months the head is large due to fluid buildup, however, after 12 months, you see an in increase intracranial pressure and quality of life is diminished, the brain herniates through the foramen of magnum; treated with shunts

35
Q

how can normal pressure hydrocephalus?

A

CSF shunt to venous blood or to the peritoneal cavity helps reducing CSF pressure

36
Q

how is CSF secreted?

A

Choroid epithelial cells are bound to one another by tight junctions, which makes the epithelium an effective barrier to free diffusion

Ion concentration of CSF is rigidly maintained

Micronutrients are selectively transported

37
Q

how is CSF formed?

A

Ultrafiltration of plasma across the capillary wall into the ECF (underneath the basolateral membrane of the choroid epithelium)

Choroid epithelium cells secrete fluid into the ventricle

*CSF production occurs with a net transfer of NaCl which drives water isosmotically

38
Q

what is cerebral edema? how can it be treated?

A

net accumulation of water within the brain, treated with mannitol, large sugar molecule, that once filtered in the kidneys it stays on the urine side and retain water and pull water from the system to help reduce brain swelling

39
Q

what does not constitute as cerebral edema?

A

Cell swelling in the absence of net water accumulation in the brain

40
Q

what do we mean when cerebral edema is generalized?

A

it can be tolerated until intracerebral pressure exceeds arterial blood pressure; Sensors in the medulla detect the increased intracerebral pressure and can partially compensate by increasing arterial pressure

41
Q

what serves as monitors for the blood in the brain?

A

pineal gland, subfornical organ, and Organum vasculosum of lamina terminalis (OVLT), posterior pituitary (releases ADH-monitors osmolality), median eminence (communicates the hypothalamus to the pituitary gland) and area postrema (monitors for toxins); these organs are also called circumventricular organs or leaky regions

42
Q

what is the function of neurons within the circumventricular organs?

A

since they are directly exposed to blood solutes and macromolecules this is the part of the neuroendocrine control system for maintaining osmolality, appropriate hormone levels etc.

43
Q

what are the three major types of glial cells in the CNS? which one is most useful?

A

astrocytes, oligodendrocytes, and microglial cells; the astrocytes

44
Q

how plentiful are the glial cells?

A

10-fold more numerous than neurons, and they can proliferate throughout life

45
Q

how are astrocytes produced?

A

angiogenesis, where cells move out and then astrocytes provide scaffold for neurons to migrate and mature

46
Q

what are the functions of the astrocytes?

A

they modify and control the immediate environment of neurons

47
Q

what are the two types of astrocytes?

A

fibrous astrocytes and protoplasmic astrocytes

48
Q

describe the fibrous astrocytes?

A

long, thin and well defined processes

49
Q

describe the protoplasmic astrocytes?

A

shorter, frilly processes

50
Q

what are the microglial cells?

A

macrophages for the brain tissue, maintained at a resting state, once activated, they swell up and absorb foreign material to be removed

51
Q

what the oligodendrocytes?

A

these make up the myelin sheath for the CNS

52
Q

*what is the glial fibrillar acidic protein?

A

a protein that comprises the cytoskeleton of the astrocytes

53
Q

what is the protein that comprises the cytoskeleton of the astrocytes? can these be found on the neural cells?

A

glial fibrillar acidic protein; no because neurons are not glial cells

54
Q

what is another name for Muller Cells?

A

retinal astrocytes

55
Q

where are the Bergmann glial cells located?

A

the cerebellum

56
Q

what is the function of astrocytes?

A

contain all the glycogen present in the brain and enzymes needed for metabolizing glycogen

57
Q

how are the brains glucose needs met?

A

supplied by the blood

58
Q

how does the astrocyte function to serve the brain when their is an absence of glucose from the blood?

A

astrocytic glycogen could sustain the brain for about 5 minutes, at which brain starts dying after

59
Q

how do astrocytes serve as buffers for the neuron?

A

Astrocytes break glycogen down to glucose and even further to lactate, which is aerobically metabolized by nearby neurons

60
Q

T/F, GFAP cannot be found in the neuron?

A

True

61
Q

what is another function of the astrocytes?

review this, very confusing

A

regulate the potassium concentration in the outer layers of the neuron

neuronal activity modulates the concentration of potassium and so the astrocytes monitor potassium levels.

The accumulation of extracellular K+ that is secondary to neural activity serve as a signal to glial cells which is proportional to the extent of the activity and so they take in the potassium and it passes through gap junctions of the astrocytes to maintain ion concentration around neurons to maintain functionality, same function of Muller Cells except these operate in the retina

62
Q

what is the third function of astrocytes?

A

they can synthesize at least 20 neuroactive compounds including glutamate and GABA

63
Q

where is the glutamate precursor glutamine manufactured?

A

only in astrocytes, by astrocyte-specific enzyme glutamine synthetase

64
Q

what is glutamine released by?

A

astrocytes to the BECF to be taken up by neurons

65
Q

amino acid is important for GABA synthesis?

A

glutamine

66
Q

what enzyme converts glutamine to GABA?

A

Neuronal glutamic acid decarboxylase

67
Q

how are high affinity uptake systems important If transmembrane ion gradients break down under pathologic conditions (lack of oxygen enriched environements)?

A

they can work in reverse and glutamate toxicity can occur; Excessive accumulation of glutamate in the BECF –induced by ischemia, anoxia, hypogylcemia, or trauma- can lead to neural injury; sodium atpases are affected because ATP levels are low affecting sodium and potassium levels resulting in malfunctioning neurons

The inability of astrocytes to remove glutamate from the BECF under these pathologic conditions makes extracellular glutamate levels too high to become toxic for neurons

68
Q

what is the primary function of the oligodendrocytes in the CNS?

A

to provide and maintain myelin sheaths on axons, the myelin is the insulating electrical tape of the nervous system

69
Q

how many axons does the oligodendrocytes wrap around?

A

greater than a 1:1 ratio, Oligodendrocytes in white matter has 15 to 30 processes, each
connecting a myelin sheath to the oligodendrocyte’s cell body and each myelin sheath wraps around many times along the axon

70
Q

how is the schwann cell different from the oligodendrocyte?

A

In the Peripheral nervous system, a single Schwann cell provides a single myelin segment to a single axon of a myelinated nerve

The constituent proteins in PNS and CNS myelins are somewhat different

71
Q

what important enzyme can we find in the oligodendrocytes and the myelin?

A

enzyme carbonic anhydrase in the brain

which is important in CO2/HCO3- buffer system

72
Q

what is the effect of pH imbalance (acidity) in the brain vs seizures?

A

triggers seizure

73
Q

what other type of metabolism are oligodendrocytes involved with?

A

iron metabolism

74
Q

Microglial cells derive from these cells?

A

from cells related to the monocyte/macrophage lineage

75
Q

microglia represent what percent of the total glial cells within the CNS?

A

20%

76
Q

what activates the microglial cells?

A

activated by injury to the brain, proliferate and become phagocytic

77
Q

what are the most effective antigen presenting cells within the brain?

A

microglia

MABS Neuroscience (49 decks)

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