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Flashcards in Module C Deck (111):
1

What layer of embryo does nervous system develop from?

Ectoderm

2

What triggers neural induction?

interaction with the mesoderm

3

What does the neural tube form from?

Neural plate

4

Function of BMP in early neurogenesis

Suppresses neural differentiation and promotes the
formation of epidermal tissue

5

What is the Function of Chordin and Noggin?

-Block the action of BMP
-allow for a selection of ectodermal cells to form the neural PLATE

6

Where do the signalling proteins Chordin and Noggin come frm?

Henson's node

7

At what time in embryogenesis does the neural plate form?

by 2 ½ weeks of development

8

Describe the development of neural tube.

1) Infolding of neural plate by changes in the shapes of
the cells of the neural ectoderm , pinching at apices and expanding their bases ( not increase in cell number)
2) beginning in the middle and moving both rostrally and caudally

9

A failure of the tube to close rostrally leads to ________

anencephaly (lack neocortex)

10

Failure of the tube to close caudally leads to _________

spina bifida (part of the meninges or spinal cord protrudes through the spinal column)

11

Where does the neural crest cells develop from?

pinches off from the margins of the neural groove as it closes to become the neural tube

12

What does the neural tube and neural crest cells form

Neurons and glial cells

13

What type of proteins do Homeobox genes encode?

Transcription factors

14

What part of the brain develop segmentally

Rhombencephalon aka hindbrain

15

What causes the segmentation in development of hindbrain

Several genes whose pattern of expression at early stages in development correlates with the segmental boundaries of the hindbrain

16

Where is the Homeobox located?

conserved stretch of DNA in Homeotic genes

17

What do Homeobox encode

encodes a sequence of 60 amino acids that recognize and bind to specific DNA sequences in a series of subordinate genes

18

Master control genes aka

Hox genes

19

Function of Hox genes in Vertebrate embryo

creating structures appropriate to a particular anterior-posterior position

20

_____ and _____ Hox genes in humans

emx and otx

21

Genetic abnormalities of emx develop _______

schizencephaly, (deep crevices in cortex)

22

Genetic defects in otx develop _______

epilepsy

23

what determines the pattern of Hox gene expression?

longitudinal gradient of retinoic acid

24

Where is Retinoic acid produced?

Henson's node

25

Henson's node equivalent in avian and mammalian embryos

Spemann organizer

26

How does retinoic acid effect Hox genes?

- activate transcription of Hox genes
- there are systematic differences in the sensitivity of different Hox genes to retinoic acid

27

How is the retinoic acid gradient established?

diffusion of retinoic acid from Hensen’s node establishes a gradient along the short length of the embryo

28

What is the floor plate?

a band of specialized cells, lies along the ventral midline of the spinal cord

29

Signals from the ______, induce ventral spinal cord characteristics

Notochord (lies ventral to neural tube)

30

Describe pattern established by notochord

- ventral midline of the spinal cord===> Floorplate
- Adjacent regions of the neural tube give rise to ===> motoneurons,
- more dorsal regions===> interneurons
- the most dorsal region===> neural crest

31

___________ protein produced by notochord to induce ventral development of neural tube

Sonic hedgehog

32

________ secreted by ectodermal cells dorsal to the developing spinal cord and it induces the specification of
cells that lie in the dorsal horn

BMP (yea really!!!)

33

Other groups of neurons induced by Sonic Hedge hog

- serotoninergic neurons in the anterior hindbrain,
- dopaminergic neurons in the posterior midbrain,
- oculomotor neurons in the anterior midbrain

34

Cells of the neural tube are oriented _______

Radially

35

Steps of cell proliferation.

1) Cell nucleus migrates to the tube’s inner or ventricular surface
2) The pial end of the cell detaches
3) The cell divides
4) The nuclei of the daughters migrate toward the outer surface as the cells reattach to that surface

36

How do neurons migrate?

along Radial Glia

37

Older cells are found closer to _________ surface

external or pial surface

38

Radial glia are brief lived during development but are still found in 2 locations in adults

1) adult retina as Muller cells
2) cerebellum as Bergman glia

39

What does Neuronal birthdating done with?

timed pulses of tritiated thymidine

40

Neuronal birthdating shows that the larger cells are _______

older

41

All neurons in the brain are born before birth with 2 exceptions:

1) Granule cells in the cerebellum
2)Olfactory neurons

42

Which proteins mediating neuronal migration along radial glia?

1)neural glycoprotein astrotactin
2) specific isoforms of the extracellular matrix adhesion molecule receptor integrin

43

How do GnRH neurons migrate into CNS?

Along axonal tracts;
moving from the olfactory pit, an ectodermal derivative (placode) that gives rise to the nasal
epithelium, into the hypothalamus

44

What causes Kallmann’s syndrome?

migration fails to occur during development as a result of malformation of the olfactory placode

45

Symptoms of Kallmann's syndrome?

no sense of smell and fail to mature sexually

46

Neural crest cells use neither Radial glia nor axonal tracts. How do they migrate?

along pathways marked by laminin

47

After migration, maturation of neuron depends on _________

its environment

48

What is Leukemia Inhibiting Factor (LIF)?

A peptide released by the muscle cells causes the change in phenotype of the crest cells and induces differentiation of cells in the immune system

49

What peptide induces differentiation of immune system?

LIF

50

Describe Axonal growth

1) The tip of the growing axon is enlarged to form the growth cone
2) It moves across and through the substrate, extending the fiber by adding membrane.
3) dynamic, interactive process in which projections from the growth cone (filopodia) extend and move to contact other cells and the substrate.
4) Receptors on the axon surface interact with specific molecules of the substrate.
5) In some cases growth cones may release enzymes to help clear a path and change the substrate.
6) Diffusible molecules released by cells along the pathway may also attract the growing axon

51

Axons that cross in the anterior commissure in the spinal cord are attracted there by a diffusible substance known as

Netrin

52

Netrin is released by

Floor plate

53

Molecule found in surrounding material that promotes neurite growth

Laminin

54

Where is Laminin found?

1) along pathways that axons follow as they extend
their processes in the developing nervous system
2) synthesized by Schwann cells after injury

55

Protein needed for layers of Schwann cell membranes to wrap and seal themselves around developing axons

PMP-22 (peripheral myelin protein)

56

In what hereditary disease is PMP-22 is not normal, peripheral myelin fails to form properly?

Charcot-Marie-Tooth disease

57

What is genetic defect in Charcot Marie Tooth Disease?

substitution of a glycine by aspartate

58

Formation of axon bundles is called

Fasciculation

59

What is responsible for fasicualtion

- Neural Cell Adhesion Molecules (N-CAMs) in the developing axons’ membranes
- binds to itself and thus causes axons to stick to one another

60

What is function of Agrin released by nerve cells that innervate the skeletal muscle ?

Receptors aggregate at the endplate, extrasynaptic sensitivity decreases

61

What happens to sensitivity after denervation?

-The sensitivity spreads again, but the focal sensitivity at the endplate and the acetylcholinesterase molecules located there are not lost

62

Role of Nerve Growth Factor in neuronal development

1) Enhance the outgrowth of neurites from sensory and sympathetic neurons (dorsal root ganglia)
2) essential for their survival as well.

63

Role of NGF in adult neurons

Regualtes synthesis of Norepi by inducing two enzymes required for its synthesis: tyrosine hydroxylase and
dopamine b-hydroxylase

64

How is NGF taken up by neurons?

retrograde transport from nerve terminals to the cell soma

65

Protein that is homologous to NGF that promotes the survival of dorsal root ganglion neurons and maintains CNS connections of sensory neurons

brain-derived neurotrophic factor (BDNF)

66

BNDF and NGF belong to what family of growth fatcors

neurotrophins

67

Basic structure of neurotrophins

dimers of a small basic peptide, held together by disulfide linkages between the conserved cysteine residues

68

Other neurotrophins

NT-3,NT-4/5, and NT-6

69

What neurotrophins are needed by neural crest cells and sensory neurons in dorsal root and trigeminal ganglia for proliferation, differentiation, and survival BEFORE they innervate targets?

BDNF or NT-3

70

What is the source of neurotrophins early in development?

neurons themselves and by the mesenchymal tissues through which the sensory axons grow

71

After sensory neurons reach their targets what is the source of NGF

Target cell produces NGF and neurons begin to express NGF receptors

72

What are the 2 types of neurotrophin receptors found on the surface of their target neurons?

1) low affinity (Kd = 10-9M) fast NGF receptor or p75
2)There are also high affinity (Kd = 10-11M) receptors

73

Where are the low affinity neurotrophin receptors found?

Both neurons and nonneuronal cells.

74

Where are the high affinity neurotrophin receptors found?

Only on Neurons

75

The high affinity receptor found on neurons is called

p140prototrk or simply trk ( produced by oncogenes)

76

Structure of trk

consists of:
- an extracellular domain with the neurotrophin-binding
site
- a short transmembrane segment,
- an intracellular domain encoding a tyrosine kinase

77

What are the 3 members of the trk family of proto-oncogenes?

1) Trk-A
2) Trk-B
3) Trk-C

78

Which neurotrophin is Trk- A a receptor for?

NGF

79

Which neurotrophin is Trk- B a receptor for?

BDNF and NT-4/5

80

Which neurotrophin is Trk- C a receptor for?

NT-3

81

What happens after binding of neurotrophin to its high affinity receptor?

1) an increase in tyrosine phosphorylation of the receptors themselves.
2)This activates three intracellular signaling pathways, phospholipase C, phosphatidylinositol-3-kinase, and the MAP kinase cascade.

82

How does low affinity receptor differ from High affinity receptor structurally?

lacks any intracellular domain

83

What is function of the low affinity receptor?

unknown
- may interact with the high affinity receptor during the binding of neurotrophins
- may trigger cell death, or provide a
mechanism for restricting diffusion and establishing high local concentrations
of neurotrophins, as during peripheral nerve regeneration.

84

Which areas of the CNS BDNF or NT-3 for survival?

Cells in the cortex and hippocampus
BNDF- retinal ganglion cell branching and remodeling,
dendritic growth of cortical neurons, and the formation of ocular dominance
columns in developing visual cortex

85

What is the hypothesis for apoptosis occurring during development?

Cells may be competing for vital substance released by the target

86

Polyneuronal innervation

During development muscle , which are singly innervated when mature , are innervated by multiple motoneurons until they are reduced by synapse elimination

87

Which cell mediates Reduction or elimination of polyneuronal innervation?

The muscle fiber

88

Other regions where Reduction of polyneuronal innervation occurs

Autonomic Nervous system and Cerebellum

89

Where do retinal ganglion cells grow towards

optic tectum

90

Ganglion cells from nasal retina innervate _________ tectum and cells from temporal retina innervate ________ tectum

posterior; anterior

91

What receptor is responsible for repulsive interaction of retinal ganglion cells?

Ephrin (Eph) receptor of tyrosine kinase receptors

92

What are the ligands expressed in tectum during formation of retinotectal connections?

Ephrin A-2 and Ephrin A-5

93

Concentration of Ephrin ligands is highest in _______ tectum and lowest in ________ tectum

posterior; anterior

94

__________ ganglion cells have highest ephrin receptors than __________ ganglion cells

Temporal ; Nasal

95

Matching of neurons to target is not rigid and can be changed by _________

experience after birth

96

Brodmann's area for primary visual cortex

Area 17

97

visual input goes into which layer

Layer 4

98

What does a plastic occluder do ?

allows light but no form or contrast to go through

99

Stribismus

congenital squint

100

When muscles are denervated they get ______(more or less) sensitive to transmitter

More (supersensitive)

101

Why can't CNS axons grow over long distances?

Partly due to proteins on surface of astrocytes and Oligodendrocytes that inhibit axon growth

102

Where is the primary and secondary effect of the drug thalidomide?

Primary- neurons
Secondary- bone growth=reduce appendages to flipper

103

What is the effect of albinism on neuronal development?

-alter axon growth and the formation of connections
-miswiring of retinogeniculate connections

104

What layer does notochord originate from?

mesoderm

105

What layer does neural plate, neural fold, neural tube and neural crest originate from?

ectoderm

106

Where would oldest neurons be found during development?

towards ventricular surface; young neurons pass by older ones

107

short range immobile factors promoting growth include

Laminin and NCAMs

108

Short range diffusible factors promoting growth include

Sonic hedgehog and netrin

109

Long range factors promoting growth include

NGF

110

immunosypathectomy caused by antibody to

NGF

111

What happens when one eye lid is closed immediately after birth?

shrinkage of columns supplied by that eye
failure of cortical cells to be driven by that eye
eventual blindness in that eye if lid not opened for more than 3 months