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NEUR 2000 > Lecture 13: Early Brain Development > Flashcards

Lecture 13: Early Brain Development Flashcards

1
Q

What is gastrulation? When does it occur?

A
  • Establishment of basic body axes
  • Development of 3 embryonic germ cell layers from blastocyst
  • Very soon after conception
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2
Q

What are the basic body axes?

A

Anterior-Posterior, Dorsal-Ventral, Medial-Lateral

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3
Q

What are the 3 embryonic germ cell layers?

A
  • Ectoderm
  • Mesoderm
  • Endoderm
  • Gives rise to specific sets of tissues or organs in the body
  • Named for their relative position
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4
Q

Describe the ectoderm?

A
  • Outer layer of tissue

- E.g. nervous system, skin

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5
Q

Describe the mesoderm?

A
  • Middle layer of tissue
  • E.g. blood vessels, kidneys
  • Initiates the invagination that defines gastrulation
  • Fold becomes neural tube
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6
Q

Describe the endoderm?

A
  • Inner layer of tissue

- E.g. lining of lungs, liver

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7
Q

Where is the notochord formed?

A
  • Midline of the gastrulating embryo
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8
Q

What is the notochord?

A
  • Cylinder of mesodermal cells generated at the site of the surface indentation (primitive pit) that eventually elongates (primitive streak)
  • This is the start of invagination
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9
Q

What does the notochord define?

A
  • Embryonic midline and axis of symmetry for the body
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10
Q

Is the notochord permanent?

A
  • No, it is transient

- Disappears following early development

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11
Q

Where does the notochord send inductive signals to? What is the result?

A
  • Overlaying ectoderm

- Starts formation of nervous system

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12
Q

What is the neuroectoderm and what does it do?

A
  • Ectoderm immediately dorsal to notochord

- Gives rise to entire nervous system

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13
Q

What leads to differentiation of cells into neuroectodermal precursor cells?

A
  • Inductive signals from notochord trigger neuroectoderm
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14
Q

What forms the neural plate?

A
  • Neuroectodermal precursor cells thicken into neural plate
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15
Q

What happens in neurulation?

A
  • Lateral margins of neural plate (alar plate) fold inward

- Neural plate becomes neural groove that become neural tube

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16
Q

Is the neural tube homogenous?

A
  • No
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17
Q

What are 2 main structures of neural tube?

A
  • Floorplate

- Neural crest

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18
Q

Describe the floorplate?

A
  • Cells at ventral portion form floorplate
  • Specialized strip of epithelial-like cells
  • Provide inductive signals for neuroectodermal precursors of spinal cord and hindbrain
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19
Q

Describe the neural crest?

A
  • Emerges at lateral margins of neural plate

- ‘tips’

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20
Q

How do you know the neural tube is complete?

A
  • Edges of neural plate meet at midline, then neural tube is complete
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21
Q

What does the neural crest become?

A
  • Sensory and autonomic ganglia

- Peripheral nervous system

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22
Q

What does the mesoderm adjacent to the neural tube become?

A
  • Thickens and subdivides into somites (precursors of skeleton and muscle)
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23
Q

What does the neural tube adjacent to somites become?

A
  • Rudimentary spinal cord
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24
Q

What does the fluid-filled cavity of the neural tube become?

A
  • The ventricular system
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25
Q

What happens to the anterior ends of the neural plate?

A
  • AKA anterior neural folds
  • Grow together at midline
  • Continue to expand
  • Eventually gives rise to brain
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26
Q

What do stem cells of the neural tube ultimately give rise to?

A
  • Entire brain
  • Spinal cord
  • Much of PNS
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27
Q

What do floorplate and roofplate signal?

A
  • Stem cell differentiation of spinal cord/hidbrain development from neural tube
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28
Q

What does the neural crest give rise to?

A
  • Neurons and glia of sensory and autonomic ganglia

- And other non-neuronal structures

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29
Q

How many migratory paths do neural crest cells have?

A
  • 4
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30
Q

What do the different migratory paths of neural crest cells allow for?

A
  • Distinct cellular environment interactions
31
Q

What are the migratory paths that neural crest cells have?

A
  • Sensory ganglia
  • Visceral motor (autonomic) ganglia
  • Adrenal neurosecretory precursor cells aggregate around dorsal kidney
  • Non-neuronal pigment, cartilage, bone (primarily of face/skull)
32
Q

What happens after the formation of the neural tube?

A
  • Major brain regions gradually begin to become apparent as differential growth causes bends/folds/constrictions of tube
33
Q

What does the anterior end of the neural tube form?

A
  • A crook

- Cephalic flexure

34
Q

What does the cephalic flexure form?

A
  • Balloons out
  • Forms prosencephalon
  • Gives rise to forebrain/cortex
35
Q

What is the bulge that forms rostral to cephalic flexure and posterior to prosencephalon?

A
  • Mesencephalon

- Gives rise to midbrain (substantia nigra and ventral tegmental area)

36
Q

Where does the rhombencephalon form?

A
  • Between cephalic flexure and caudal cervical flexure

- Gives rise to hindbrain

37
Q

What does the neural tube caudal to the cervical flexure form?

A
  • Spinal cord
38
Q

What is the telencephalon? What aspects of the brain does it form?

A
  • Lateral aspects of prosencephalon
  • Most rostral part
  • Cerebral cortex, hippocampus, basal ganglia, basal forebrain, olfactory bulb
39
Q

What is the diencephalon and what does it form?

A
  • Caudal portion of prosencephalon
  • Thalamus, hypothalamus, optic vesicles (neural retina)
  • Sensory processing
40
Q

What is the mesencephalon and what does it consist of?

A
  • Superior/inferior colliculi, midbrain tegmentum (including substantia nigra)
41
Q

What is the metencephalon and what does it form?

A
  • Rostral rhombencephalon

- Cerebellum, pons (of hindbrain)

42
Q

What is the myencephalon and what does it become?

A
  • Caudal rhombencephalon

- Medulla

43
Q

What are neuromeres?

A
  • Neural tube is organized into repeating units called neuromeres
44
Q

What does the formation of neuromeres lead to?

A
  • Segmentation

- Establish regional identity in body and possibly also brain

45
Q

What are Hox genes responsible for?

A
  • In hindbrain and spinal cord

- Guide differentiation of embryo into distinct segments

46
Q

What are DLX and PAX genes and what are they responsible for?

A
  • In midbrain and forebrain

- Guide differentiation of embryo into distinct segments

47
Q

How many clusters of homologous genes for differentiation do flies have?

A
  • One (on one chromosome)
48
Q

How many clusters of homologous genes for differentiation do humans/other vertebrates have?

A
  • 4
49
Q

What does the pattern of Hox, DLX and PAX gene expression relate to?

A
  • Formation of morphological features (shapes/bends/folds) that underlie progressive regionalization of developing neural tube
50
Q

What is neural induction?

A
  • Instructions that establish stem cell capacity to make nerve cells specific to each region
  • Produce molecular signals that induce cell/tissue differentiation in vertebrate embryo
51
Q

What happens when sections of developing embryo are cut out and transplanted to a different region?

A
  • Acquired a new identity (influenced by local factors)
    OR
  • Retained original identity (influenced by original, immutable instructions)
52
Q

How can interactions b/n cells influence cell fate?

A
  • Points of communication
  • Local diffusible factors
  • Direct physical interactions b/n membrane proteins
53
Q

Which structures produce molecular signals that induce cell/tissue differentiation?

A
  • Embryonic notochord
  • Floorplate
  • Neural ectoderm
  • Somites
54
Q

What are some results of inductive signalling?

A
  • Change in gene expression, shape, and motility of target cells
55
Q

What begins after the initial patterning of the neural tube is complete?

A
  • Neurogenesis
56
Q

What provides basic identities of precursor cells?

A
  • Distinct signatures of gene expression
57
Q

Where are precursor cells located?

A
  • Ventricular zone

- Innermost cell layer surrounding lumen of neural tube (encapsulates ventricle)

58
Q

What type of cell movements do precursor cells undergo? What does that lead to?

A
  • Stereotyped pattern of cell movements

- Formation of new stem/precursor cells or neuroblasts (immature nerve cells)

59
Q

Where is the nucleus located at the G1 growth stage?

A
  • Cell body/nucleus is near ventricular surface
60
Q

Where is the nucleus during the S/DNA synthesis stage?

A
  • Nucleus migrates toward plial (outside) surface, DNA replicates
61
Q

What happens during the G2 growth stage?

A
  • Cell grows
  • Nucleus migrates toward lumenal (ventricular) surface, precursor cell loses connection to outer surface (localized to ventricular surface)
62
Q

What are the 2 ways that neural precursor cells can divide in mitosis?

A

Symmetrical -> two neural stem cells

Asymmetrical -> postmitotic neuroblast and another progenitor cell (daughter/stem cell) that reenters cell growth cycle

63
Q

The notochord forms which germ layer?

A
  • Mesoderm
64
Q

The hypothalamus arises from which primitive brain region?

A
  • Diencephalon
65
Q

What is the main excitatory neurotransmitter in the adult brain?

A
  • Glutamate
66
Q

The primary transmitter released by the medium spiny neurons of the striatum is…

A
  • GABA
67
Q

Most neuroblasts that migrate long distances in CNS use what to guide them?

A
  • Radial glial cells

- These are progenitor cells that can become neuronal progenitor cells, oligodendrocytes, and astrocytes

68
Q

Where do postmitotic neurons move past? How?

A
  • ## Postmitotic neurons adhere to glial process to move beyond dividing cells in ventricular and subventricular zones and past already-differentiating neurons in lower cortical layers of brian structures that express layered structure
69
Q

What is gastrulation?

A
  • Days 13-19

- Movement of cells toward midline then forward along midline forming primitive streak

70
Q

What is the end result of gastrulation?

A
  • Formation of ectoderm, endoderm and mesoderm
71
Q

As ectoderm thickens, what does it become?

A
  • Neural plate
72
Q

What does the fluid filled inside of the neural tube become?

A
  • Cerebral ventricles
  • Central canal
  • Connections between
73
Q

How long does it take for prosencephalon, mesencephalon and rhombencephalon to become distinct?

A
  • 24 days
74
Q

What are the stages of neural development?

A
  • Neurogenesis
  • Neural migration
  • Differentiation
  • Process outgrowth
  • Synaptogenesis

NEUR 2000 (10 decks)

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