Lecture 13: Early Brain Development Flashcards

(74 cards)

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
What happens to the anterior ends of the neural plate?
- AKA anterior neural folds - Grow together at midline - Continue to expand - Eventually gives rise to brain
26
What do stem cells of the neural tube ultimately give rise to?
- Entire brain - Spinal cord - Much of PNS
27
What do floorplate and roofplate signal?
- Stem cell differentiation of spinal cord/hidbrain development from neural tube
28
What does the neural crest give rise to?
- Neurons and glia of sensory and autonomic ganglia | - And other non-neuronal structures
29
How many migratory paths do neural crest cells have?
- 4
30
What do the different migratory paths of neural crest cells allow for?
- Distinct cellular environment interactions
31
What are the migratory paths that neural crest cells have?
- Sensory ganglia - Visceral motor (autonomic) ganglia - Adrenal neurosecretory precursor cells aggregate around dorsal kidney - Non-neuronal pigment, cartilage, bone (primarily of face/skull)
32
What happens after the formation of the neural tube?
- Major brain regions gradually begin to become apparent as differential growth causes bends/folds/constrictions of tube
33
What does the anterior end of the neural tube form?
- A crook | - Cephalic flexure
34
What does the cephalic flexure form?
- Balloons out - Forms prosencephalon - Gives rise to forebrain/cortex
35
What is the bulge that forms rostral to cephalic flexure and posterior to prosencephalon?
- Mesencephalon | - Gives rise to midbrain (substantia nigra and ventral tegmental area)
36
Where does the rhombencephalon form?
- Between cephalic flexure and caudal cervical flexure | - Gives rise to hindbrain
37
What does the neural tube caudal to the cervical flexure form?
- Spinal cord
38
What is the telencephalon? What aspects of the brain does it form?
- Lateral aspects of prosencephalon - Most rostral part - Cerebral cortex, hippocampus, basal ganglia, basal forebrain, olfactory bulb
39
What is the diencephalon and what does it form?
- Caudal portion of prosencephalon - Thalamus, hypothalamus, optic vesicles (neural retina) - Sensory processing
40
What is the mesencephalon and what does it consist of?
- Superior/inferior colliculi, midbrain tegmentum (including substantia nigra)
41
What is the metencephalon and what does it form?
- Rostral rhombencephalon | - Cerebellum, pons (of hindbrain)
42
What is the myencephalon and what does it become?
- Caudal rhombencephalon | - Medulla
43
What are neuromeres?
- Neural tube is organized into repeating units called neuromeres
44
What does the formation of neuromeres lead to?
- Segmentation | - Establish regional identity in body and possibly also brain
45
What are Hox genes responsible for?
- In hindbrain and spinal cord | - Guide differentiation of embryo into distinct segments
46
What are DLX and PAX genes and what are they responsible for?
- In midbrain and forebrain | - Guide differentiation of embryo into distinct segments
47
How many clusters of homologous genes for differentiation do flies have?
- One (on one chromosome)
48
How many clusters of homologous genes for differentiation do humans/other vertebrates have?
- 4
49
What does the pattern of Hox, DLX and PAX gene expression relate to?
- Formation of morphological features (shapes/bends/folds) that underlie progressive regionalization of developing neural tube
50
What is neural induction?
- 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
What happens when sections of developing embryo are cut out and transplanted to a different region?
- Acquired a new identity (influenced by local factors) OR - Retained original identity (influenced by original, immutable instructions)
52
How can interactions b/n cells influence cell fate?
- Points of communication - Local diffusible factors - Direct physical interactions b/n membrane proteins
53
Which structures produce molecular signals that induce cell/tissue differentiation?
- Embryonic notochord - Floorplate - Neural ectoderm - Somites
54
What are some results of inductive signalling?
- Change in gene expression, shape, and motility of target cells
55
What begins after the initial patterning of the neural tube is complete?
- Neurogenesis
56
What provides basic identities of precursor cells?
- Distinct signatures of gene expression
57
Where are precursor cells located?
- Ventricular zone | - Innermost cell layer surrounding lumen of neural tube (encapsulates ventricle)
58
What type of cell movements do precursor cells undergo? What does that lead to?
- Stereotyped pattern of cell movements | - Formation of new stem/precursor cells or neuroblasts (immature nerve cells)
59
Where is the nucleus located at the G1 growth stage?
- Cell body/nucleus is near ventricular surface
60
Where is the nucleus during the S/DNA synthesis stage?
- Nucleus migrates toward plial (outside) surface, DNA replicates
61
What happens during the G2 growth stage?
- Cell grows - Nucleus migrates toward lumenal (ventricular) surface, precursor cell loses connection to outer surface (localized to ventricular surface)
62
What are the 2 ways that neural precursor cells can divide in mitosis?
Symmetrical -> two neural stem cells | Asymmetrical -> postmitotic neuroblast and another progenitor cell (daughter/stem cell) that reenters cell growth cycle
63
The notochord forms which germ layer?
- Mesoderm
64
The hypothalamus arises from which primitive brain region?
- Diencephalon
65
What is the main excitatory neurotransmitter in the adult brain?
- Glutamate
66
The primary transmitter released by the medium spiny neurons of the striatum is...
- GABA
67
Most neuroblasts that migrate long distances in CNS use what to guide them?
- Radial glial cells | - These are progenitor cells that can become neuronal progenitor cells, oligodendrocytes, and astrocytes
68
Where do postmitotic neurons move past? How?
- 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
What is gastrulation?
- Days 13-19 | - Movement of cells toward midline then forward along midline forming primitive streak
70
What is the end result of gastrulation?
- Formation of ectoderm, endoderm and mesoderm
71
As ectoderm thickens, what does it become?
- Neural plate
72
What does the fluid filled inside of the neural tube become?
- Cerebral ventricles - Central canal - Connections between
73
How long does it take for prosencephalon, mesencephalon and rhombencephalon to become distinct?
- 24 days
74
What are the stages of neural development?
- Neurogenesis - Neural migration - Differentiation - Process outgrowth - Synaptogenesis