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Nervous System: Unit I > Embryology II-IV > Flashcards

Embryology II-IV Flashcards

1
Q

Location of neurogenesis

A
  • ventricular zones = layers closes to the ventricles @ brain/central canal @ spinal cord
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2
Q

General process of neurogenesis

A
  • neurectoderm ==> neural tube ==> begining of neurogenesis (Day 22)
    • most neurogenesis is embryonic, but some postnatal
  • precursors @ different regions in CNS behave differently ==> patterning events
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3
Q

Neurogenesis definition

A
  • =process of generating neural cells
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4
Q

Nucleaur positioning during cell cycle of neuronal precursors

A
  • dividing cells have processes that attach medially to the ventricular surface & laterally to external surface
  • position of nucleus changes as cell continues through cell cycle
    • @ S = most superficial
    • @ M = most deep
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5
Q

Common methods used to study neurogenesis

A
  • label dividing cells w/detectable DNA precursors
    • cells take up labled precursors during S phase
    • label allows tracking of cells and progeny
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6
Q

“Cell birthdate” definition

A
  • =time a cell finishes l_ast round of DNA synthesis_ ==> divides ==> exits cell cycle from M phase
  • after cell birthdate ==> neuronal differentiation begins
  • cells with similar birthdays end up in the same layer ==> time when a neuron is born has a big impact on its fate
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7
Q

Secondary zones of neurogenesis definition/examples

A
  • =brain regions that undergo postnatal neurogenesis
  • cerebellum: granule neurons
    • external granule layer
  • oflactory neurons
    • subventricular zone ==> olfactory bulb neurons
  • hippocampal neurons
    • dentate gyrus
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8
Q

Formation of cerebellar granule neurons

A
  • precursors @ rim of 4th ventricle ==> migrate while still dividing ==>
  • new neurogenic region = “external granule layer”
  • granule cell progenitors proliferate ==> “born” ==> migrate to cerebellum
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9
Q

Shared characteristics of cells in secondary zones of neurogenesis

A
  1. arise in ventricular zone
  2. migrate before exiting mitotic cycle to new, non-ventricular location
  3. proliferate postnatally @ non-ventricular location
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10
Q

Adult neurogenesis

A
  • neurogenesis in adults @:
    • dentate gyrus
    • subventricular zone
  • also cell death occuring ==> no total increase in neurons
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11
Q

Perpendiciular vs. parallel progenitor cell division

A
  • perpendicular = plane of division is perpendicular to ventricular surface
    • both daughter cells remain attached to ventricular surface
    • majority of these cells remain in cell cycle
  • parallel = plane of division is parallel to ventricular surface
    • one daughter cell attached to ventricular surface and one is not
    • “assymetric division”
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12
Q

Characteristics of assymetric division

A
  • parallel division ==> one unattached daughter cell
  • unattached cell ==> begins differentiation
  • plane of cleavage may impact inheritance of various factors (e.g. proteins, mRNAs)
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13
Q

Preplate definition and division

A
  • cerebral cortex region formed by first postmitotic, migrating neurons
  • divides into (from superficial ==> deep): marginal zone, cortical plate, the subplate, intermediate zone, and deep ventricular zone
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14
Q

Subplate characteristics

A
  • formed from division of preplate
  • neurons @ SP = earliest born & are “poineers” of circuit formation
  • many neurons die early after completing role
  • ~transient neuronal population
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15
Q

Glial role in neuronal migration

A
  • radial glia extend from ventricle to surface
  • neurons use glia as “guides” during migration
  • wave of neurogenesis finishes ==> neurons migrate into cortical plate via radial glia
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16
Q

Pattern of neuronal migration into cerebral cortex

A
  • “inside-out” pattern
  • neurons born later migrate past first-born neurons
  • first-born neurons = closest to ventricular surface
  • later-born = closest to pial surface
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17
Q

Stages of neuronal migration @ cerebral cortex

A
  1. onset of migration
    1. starting of migration
    2. involves modulation of actin cytoskeleton in order to initiate
  2. ongoing migration
    1. continued migration along radial glia past earlier-born neurons w/recognition of distinct layers
  3. migration stop
    1. recognition of appropriate layer and disengagement from radial glia
    2. Reelin proposed as involved
18
Q

FLNA gene characteristics

A
  • FLNA = filaminA ==> actin-binding crosslinking protein
  • defects in FLNA lead to inability to initiate neuronal migration ==> periventricular heterotopia
19
Q

LIS1 gene characteristics

A
  • LIS1 believed to produce a protein that regulate microtubular cytoskeleton fxn associated w/nuclear movement
  • defect impacts ongoing neuronal migration and leads to Type I lissencephaly
    • neurons begin migration but do not make it to cortical plate
20
Q

DCX gene characteristics

A
  • Neurons express DCX as they migrate ==> believe to regulate microtubular cytoskeleton
  • defect impacts ongoing neuronal migration ==> double cortex syndrome
21
Q

Reeler gene characteristics & associated genes

A
  • [in mice] reeler encodes reelin protein = large extracellular protein
    • expressed by Cajal-Retzius cells @ marginal zone and preplate
  • defect leads to problems stopping neuronal migration ==> inverted inside-out pattern
  • Vldlr & Apoer2 = cerebbelar & cerebral reelin receptors
  • Dab1 = intracell protein in reelin signal transduction
22
Q

Retinal pattern of neural migration

A
  • reversed compared to cerebral cortex
  • follows an “outside-in” order
  • ganglion cells are born first and photoreceptors are born last
23
Q

Radial migration definition + cell types

A
  • = migration along radial glia
    • accounts for most of migration
  • cells: many of cerebral cortex undergo radial migration
    • Glutamate-containing neurons (pyramidal cells)
24
Q

Tangential migration definition + cell types

A
  • tangential migration ==> cells dispersed through developing tissue
  • cells: inhibitory GABA-containng cells in cerebral cortex
    • migrate from lateral/medial ganglionic eminences
25
Q

Chain migration definition + cell types

A
  • = neuronal precursors move as chains along the rostral migratory stream pathway
  • neurons from the subventricular zone near lateral ventricle ==> olfactory bulb
26
Q

Neural crest orgin and future structures

A
  • neural crest = mass of cells on top of dorsal tube between the neuroectoderm and epidermis
  • neural crest cells ==> peripheral nervous system + variety of other cell types
27
Q

Neural crest migration vs. Radial migration

A
  • neural crest cells migrate fast, w/out guiding cells
  • express integrins = receptors for laminin and fibronectin @ ECM
  • fate influenced by rostro-caudal position prior to migration
  • migratory patterns:
    • dorsal stream => pigment cells
    • ventral stream => sensory, autonomic, and enteric ganglia
28
Q

Apoptosis vs. Necrosis

A
  • necrosis: response to extreme physio conditions ==> death of cells via loss of membrane integrity
    • associated w/trauma or external injury
  • apoptosis: occurs under normal physio conditions and cell actively participates in own demise
    • involved in development
29
Q

Timing & purpose of cell death w/in nervous system development

A
  • purpose: pattern formation, brian morphogenesis, removal of unnec. neurons, etc.
  • timing: coincident w/establishment of connection by a particular neuronal population
30
Q

Neurotrophic hypothesis

A
  • targets provide limiting amounts of nutrient (trophic factor) taken up by input nerve terminals
  • determines how many neurons die/survive at post-synaptic organs
31
Q

Neurotrophic factors/neurotrophis definition

A
  • molecules released by targets that promote cell survival
    • inhibit apoptosis
  • neurotrophins = family of related proteins
    • NGF (nerve growth factor)
    • BDNF (brain-derived neurotrophic)
    • NT-3 (neurotrophin-3)
    • NT-4/5
  • also regulate neuronal development and function
32
Q

Examples of long-range (diffusible) axon guidance molecules

A
  • attractive
    • netrins
  • repulsive
    • semaphorins, netrins
33
Q

Examples of short-range (contact-dependent) axon guidance molecules

A
  • attractive
    • cell surface: cadherins, CAMs
    • ECM: collagen, laminin, fibronectin, proteoglycans
  • repulsive
    • cell surface: semaphorins, ephrins
    • ECM: tenascin
34
Q

Factors that impact axonal regeneration

A
  • ability of axons to grow
    • CNS axons can regenerate long distance
  • growth-promoting molecules
    • glial environment (e.g. Schwann cell) may produce NGF/other trophic factors
    • fibroblast growth factor (FGF)
  • molecules/receptors that inhibit growth
    • CNS myelin expresses molecule that prevents axonal regeneration (Nogo)
35
Q

Synapse elimination definition + timing/location

A
  • initial excess of neurons contacting cells ==> eliminate synapses via a competitive process = selective synapse elimination
    • _​_e.g. muscles during embryonic/early postnatal life = polyneuronal innervation ==> single neuron innervates
    • also occurs @ CNS; e.g. cerebellum @ purkinje cells; visual & auditory systems
36
Q

Mechanism of synaptic elimination

A
  • electrical activity helps facilitate synapse elimination
  • correllated firing of pre and post-synaptic = synpase stabilization
    • vs. uncorrelated promotes elimination
  • once activated, post-synaptic cell often releases neurotrophin/growth factor
37
Q

Postnatal changes in brain morphology

A
  • @ birth: low density of neural connections
  • ==> increase in size of soma and interconnections between neurons
38
Q

ASD and postnatal brain morphology

A
  • ASD brains ==> abnormally high increases in size (especially in white matter areas)
  • smaller neuronal cell bodies and fewer branching of dendrites
39
Q

Down’s Syndrome and postnatal brain morphology

A
  • dendritic abnormalities = abnormally thin and short
40
Q

Timing of myelination development

A
  • begins during embryonic stages
    • present first @ periphery
  • @ CNS:
    • myelination @ spinal cord near the end of the first trimester
    • myelination @ brain by end of third trimester
  • myelination @ some higher fxn cortical tracts occurs after birth
41
Q

Regulation of GABA receptors during development

A
  • GABA receptors = several types of subunits
    • some dominate during embryonic stages and some during adulthood
  • GABA receptors = inhibitory @ adult, but = excitatory in utero
    • excess intracell Cl- ==> ECl = depolarizing

Nervous System: Unit I (16 decks)

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