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54 Cards in this Set
- Front
- Back
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What are the 9 steps of neural differentiation?
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1. Neurulation
2. Regionalization 3. Neurogenesis 4. Migration 5. DIfferentiation 6. Apoptosis 7. Axon growth and guidance 8. Synapse formation 9. Synaptic rearrangement |
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What do the mesoderm and ectoderm give rise to?
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Endoderm gives rise to gastrointestinal tract and organs; mesoderm gives rise to muscles and bones
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What are the steps of neurulation?
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Neural plate ~ neural fold/grove + neural crests on the side ~ neural tube
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What is induction?
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Set of interactions whereby one causes the other to develop in a certain way
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Describe the organizer experiment.
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A portin of the mesoderm called "the organizer" normally gives rise to the notochord beneath the neural tube; Spemann and Mangold transplanted a second organizer into an embryo, which induced a second body axis, including the neural tube
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What did Spemann and Mangold do?
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Transplanted a secon dorganizer into an embryo, which developed a second obyd axis including hte neural tube
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Does the organizer belong to the ectoderm, the endoderm, or the mesoderm?
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Mesoderm
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What is the key concept of regionalization?
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Positional information
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What type of studies led to an understanding of positional information?
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Studies of how segments acquire distinct features in insects, hwereby the position of a cell in an animal determines its identity
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What is the chemical called that forms a gradient and determines which genes are activated?
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Morphogen
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What type of genes do morphogens usually affect?
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Transcription factors
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Describe how morphogens affect the pattern of the dorsal-ventral axis
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The notochord is the souce of morphogen; it secretes "sonice hedgehog' (SHH), from the ventral end of the spinal cord====== Others are elased from the dorsal end of the spinal cord.
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How is the anteriorposterior patterning of hte hindbrain estalibhsed?
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MOrphogens at the anterior and posterior ends activate transcription factors, such as "hox" nes that determine neuoranal identity
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What is the difference between the European plan and the AMerican plan of neurogenesis?
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European plan: what you become depends on who your parents are. American plan:who you become depends on your surroundings
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How/where do the principal neurons migrate?
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Migrate radially from the ventricular zone in the neural tube along radial glia; Interneurons migrate "tangentially" from subcortical areas
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Why do neurons have to migrate from the ventricular zone?
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Because most neurons are born in a small area inside the neural tube, called the ventircular zone
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What are neurons called undergoing their last mitosis?
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Vesicular cells
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Describe the inside-out birth order of neurons.
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Neurons are born deep in the ventricular zone, then migrate upwards; the first ones are deposited relatively deeply; the younger ones migrate past these older neurons and deposit past them, ending up in the cortical plate (these regions are called their laminar position)
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Why does timing five a predilection for stem cells to become certain neurons?
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The laminar position where these cells are deposited varies by time (it moves close to the cortical plate)
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What are the 4 defects in laminar position?
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1. Initiation defective (do not travel far enough)
2. Ongoing migration effects (mixed) 3. Lamination effect (not even) 4. Stop signal defective (too much integration |
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What are the 2 methods of differentiation?
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1. Dynamic polarization (axons and dendrites)
2. Choice of neurotransmitter |
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When does differentiation start?
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Starts during migration, but plays out one neurons are settled.
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In what excess are neurons generated?
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2-fold excess
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What part of the axon guides its growth?
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The growth cone
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Why is synaptic rearrangement counterintuitive?
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There is synaptic elimination; start with each axon making synapses to several mmature muscle fibers; in the end, a singl emotor axon innerveates a single muscle fiber
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Which of the nine steps in neural differentiation are ongoing?
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Neurogenesis and Apoptosis
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In which parts of the adult brain does neurogenesis continue at low levels?
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In the hippocampus and the olfactory bulb, but not the cortex
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What happens when the synaptic target of a neuronal type is removed during development? For example, if the target of motor neurons is removed, what happens?
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Neuronal death increases ~ cues presented by synaptic targets regulate neuron number
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What did Viktor Hamburger and Rita Levi-Montalcini do?
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Determined what it is about the target that causes them to die
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What is the trophic theory of neuronal survival?
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1. The target affects survival (not production or differentiation).
2. Neuron number is proportional to target size. 3. Hypothesis: Target secretes a limited amount of a "neurotrophic" molecule needed for neuronal survival, so when target is not there, it cannot secrete the "neurotrophic" molecule |
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What did "Tu" (the sarcoma tumor) show Hamburger and Levi-Montalcini?
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When sarcoma transplanted into chick embryo, axons from nearby ganglia grew into it ~ it was secreting an attracting, later found to be "nerve growth factor" (NGF)
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Describe how NGF prevents cell death.
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NGF binds to trkA, which activates Bcl-2 (regulator), which inhibits Apaf-1 (adapter). If it wasn't inhibited, Apaf-1 would be phosphorylated by ATP, which would activate Casp9 (EFfector), which would activate Casp3, which would cause cell death.
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How does the cell death program functions in C. elegans.
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NGF can activate Ced-9 *(regulator) which inhibits Ced-4 (adapter) which would otherwise activate Ced-3 (ffector), which causes cell death
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Is cell death a passaive process?
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No, it is an active program that is held in check by trophic factors
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When does most of the brain damage occur during a stroke?
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During the first 2-3 minutes, because it was during these 2-3 minutes that the apoptotic program was turned on when the brain lacked oxygen
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In the retinogeniculocortical pathway, where is hte first site of major convergence of inputs from both eyes?
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Projection of layer IV cells of V1 to cells in layer III of V1.
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Describe the distribution of cell constituents in precursorr cells of the developing neocortex.
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One end has Notch-1 and the other has Numb. Verticle division equally distributes them in daughter cell; horizontal does not; their different distributiosn give them different fates
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What are the sources of cortical cells?
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Prolferation of cortical pyramidal neurons and strocytes occurs in the ventricular zone of the dorsal telencephalon;inhibitory GABAergic interneurons and oligdendrocyt5es are generated in teh vetnricular zone of the ventral telencephalon, so they must migrate laterally over some distance to arrrive at their final destination in the cortex
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How do neuroblasts get to the cortical plate?
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Crawl from ventriclular zone up through subvetricular zone, through intermediate zone, to cortical plate via radial glia cells
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How many layers are there of the cortical plate (oldest closest to middle of brain)?
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6 layers
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How does a neuroblast become a pryamidal cell?
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Semaphorin 3A is secreted from the marginal zone, which attracts the growing apical dendrit and repels the growing axon (forces it in the other direction)
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What lamellipodia?
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Flat sheets along leading edge of growth cone; undulates in rhythmic waves
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WHat are filopodia?
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Thin spikes extending from lamellipodia, which constnatly problem teh environment, moving in and oout of the lamellipodia
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What is fasiculation?
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Bottom axon grows along the molecular highway of the exgtracellular mattrix by attaching with integrin molecules, while other axons (connected by CAMs to one another) 'piggy back'
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How do axons cross the midline of the spinal cord?
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Netrin is secreted by cellls in the ventral midline of spinal cord, which attracts axons with the appropriate receptors; slit is also secreted yb mdiline cells; axons that express the protein robo (the slit receptor) grow away from region of high slit concentration; once cross midline, there is an upregulation of robo, ensuring that the axons keep grwoing away from the midline
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What is retinotropy?
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Topographic organization of visual ptahways in which neighboring cells ont he retina send information ton eighboring cells ina target structure; nasal retina proejct to posterior tectuma dn temporal retinal project to anterior tectum (nasal have to cross over anterior to get to posterior
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Describe the retinotropy experiment in the frog.
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Membanes of cells from atnerior nad posterior tectum adn removed and deposited in striped pattern at boottom of Petri dish; experiments show tha tnasal retinal axons grow equally well on anterior and posterior; temporal are reppeld by membranes of posterior tectum and grow only on atnerior membranes
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How do CNS synapses form?
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Filopodium contact an axon, which leads to recruitment of synaptic vesicles and active zon eproetins; neurotransmitter receptors then accumulate postsynapticaly
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How are neuromuscular synapse formed?
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Growing motor neuron secrets agrin into basal lamina; interacts with MuSK in muscle cell membrane; causes rapsyn to cause clustering of ACh receptors in postsynaptic membrane
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Describe selective cell death.
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There are more input neurons than target neurons, so leads to cell death as a reult of hte limited quantities of trophic factors produced by target neurons
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Describe the formation of a Hebbian synapse.
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"Cells that fire together wire together;" two input neurson in one eye firse taht hte same tkime, which sufficient to cause the top LGN target neruon to fire, but not the bottom one, which causes synapses to undergo Hebbin modification and become more effective
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Describe teh dependence of plasticity of binoclular connections on modulatory inputs.
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Two modulatory inputs to the striate cortex (area 17) are from the basal forebrain complex (using ACh) and the locus operuleu (using NE); the activity obht is related to alevels fo attention adn laertness; if intact, monocular deprivation produces ocular dominance shift; ; if these inputs are cut, monocular deprivation has little effet on binocular connections in striate cortex)
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How might Hebbian modification be influenced by Ca2+?
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If glutamate released coincides with depolarziation sufficient to displace blocking Mg2+ ions, Ca2+ will ente the postsynaptic neuron via the NMDA receptor; Hebbian modification could be explained if hte Ca2+ admitted by teh NMDA receptor were to trigger enhanced synatpic efectiveness
(There are also AMPA receptors for glutamate, which let in Na+ to cause depolarization); LTP is associated with the insertion of AMPA recpetors into synapses that previously had none |
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What is the effect of closing one eye on AMPA receptors?
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Closing one eye replaces well correlated binocular activity with weak noise from one eye, which only weakly stimulates NMDA receptors, which causes internalization of AMPA receptors; oen the contrary, opening both tyese causes NMDA activation by well-correlated activity, which maintians AmPA receptors
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