Specificity of Synapse Formation Flashcards
For what kind of synapse formation are critical periods important?
Activity-dependent synapse refinement (nurture).
What is the main relay for RGC projections in humans?
LGN.
True or false: some layers of the LGN receive inputs from both eyes and other layers inputs from one eye only.
False: every LGN layer receives inputs from one eye only.
How was the RGC-LGN pathway mapped?
Via transneuronal labeling with radioactive amino acids.
What inputs are receiving ocular dominance columns?
Inputs from the LGN from either the ipsilateral or contralateral eye.
Who is it that described the phenomenon of ocular dominance column formation?
Hubel and Wiesel.
During which period of development is the formation of ocular dominance columns principally occuring?
Critical period of the visual system.
Is the formation of ocular dominance columns dependent on exogenous activity? How was it demonstrated?
No, the formation of ocular dominance columns occurs priorly to eye-opening. By introducing an anterograde tracer into the LGN (monocular), Katz (2000) proved the existence of segregated columns.
If activity is not necessary for formation of ocular dominance columns, what is it useful for?
Maintenance and consolidation of ocular dominance columns.
What can be done experimentally to show that LGN layers sorting is dependent on endogenous spontaneous activity?
TTX injection prevents the formation of LGN layers before eye-opening.
How can waves of spontaneous activity in the LGN propagate so rapidly and synchronize whole neuronal bands?
Probably use gap junctions.
What is thought to happen at the level of the synapse during activity-dependent fine-tuning of synaptic connections in the visual system?
Connection refinement: neurons firing together are more likely to originate from the same eye and seek more neurotrophic factors.
True or false: early in development, each muscle fiber is innervated by one motor neuron, whereas later in dev., each muscle fiber is polyinnervated (2+ motor neurons).
False: the opposite.
How does the elimination of synapses occur at the NMJ?
Axons compete to innervate muscle fibers.
True or false: the more axons a neuron synapses with, the stronger the synapses.
False: the opposite.
When an axon retracts because its synapse is won over by another axon, what happens to the receptors that the synapse contains?
They are reused by the new winner axon.
What leads neuroscientists to hypothesize that elimination of synapses at the NMJ is more dependent on differential activity than presence of activity per se?
Complete block of activity at NMJ synapses does not change the morphology of innervation circuits. However, increasing differential activity of competing inputs by stimulating only certain parts of the innervation circuits lead to changes in morphology for the latter.
For refining NMJ circuits, is synchronous or asynchronous activity more applicable?
Asynchronous because synchronous activity does not heighten the competition.
What is the proposed mechanism for synapse elimination (loosing axons) at the NMJ?
Receptor activation probably leads to the release of a neurotrophic factor, protecting the active synaptic sites. Simultaneously, a destabilization signal is probably propagated to neighbouring synapses.
True or false: the winner is always the neuron with less connections already.
True.
True or false: not all motor neurons win the same number of competitions.
False: each motor neuron is generally winning the same number of competitions.
