Specificity of Synapse Formation

Question 1

For what kind of synapse formation are critical periods important?

Answer 1

Activity-dependent synapse refinement (nurture).

Question 2

What is the main relay for RGC projections in humans?

Answer 2

LGN.

Question 3

True or false: some layers of the LGN receive inputs from both eyes and other layers inputs from one eye only.

Answer 3

False: every LGN layer receives inputs from one eye only.

Question 4

How was the RGC-LGN pathway mapped?

Answer 4

Via transneuronal labeling with radioactive amino acids.

Question 5

What inputs are receiving ocular dominance columns?

Answer 5

Inputs from the LGN from either the ipsilateral or contralateral eye.

Question 6

Who is it that described the phenomenon of ocular dominance column formation?

Answer 6

Hubel and Wiesel.

Question 7

During which period of development is the formation of ocular dominance columns principally occuring?

Answer 7

Critical period of the visual system.

Question 8

Is the formation of ocular dominance columns dependent on exogenous activity? How was it demonstrated?

Answer 8

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.

Question 9

If activity is not necessary for formation of ocular dominance columns, what is it useful for?

Answer 9

Maintenance and consolidation of ocular dominance columns.

Question 10

What can be done experimentally to show that LGN layers sorting is dependent on endogenous spontaneous activity?

Answer 10

TTX injection prevents the formation of LGN layers before eye-opening.

Question 11

How can waves of spontaneous activity in the LGN propagate so rapidly and synchronize whole neuronal bands?

Answer 11

Probably use gap junctions.

Question 12

What is thought to happen at the level of the synapse during activity-dependent fine-tuning of synaptic connections in the visual system?

Answer 12

Connection refinement: neurons firing together are more likely to originate from the same eye and seek more neurotrophic factors.

Question 13

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).

Answer 13

False: the opposite.

Question 14

How does the elimination of synapses occur at the NMJ?

Answer 14

Axons compete to innervate muscle fibers.

Question 15

True or false: the more axons a neuron synapses with, the stronger the synapses.

Answer 15

False: the opposite.

Question 16

When an axon retracts because its synapse is won over by another axon, what happens to the receptors that the synapse contains?

Answer 16

They are reused by the new winner axon.

Question 17

What leads neuroscientists to hypothesize that elimination of synapses at the NMJ is more dependent on differential activity than presence of activity per se?

Answer 17

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.

Question 18

For refining NMJ circuits, is synchronous or asynchronous activity more applicable?

Answer 18

Asynchronous because synchronous activity does not heighten the competition.

Question 19

What is the proposed mechanism for synapse elimination (loosing axons) at the NMJ?

Answer 19

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.

Question 20

True or false: the winner is always the neuron with less connections already.

Answer 20

True.

Question 21

True or false: not all motor neurons win the same number of competitions.

Answer 21

False: each motor neuron is generally winning the same number of competitions.