24.6 Neuronal Plasticity Flashcards
What is the definition of neuronal plasticity?
The ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganising its structure, functions, or connections
What are the two main mechanisms of neuronal plasticity?
Synaptic reinforcement
Synaptic rearrangement
What is the rhyme that indicates the weakening of synaptic connections (long-term depression, LTD)?
Neurons that fire out of sync lose their link
What is the general mechanism of weakening synapses (LTD)?
When the presynaptic axon is active and the postsynaptic axons is simultaneously weakly activated by OTHER inputs - the synapse is weakened
What are the molecular mechanisms of LTD?
- Weak coincidences signalled by lower levels of NMDA receptor activation - less Ca2+ influx
- Triggers loss of AMPA receptors
- Long-term: loss of whole synapse
What is the critical period of plasticity?
The time in early postnatal life when the plasticity of the brain is strongly dependent on experience or environmental influences
What provides the greatest effects to neuronal plasticity?
really the long-term potentiation and depression of selected synapses
How is LTP generated via NMDA receptors?
NMDA Rs take longer than AMPA to open, but they cause greater depolarisation and are also associated with an influx of Ca2+.
*Ca2+ influx –> 2nd messenger:
- Insertion of more AMPA receptors into membrane OR phosphorylation of AMPA receptors (to make more effective)
- Formation of new dendritic spines to make new synaptic contacts (increases probability that AP will trigger glutamate release)
*More likely to fire together and wire together.
What are the different types of developmental plasticity?
cell birth
neurogenesis
gliogenesis
migration
differentiation
maturation
axonal and dendritic growth
synaptogenesis and pruning
myelogenesis
What are the two requirements for LTP to occur?
1) Synapses are stimulated at frequencies high enough to cause temporal summation of the EPSPs
2) Enough synapses must be active simultaneously to cause significant spatial summation of EPSPs
What are the two events that must occur for an NMDA receptor to conduct Ca2+?
- Glutamate binds
- Postsynaptic membrane is depolarised enough to displace Mg2+ that clog the channel
Describe the 1960s Hubel and Wiesel experiment of monocular deprivation that led to an understanding of visual critical periods
Suturing shut lids of one eye causes functional blindness in that eye, despite the fact that the retina of the deprived eye works fine after re-opening the eyelids
What is the function of LTD in the cerebellum?
Reports motor error
So ‘teaches’ Purkinje cells to which parallel fibres they should be less responsive
Major control of cerebellum-dependent motor learning
What is the role of neuronal plasticity in learning?
*Memory formation
*Skill acquisition
*adaptation to new information (reorganisation allows for integration of new info and for modification to existing knowledge)
