lecture 9- Synaptic function - synaptic plasticity Flashcards
Early theories of cellular mechanisms of memory
- Santiago Ramón y Cajal (1894)
Donald Hebb: The Organisation of Behavior (1949)
Santiago Ramón y Cajal (1894
Memories might be formed by strengthening of connections between neurons.
Donald Hebb: The Organisation of Behavior (1949)
Hebbian theory or “Hebb’s Law”
“When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased.”
Hebbian theory
starts of as a weak connection between A and B… then …
synaptic plasticity
- The strength of synaptic communication between two neurons is not fixed.
-Synaptic plasticity is a change in the strength of synaptic communication.
The first description of long-term potentiation (LTP) of synaptic strength
Measuring changes to synaptic strength:
long-term potentiation (LTP) - low
Measuring changes to synaptic strength:
long-term potentiation (LTP) - high
Does the high frequency stimulation paradigm obey Hebb’s law?
“Neurons that fire together, wire together”
General properties of LTP
- Input specificity
- Associativity
- Cooperativity
- Persistence
Input specificity
Associativity
- A weak stimulus in one pathway is not sufficient to elicit LTP.
- When paired with activity in another strong pathway -> LTP in both pathways.
Cooperativity
- A weak stimulus in one pathway is not sufficient to elicit LTP.
When paired with activity in another strong pathway -> LTP in both pathways. - Cooperativity is very similar to associativity but does not require the second pathway to have a strong stimulus just several input pathways activated at the same time.
Persistence
Mechanism of LTP induction
NMDA receptors are activated at depolarised potentials
In this context NMDA receptors are ‘coincidence detectors’:
They can detect presynaptic activity (glutamate)…
and postsynaptic activity (depolarisation) at the same time.
Why does NMDA receptor activation lead to LTP?
Ca2+ as a signalling molecule
Influx of Ca2+ ions activates intracellular signalling cascades
Potential mechanisms by which LTP is expressed
Long-term depression (LTD)
Found at many synapses in the brain, including in the hippocampus.
First described at parallel fibre-Purkinje cell synapse in the cerebellum.
Some forms of LTD are dependent on NMDA receptor activation
Some forms of LTD are dependent on NMDA receptor activation and postsynaptic Ca2+ entry
