CSB332H1 Lecture Notes - Lecture 11: Synaptic Plasticity, Synaptic Vesicle, Chemical Synapse
14 May 2018
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Lecture 11(a): Altering Synapses I
Synaptic Plasticity:
1. Short-term Changes:
o Short-term synaptic plasticity lasts seconds to minutes
2. Long-term Changes:
o Long-term synaptic plasticity can last hours or days
ð The key characteristic of synaptic plasticity is that:
o The change in the strength of the synapse persists AFTER the activity that induced
the plasticity has ceased
(i.e. train of APs lead to a synaptic change; when train of AP ends, change persists)
• Changes in presynaptic electrical activity (APs) can alter synaptic efficacy
o Brief trains of APs can cause either an increase (facilitation) or a decrease
(depression) in the size of the
postsynaptic potential
(either an EPSPs or IPSPs)
Augmentation:
• Slower phase than facilitation
o Response is bigger and lasts longer (several seconds)
when compared to facilitation
Synaptic Depression:
• After high trains of activity there can be a reduction in
neurotransmitter release – can be due to the fact that when
this neuron when Ca2+ influx the amount of neurotransmitter
is depleted – get depressed
o Depression is often observed by tetanus
ð Tetanus is a prolonged (high) frequency of action potentials; stimulating a neuron very
frequently – neurotransmitter is not released effectively (less) for a short duration of time
o Depression is often followed after a few seconds by an increase in synaptic
potential; this is known as post-tetanic potentiation (PTP)
Facilitation & Depression:
• Facilitation is due to an increase in the mean number of quanta released by the presynaptic
nerve terminal
o # of quanta released is due to high residual Ca2+ left in the presynaptic terminal
• Depression is due to the depletion of neurotransmitter vesicle release by the presynaptic
nerve terminal
o # of vesicles is decreased often because neurotransmitters cannot be filled in vesicles
fast enough due to condition train of APs (i.e. tetanus; high frequency of AP)
ð Neurotransmitter released is subject to 2-short modifications: Facilitation & Depression
o It is often associated that one group of neurons experience one or the other
