Plasticity
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What is synaptic plasticity?
• a change in connection strength between a neuron and its target cell
What can synaptic plasticity lead to?
• changes in behaviour or changes in the response to sensory stimuli
What is sensitization?
• behavioural term describing an increased response to a stimulus • does not define a form of cellular change
A term describing a change in behaviour or response to a stimulus is not equal to?
• a mechanistic explanation for a cellular change
What happens when a repetitive stimulus is applied to a motor axon of a frog neuromuscular junction that is treated with curare?
• a series of action potentials occurs • curare blocks ACh which is quick to fill vesicles • initially APs get bigger (due to p) • Aps get smaller (n decreases as vesicles are used)
What happens when a repetitive stimulus is applied to a crayfish neuromuscular junction?
• low probability of release and naturally small epsp - continually increases
What is synaptic facilitation (paired-pulse facilitation)?
• rapid increase in synaptic strength that occurs when two or more action potentials invade the presynaptic terminal within ms of eachother
What happens when a pair of presynaptic action potentials elicits two epsps?
• the second ap has a greater amplitude • facilitation • due to an increase in p
What happens to facilitation when pairs of presynaptic aps are separated by varied time intervals?
• facilitation decreases in a decay timecourse • facilitation phase 1 • simplest forms of “memory” encoding
What does the decrease in variance/mean and increase in mean indicate?
• increased amplitude is compatible with an increased P
What is synaptic depression?
• nt release declines with sustained synaptic activity
At normal physiological levels, what happens when a squid axon is stimulated with high-frequency tetanus?
causes a depression of epsps
When the external calcium is lowered and the squid axon is stimulated with a high-frequency tetanus, what is observed?
• intermediate levels: reduces nt release, mixture of depression and augmentation • low levels: eliminates depression, leaving only augmentation
What does the change in depression with the change in calcium say about the mechanism of depression?
• it depends on the amount of nt released
What is post tetanic potentiation?
• when a train of high frequency stimuli is followed by enhancement lasting several minutes • because calcium has accumulated
What is the difference between augmentation and potentiation?
• both enhance the ability of incoming calcium to trigger fusion of synaptic vesicles (mechanisms not understood) • augmentation rises and falls over a few seconds • potentiation acts over a time scale of tens of seconds to minute
What are the four different forms of plasticity? How long do each of them last?
• facilitation (< 1 s) - 2 APs • augmentation (5-10 s) • post-tetanic potentiation (10s-mins) • depression (5-7 s)
Multiple activity dependent effects on transmitter release are overlaid at all synapses, the outcome depends on?
• duration of activity • time-course • relative magnitude of different forms of plasticity
What is habituation?
• a process that causes the animal to become less responsive to repeated occurrences of a stimulus
What is sensitization?
• a process that allows an animal to generalize an aversive response to non-noxious stimulus
Touching the siphon of an Alplysia causes what process?
• habituation - less gill withdrawal
After touching the siphon of an Alplysia to evoke habituation, what happens when the tail is shocked and the siphon is touched?
• dishabituation/short-term sensitization (sensitization would be if not habituated first) • more gill withdrawal
How long does short-term sensitization last?
~2 hours before becoming habituated again
What occurs if tail shocks and siphon touching are repeated multiple times?
• causes prolonged sensitization • lasts for days or weeks • simple long-term memory