Cell Bio 2 Exam 2 L22: Neural Plasticity 1
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define synaptic efficacy
the efficiency with which a signal is transferred from the presynaptic to the postsynaptic neuron
An increase in synaptic efficacy occurs when the presynaptic cell repeatedly and persistently stimulates the postsynaptic cell
lasting cellular changes add to synaptic stability
What are the four stages of plasticity?
1. Induction: a postsynaptic neuron "realizes" that a particular input needs to be changed
2. Selectivity: a particular type of change is selected based upon input parameters
3. Expression: The synaptic efficacy is changed
4. Maintenance: this efficacy change is maintained over a long period of time
- The major player in the post synaptic cell is calcium
- - activity causes calcium entry
- signals must be couple/ coordinated
- - presynaptic activity: extracellular activation of glutamate receptors
- - postsynaptics activity: depolarization of the membrane
- the calcium increase occurs only locally
- - most of the effect occurs at the post-synaptic density
- - diffusion and buffering inhibit longer distance effects
- - "pinching" of spine neck inhibits diffusion
- - this means the calcium effects must be local
The post-synaptic density
- during induction there are multiple sources of calcium
- -glutamere is the main initiator of calcium entry
- what happens locally?
- -complex scaffolding network
- -membrane receptors: NMDAR, AMPAR
- -underlying structure: PSD-95 binds NMDAR and other proteins
- -proximity to calcium is important
- Is this signal important?
- -does this input affect my output
- -measured in terms of signal propagation (an AP)
- -remember the depolarization threshold
The selection of input patterns occurs in time and in space
selectivity: spatial dependence
dendritic depolarization decays with distance (unlike action potentials)
Define spike-timing dependent plasticity
synaptic strength is modified based on the timing of the presynaptic action potential in relation to the postsynaptic action potential
Spike Timing Dependent Plasticity, in detail
- directly excite the postsynaptic cell
- -short current pulse
- active the synapse by stimulating the presynaptic neuron
- -before or after the postsynaptic neuron fires
- -one neuron is not enough to cause excitation of the postsynaptic cell (esp not for LTP)
- Explore time-dependence of the presynaptic signal -when does it occur with respect to postsynaptic cell excitation?
- -Does it cause potentiation?
: get the starting point for synaptic strength, perform some experimental manipulation, determine if the synaptic strength has changed, the change between the starting and end points will be due to the experimental manipulation
the excitatory postsynaptic current (EPSC) is a response to a given input where the response is an electrical current
- experimental manipulation: we must define the presynaptic cell firing time, the postsynaptic cell induced action potential, and the time between the two --> these inputs may be manipulated for the experiment
- results: if the synapse hasn't changed, the EPSC won't have changed, change may be measured by delta EPSC, plotting the data shows graph similar to Hebb's postulate
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