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BIO 435

Synaptic Plasticity

Define plasticity 1. changes in the structure and function of the nervous system due to experience 2. can strengthen or weaken synapses 3. can be short-term or long-term
What are ways that structure and function of nervous system can change (plasticity) 1. number of receptors 2. number of synapses 3. amount of NTs released 4. number of neurons
Describe synaptic facilitation - a short-term type of plasticity -the 2nd postsynaptic potential is larger than the first -only lasts for milliseconds -occurs when Ca2+ builds up in the presynaptic neuron builds up
Explain why the 2nd postsynaptic potential is greater in synaptic facilitation If the second AP occurs soon enough after the first, there is still enough Ca2+ left. Therefore, there is a greater amount of calcium ions in the presynaptic neuron due to the creation of more for the second potential. Therefore, with greater Ca2+, there is more glutamate released and there is a larger EPSP
Describe synaptic depression -a type of short-term plasticity -sustained activity causes NTs release to decrease -results from a depletion of pool of reserve vesicles (therefore there is no way to release NTs)
What did Eric Kandel's research with Aplysia study? Habituation and sensitization; when more water was squirted on the siphon or it was touched, the gills would withdraw
Define habituation The magnitude of withdrawal decreases over time (when siphon is continuously touched, the gill is withdrawn less and less
Why does habituation occur? Each time the motor neuron is activated, the resulting EPSP becomes smaller (most likely due to synaptic depression and depletion of vesicles in sensory neuron)
What would occur if you unexpectedly shocked the head or tail of the aplysia? The withdrawal response for the withdrawal reflex would be greater. This new sensitization would then last for about a hour
What is the name of the synapse involved in early sensitization? the axo-axonal synapse (includes serotonin modulatory neuron and sensory neuron synapsing on the motor neuron)
Describe the sensitization pathway 1.The sensitizing stimulus is received 2.Serotonin from a serotonin modulatory neuron that is part of axo-axonal synapse releases serotonin 3.Serotonin release decreases probability of K+ channels opening the axon terminal during the action potential 4. Less K+ channels opening means a greater depolarization 5. More Ca2+ channels are able to open resulting in greater NTs release 6. More vesicles dock at the membrane
What affects the duration of sensitization? The number of shocks received
What is the PKA? protein kinase A (cAMP dependent protein kinase)
What does repeated activation of PKA result in? Long-term sensitization due to transcription of synaptic growth proteins
What happens when the presynaptic and postsynaptic neuron activate simultaneously? The synapse between the two is strengthened and neurons (neurons that fire together wire together)
What happens when presynaptic neurons is active when postsynaptic neuron is not (or is only weakly active)? The synapse between the two is weakened (neurons that fire out of sync lose their link)
In what part of the brain is long-term potentiation most extensively studied? hippocampus
What does the high frequency stimulation (tetanus) of CA3 neurons result in? An increase in the response from CA1 neurons
How long can tetanus of CA3 and CA1 neurons last? days, weeks, months, or even a lifetime (this is a long-term potentiation that can occur naturally)
Does it matter where the synapse is placed for potentiation to occur? Yes, potentiation is site specific (the closer synapse is to the terminals, the stronger it is)
Describe the process of early LTP 1. Tetanus depolarizes presynaptic neurons enough to open NMDA (glutamate) receptors 2. Ca2+ activates protein kinases (PKC, CAMKII 3. The released protein kinases phosphorylate AMPA receptors and add more AMPA receptors to the postsynaptic cell (receptor trafficking occurs during this period of potentiation)
Describe the process of late LTP 1. If enough Ca2+ enters, CREB (cAMP-response element binding protein that regulates the expression of genes is produced and gene transcription is modulated 2. This often results in the growth of new synapses
What does late LTP require? Protein synthesis
What causes long-term depression (LTD)? low frequency stimulation (levels of Ca2+ decrease and activates phosphatases; AMPA receptors then dephosphorylated and removed from the synapse)
When does long-term depression occur in the cerebellum? (not a life stage) Cerebellum is in charge of movement feedback and if movement went as planned. If movement of was faulty, LTD occurs so body doesn't make wrong movement again
What type of cells receive input in the cerebellum? Purkinje neurons
How are purkinje neurons involved in LTD? 1. Purkinje cells receive many synapses from each climbing fiber. These climbing fibers are activated when there is an error signal. 2. Purkinje cells receive one synapse from tons of parallel fibers (which release glutamate). Parallel fibers activated when plan is initiated
What occurs when climbing fibers and parallel fibers are active simultaneously? Subsequent EPSPs are induced by parallel fibers only (The error signal from the climbing fiber only affects the one parallel fibers
Why is there a decrease in EPSPs in purkinje cells when error signal is induced by the climbing fibers? Because purkinje cells have decreases cell response to glutamate
Describe the cellular process of LTD 1. Climbing fibers cause massive depolarization 2. Depolarization causes opening of the voltage-gated Ca2+ channels 3. Parallel fibers release glutamate and activates AMPA receptors and mGluRs 4. Massive influx of Ca2+ causes reduction in AMPA receptors on purkinje cell dendrites (only on the part of the dendrite in contract with active parallel fiber)
What causes the internalization (removal of receptors from membrane) of AMPA receptors? Activation of PKC by Ca2+
During what time during life does the total number of synapses and synapses per mm3 increase? 3rd trimester and first year of childhood
What happens to synapses as you age? The synapses are pruned and the brain gets ride of synapses you don't use
What is the formation of ocular dominance columns in layer 4 dependent on? The early postnatal experience
Define arborization The fine branching structure at the end of a nerve fiber
What happens to LGN axons in V1 as a result of deprivation? Arborization
Why does capacity for change decrease as we age? 1. decreases ability for axon growth 2. changes in receptor composition and function 3. changes in other pathways that constrain plasticity
What is neurogenesis? the formation of new neurons
Where does neurogenesis occur? hippocampus and olfactory bulb (but don't know purpose of these new neurons in the olfactory bulb)
Why is neurogenesis in the hippocampus important? New neurons are essential for SSRIs (antidepressants) to function; exercise also impacts new neuron generation
Created by: keiannaowens
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