Chp 2 - Mechanisms of Synaptic Plasticity Flashcards
Hebb’s Cell Assembly
modified ensembles of neurons that are called cell assemblies that are repeatedly stimulated during a certain process and as a result the synaptic connections strengthen
neurobiologists are motivated by the belief that the information content of our various experiences persist in a retrievable form because…
the synapses can be modified by experiences
what is the general phenomenon of plasticity
that plasticity is a mechanism of memory (not memory itself) and is a mechanism which we acquire and store memory, provides the capacity for memory.
what is the critical site for plasticity/ plastic change
synapse
Hebb’s learning rule
cells that fire together wire together, more likely to reactivate
when cells persistently activate nearby cells, they grow stronger
when are connections between neurons changed in memory
when the synapse that links them are modified
___ is important for episodic memory
hippocampus
What structure was most important in the hippocampus and why
trisynaptic circuit because its organization allowed for studying of neurons from one subfield for another
How did Bliss and Lomo discover LTP
stimulated perforant path and recording in the dentate gyrus. weak stimulus was applied to perforant path and measured synaptic activity. strong stimulus to perforant path and evoked more synaptic activity than weak. strong stimulus produced enduring increase in synaptic response than weak and enhanced response called LTP
What does LTP allow the studying of
important discovery because provided a way to study how synaptic strength can be modified by experience
is a model system to study mechanisms of learning and memory
Explain in vitro preparation
dissecting thin slice of tissue from hippocampus, place in special chamber with chemical that keep tissue function for hours, stimulating electrode then positioned to deliver electrical current to specific set of fibers and recording electrode is inserted into the extracellular space in pyramidal cells, it records excitatory postsynaptic potential (EPSP) (how long action potential fires) in particular area known as the field potential. field potential is what is measured in LTP (field potential is the sum electrical activity)
What are the four functions a neuron serves
- input device (receives messages from others)
- integrative device (combines messages received)
- conductive output device (sends information to muscles, neurons, organs)
- representation device (stores information about past experiences and synaptic strength
synapse composed of
presynaptic terminal and postsynaptic component
what happens after action potential arrives in the presynaptic axon terminal
nt molecules are released from synaptic vesicles into synaptic cleft that bind to specific receptors that create chemical or electrical signal in postsynaptic cell. this excitatory or inhibitory postsynaptic potential changes the excitability of the postsynaptic cell
what changes the postsynaptic potential of a neuron
different concentrations, sizes of ion channels, permeability of membranes, pumps, etc.
depolarization vs. hyperpolarization
depolarization = drives neuron to generating action potential and membrane potential becomes less negative (closer to zero)
hyperpolarization = membrane potential becomes more negative, drives neuron away from generating action potential
define field EPSP
measure of the strength of a group of synapses, reflects the depolarization of many synapses. the strength of a synapse is defined by the change in transmembrane potential from the activation of postsynaptic nt receptors
ways to record postsynaptic potentials
intracellular electrode = penetrates neuron and detects positive ions flowing into the neuron indicating depolarization
extracellular electrode = placed in extracellular fluid and measures electrical potentials between fluid and ground electrode
what does the slope of fEPSP indirectly measure
strength of the synaptic connections in the electrode because it measures the positive ions entering the postsynaptic neuron (flowing away from extracellular recording electrode, making it more positive inside and depolarizing)
increase in fEPSP means
increase in synaptic strength (measured by how much postsynaptic depolarization is produced)
recording electrode to measure LTP detects what 3 electrical currents
- stimulus artifact
- fiber volley (the action potential generated by electrical stimulus)
- the fEPSP detected as the downward slope of the waveform
how to calculate % of baseline and what it represents
T2/T1 x 100 = % baseline
represents difference of fEPSP prior to inducing stimulus (t1) and when inducing stimulus is present (t2)
long term depression
when synaptic activity weakens the strength of synaptic connection when a low frequency stimulus is delivered for about 15 minutes
why LTP and LTD phenomenon so interesting to learning and memory research
- cooperativity = LTP requires cooperative interaction of afferent fibers
- specificity = LTP restricted to synapses activated rather than all synapses that contact same neuron
- associativity = synapse which cannot produce LTP with weak input can undergo LTP when synapse is coactivated via a strong input
signaling cascade
initiated by first messenger (such as nt or hormone) binds to cell surface receptor and initiates intracellular activity -> second messengers are molecules that relay signals from receptors on the cell surface to target intracellular protein kinases and phosphatases that target other proteins
1st mess-2nd mes-protein-both kinases and phosphatases-structural and function proteins
why are second messengers so rapid
their production does not depend on slow translation and transcription processes
this rapid production allows for amplification of 1st messenger cells inside the cell
kinases
proteins that change function of other proteins
composed of inhibitory and catalytic unit
in active state from binding of secondary messenger, unit is dissociated and kinase is active which phosphorylates other proteins and changes their function
phosphatases
proteins that remove phosphate groups
what are four steps of strengthening synapses
- generation 2. stabilization 3. consolidation 4. maintenance
