Chp 2 - Mechanisms of Synaptic Plasticity

Question 1

Hebb’s Cell Assembly

Answer 1

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

Question 2

neurobiologists are motivated by the belief that the information content of our various experiences persist in a retrievable form because…

Answer 2

the synapses can be modified by experiences

Question 3

what is the general phenomenon of plasticity

Answer 3

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.

Question 4

what is the critical site for plasticity/ plastic change

Answer 4

synapse

Question 5

Hebb’s learning rule

Answer 5

cells that fire together wire together, more likely to reactivate
when cells persistently activate nearby cells, they grow stronger

Question 6

when are connections between neurons changed in memory

Answer 6

when the synapse that links them are modified

Question 7

___ is important for episodic memory

Answer 7

hippocampus

Question 8

What structure was most important in the hippocampus and why

Answer 8

trisynaptic circuit because its organization allowed for studying of neurons from one subfield for another

Question 9

How did Bliss and Lomo discover LTP

Answer 9

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

Question 10

What does LTP allow the studying of

Answer 10

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

Question 11

Explain in vitro preparation

Answer 11

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)

Question 12

What are the four functions a neuron serves

Answer 12

1. input device (receives messages from others)
2. integrative device (combines messages received)
3. conductive output device (sends information to muscles, neurons, organs)
4. representation device (stores information about past experiences and synaptic strength

Question 13

synapse composed of

Answer 13

presynaptic terminal and postsynaptic component

Question 14

what happens after action potential arrives in the presynaptic axon terminal

Answer 14

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

Question 15

what changes the postsynaptic potential of a neuron

Answer 15

different concentrations, sizes of ion channels, permeability of membranes, pumps, etc.

Question 16

depolarization vs. hyperpolarization

Answer 16

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

Question 17

define field EPSP

Answer 17

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

Question 18

ways to record postsynaptic potentials

Answer 18

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

Question 19

what does the slope of fEPSP indirectly measure

Answer 19

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)

Question 20

increase in fEPSP means

Answer 20

increase in synaptic strength (measured by how much postsynaptic depolarization is produced)

Question 21

recording electrode to measure LTP detects what 3 electrical currents

Answer 21

1. stimulus artifact
2. fiber volley (the action potential generated by electrical stimulus)
3. the fEPSP detected as the downward slope of the waveform

Question 22

how to calculate % of baseline and what it represents

Answer 22

T2/T1 x 100 = % baseline
represents difference of fEPSP prior to inducing stimulus (t1) and when inducing stimulus is present (t2)

Question 23

long term depression

Answer 23

when synaptic activity weakens the strength of synaptic connection when a low frequency stimulus is delivered for about 15 minutes

Question 24

why LTP and LTD phenomenon so interesting to learning and memory research

Answer 24

1. cooperativity = LTP requires cooperative interaction of afferent fibers
2. specificity = LTP restricted to synapses activated rather than all synapses that contact same neuron
3. associativity = synapse which cannot produce LTP with weak input can undergo LTP when synapse is coactivated via a strong input

Question 25

signaling cascade

Answer 25

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

Question 26

why are second messengers so rapid

Answer 26

their production does not depend on slow translation and transcription processes
this rapid production allows for amplification of 1st messenger cells inside the cell

Question 27

kinases

Answer 27

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

Question 28

phosphatases

Answer 28

proteins that remove phosphate groups

Question 29

what are four steps of strengthening synapses

Answer 29

1. generation 2. stabilization 3. consolidation 4. maintenance