Chapter 3: Neuronal Plasticity

Question 1

Briefly explain what the gill withdrawal reflex in Aplysia is and explain the synapse structure that permits it

Answer 1

Normally, the snail uses a siphon to draw water over its gills for oxygen. In the gill withdrawal reflex, the siphon and fills withdraw for protection.

The reflex is due to the GILL SENSORY NEURON and SIPHON NEURON synapsing DIRECTLY into a larger motor neuron that innervates the surrounding gill muscle.

Question 2

In aplysia, sensory neurons typically release ____ onto motor neurons for reflexive behavior

Answer 2

glutamate

Question 3

one mechanism of sensitization may arise from the broadening of __ ___ that the sensory neurons gneerate when something touches a (siphon in aplysia). This phenomenon is called ___ ___ that leads to sensitivity.

How does this trigger sensitivity?

Answer 3

one mechanism of sensitization may arise from the broadening of ACTION POTENTIALS that the sensory neurons gneerate when something touches a (siphon in aplysia). This phenomenon is called PRESYNAPTIC ALTERATION that leads to sensitivity.

What action potentials in sensory neuron broaden, more Ca2+ influxes intot he cell, and increases glutamine release onto the motor neuron because more vesicles are being pushed out of the sensory neuron.

Increased glutamate release from sensory neuron onto motor neuron causes more EPSPs in the motor neuron

Question 4

which neurotransmitter is salient for increasing sensitivty to a controlled stimulus?

Answer 4

serotonin

Question 5

explain the mechanism of how serotonin creates sensitivity in aplysia

Answer 5

1) a stimulus that is not on siphon (ex/ tail shock) activates a serotoniergic neuron
2) excited neuron releases 5HT
3) 5HT binds to GPCR on the sensory neuron
4) GPCR activation leads to cAMP production through the activation of adenylyl cyclase
5) cAMP activates PKA
6) PKA phosphorylates K+ channels in the neuronal membrane and results in LACK of K+ efflux, therefore, the membrane becomes more depolarized.

7) hyperexcitability of neuron because of decreased K+ efflux = more APs = mroe Ca2+ release = more GLUT NT release onto the motor neuron = increased EPSPs of the motor neuron that causes GILL COVERING.

Question 6

GPCRs are _____ receptors (ionotropic/metabotropic

Answer 6

metabotropic; they are not ion channels themselves, but its activation causes the opening of other channels)

Question 7

sensitization has occurred when the general ____ for response has been ___

Answer 7

when the general threshold for response has been lowered.

Question 8

____ stimulation is better than ___ stimulation at creating long lasting sensitivity. Why?

Answer 8

SPACED stimulation is better than MASSED stimulation at creating long lasting sensitivity.

Mass stimulation risks habituation or adaptation or complete death of neuron

Question 9

Long term sensitization requires ____ ___. Where does this occur and why is this necessary?

Answer 9

Requires protein synthesis. Occurs in the cell body and in DENDRITIC RIBOSOMES

necessary because long term sensitization requires STRUCTURAL CHANGE, most likely some sort of growth. If proteins needed to accomplish growth are not already floating in the cell, they must be synthesized.

Question 10

How is CREB activated for protein synthesis during long term sensitization?

Answer 10

CREB gets phosphorylated by PKA when PKA gets activated by cAMP-GPCR 5HT pathway during initial sensitization.

Question 11

If ___ (Transcription factor) is blocked, no protein synthesis will occur and no long term sensitivity is seen.

Answer 11

CREB

Question 12

What does CREB activate?

Answer 12

1) activates ubiquitin hydrolase gene: prevents PKA deacttivation and thus prolongs sensitivity
2) activates proteins for physically growing the neuron.

Question 13

What does ubiquitin hydrolase gene do?

Answer 13

Gets activated by CREB and prevents PKA deactivation and thus prolongs sensitivity

Question 14

Sensitivity for the aplysia snail is ___ synaptic

Answer 14

heterosynaptic.

Question 15

T/F: presynaptic adjustment is the typical method of sensitization in mammals

Answer 15

false. Usually its post synaptic. in snails such as aplysia, they do use presynaptic adjustment as a method of sensitization by facilitating increased glutamate release from sensory neurons.

Question 16

What is tetanic stimulation

Answer 16

high frequency, repetitive stimulation of a neuron that results in a large amount of elevated depolarization because of temporal summation

Question 17

How are synapses strengthened in mammals? (type of stimulation)

Answer 17

by tetanic stimulation.

Question 18

What phenomemon happens to a neuron after tetanic stimulation? (method of sensitivity in mammals)

Answer 18

at first, the neuron gets used to frequency stimulation and the potential goes down during the END of tetanic stimulation.

BUT: the motor neurons response to a single stimulus becomes much larger than it had been before tetanic stimulation. This is called POST TETANIC POTENTIATION.

Question 19

What is post tetanic potentiation? What causes it?

Answer 19

when the motor neurons response to a single stimulus becomes much larger than it had been before tetanic stimulation.

Caused by Ca2+ buildup in the presynaptic terminal due to rapid stimulation before hand.

Question 20

axons that project from the ____ into the ___ gyrus of the hippocampus is known as the ____ pathway.

Answer 20

axons that project from the NEOCORTEX into the DENDATE gyrus of the hippocampus is known as the PERFORANTpathway.

Question 21

what happens if you tetanically stimulate neurons in the perforant pathway?

Answer 21

you will see increased EPSPs in the dendate gyrus in response to a single stimulus afterwards/

Question 22

What is long term potentiaion (in mammals)

Answer 22

an increase in EPSP amplitude that persists for SEVERAL HOURS after the end of tetanic stimulation

Question 23

mammalian hippocampal LTP involves ____ synaptic changes, whereas snail sensitization depends on ___ synaptic modifications

Answer 23

mammalian hippocampal LTP involves POST synaptic changes, whereas snail sensitization depends on PRE synaptic modifications

Question 24

inputs from dif layers of ___ ___ are processed at different levels of the hippocampus

Answer 24

entorhinal cortex

Question 25

which layers of the entorhinal cortices influence the hippocampus the most

Answer 25

layers 2, 3 and 4

Question 26

Hippocampal Circuit between Enterhinal cortex and HC:

EC ___ cells from layer ___ synapse with the HC’s ___ gyrus cells. the ___ gyrus cells of the HC synapse with ___ __ #__, which is packed with ___ neurons.

CA#__ cells then project onto CA#__ region, which contains ____ cells. These cells then relay back to the enterorhinal cortex through the ____ layer.

Answer 26

EC STELLATE cells from layer 2 synapse with the HC’s DENDATE (part of perforant pathway) gyrus cells. the DENDATE gyrus cells of the HC synapse with CORNU AMONUS #3 AREA, which is packed with PYRAMEDAL neurons.

CA#3 cells then project onto CA#1 region, which contains SUB PYRAMEDAL cells. These cells then relay back to the enterorhinal cortex through the 5th layer.

Question 27

Hebb rule

Answer 27

the cellular basis of learning involves strengthening of a synapse that is repeatedly active when the post synaptic neuron fires. Neurons that fire together wire together.

Question 28

What must happen in order for Hebb’s rule to apply?

Answer 28

synapses will only be strengthened only if they are active when the POST SYN NEURON was depolarized enough to ACTUALLY FIRE.

Question 29

How is hebb’s principle affiliated with classical conditioning circuit?

Answer 29

concurrent stimulation of a neuron that is ALREADY SYNAPSED (somatosensory neuron) along with a neuron that is NOT already synapsed (ex/ auditoy) allows the synaptic formation of cells that were not originally paired together.

repeated stimulation of an auditory neuron (sound) with a somatosensory neuron (air puff) can cause the motor neuron to fire when an auditory neuron fires by itself (blink when you hear a specific tone)

Question 30

Induction vs stabilization of LTP

Answer 30

induction of LTP = triggering long term potentiation

stabilization of LTP = maintaining synapses that were newly formed.

Question 31

Explain the role of NMDA receptor on LTP INDUCTION

Answer 31

Recall: NMDA is voltage gated and ligand gated. The membrane must be intially already depolarized in order for NMDA to open in response to glutamate (MG2+ needs to dislodge).

In order to depolarize the cell enough for NMDA receptors to open, there are also AMPA receptors that open in response to glutamate and let Na+ into the cell. Na+ induces depolarization and displaces MG2+ from NMDA receptor

NMDA opening lets Ca2+ into the cell.

Ca2+ binds to calmodulin

Ca2+-calmodulin complex activates CAMKII kinase, which facilitates the insertion of additional AMPA receptors

more AMPA receptors= cell is more responsive to glutmate and causes more EPSPs.

Question 32

What is CaMKII Kinase?

Answer 32

an enzyme that gets activated by Ca2+=calmodium complex (triggered by NMDA receptor opening) that inserts more AMPA receptors onto the membrane of a cell, causing the cell to be MORE SENSITIVE to glutamate than it already is.

Question 33

CaMKII kinase activity by inserting AMPA receptors on cell membrane in response to synaptic stimulation is an example of ___ ___ modification

Answer 33

post synaptic modification. Method of mammalian long term potentiation.

Question 34

Why does the role of NMDA receptor (which causes an increase in glutmate sensitivity in the cell because more AMPA receptors get implanted in the membrane) facilitate LTP?

Answer 34

the increased glutamate sensitivity FACILITATES DENDRITIC SPINE GROWTH in PYRAMEDAL CELLS.

Question 35

What would happen to dendrites if you bath the HC in drugs that block NMDA receptors before undergoing tetanic stimulation?

Answer 35

it would prevent dendritic spine growth and thus no LTP would occur even after tetanic stimulation.

Question 36

How do dendritic spikes contribute to LTP?

Answer 36

1) AP reaches terminal button of a strong synapse and depolarizes a pyramedal cell
2) the post synaptic pyramedal cell triggers an AP at its own axon hillock in response to stimulation
3) dendritic spike washed back along the dendrite and PRIMES (depolarizes membrane) NMDA RECEPTORS in dendritic SPINES
4) dendritic spike may initiate glutamate release onto a WEAKLY SYNAPSED adjacent neuron.
5) glutamate release onto adjacent (post dendritic spine syn) neuron interacts with its AMPA receptors, depolarizing the weakly synapsed cell
6) depolarization of weakly synapsed cell can open NMDA receptors on the post syn membrane, causing Ca2+ influx and CAMKII activation, increasing the number of AMPA receptors on the membrane
7) LONG TERM POTENTIATION at the dendritic spine and post syn neuron has occurred: the synapse is strengthened.

Question 37

In terms of Hebb’s Rule, the increase in connection strength can be brought on by 2 things:

Answer 37

1) more transmitter release per action potential (ex/ because (ex/ 5HT causes more cAMP causes more PKA causes decreased K+ efflux causes depolarization causes increased #APs causes more transmitter release)
2) post synaptic changes (more AMPA glutamate receptors causes post syn neurons to become more sensitive to glutamate and therefore more EPSPs are elicited)

Question 38

When studying glutamate induced dendritic spine growth, why must the tissue be bathed in Mg2+ free solution?

Answer 38

removing Mg2+ = NMDA receptors can open at lower membrane potentials, and thus allows Ca2+ influx. Prevents researchers from needing to depolarize the cell before running the experiment.

Question 39

Which part of LTP (induction or stabilization) is protein synthesis involved in ?

Answer 39

protein synthesis is needed for STABILIZATION, whereas NMDA receptors and glutamate and dendritic spine growth and dendritic spike-induced synapse formation in involved in LTP induction

Question 40

Synaptic tagging hypothesis

Answer 40

the ideas the proteins get syntheized in cell body and get packaged and taken to dendrites

Question 41

How do we know that dendritic ribosomes are also necessary for LTP stabilization and not just cell body ribosomes?

Answer 41

because if you bathe dendrites in protein synthesis inhibitor, only transient synaptic potentiation is possible. (post tetanic potentiation)

Question 42

two proteins that are synthesized that help with LTP stabilization

Answer 42

1) ARC

2) CaMKII; adds AMPA receptors onto membrane

Question 43

___ changes such as histone deacetylation can make memories more persistent.

Answer 43

EPIGENETIC CHANGES. Blocking protein synthesis permits transient potentiation but prevents LTP stabilization.

Question 44

___ ___ peptide acts as a destabilizer and causes potentiated synapses to return back to baseline

Answer 44

ZETA INHIBITORY PEPTIDE.

Question 45

What is long term depression?

Answer 45

the weakening of synapses seen after bouts of particular presynaptic stimulation

Question 46

2 primary fibers associated in the cerebellum

Answer 46

1) purkinje cells

2) granular cells aka parallel fibers

Question 47

What kind of fibers are associated with cerebellar purkinje cells? What do they do?

Answer 47

Climbing fibers wrap around purkinje fibers. The climbing fibers release glutamate and DEPOLARIZE the purkinje cell.

Question 48

Mechanism of long term depression in cerebellum

Answer 48

activating climbing fibers and parallel fibers simultaneously causes the PARLLEL fiber input onto a Purkinje fiber to decrease in strength even further.

EPSP in climbing fiber causes Ca2+ influx through VG Ca2+ channels and NMDA receptors at the climbing fiber synapses. Parallel fibers can release Ca2+ from their organelles through an IP3-coupled metabotropic glutamate receptor.

activation of Climbing and parallel fibers causes huge spikes in Ca2+ and can trigger PKC release in the PARALLEL GIBER, causing the REMOVAL of AMPA receptors from the post syn side of synapse and WEAKENS SYNAPSE between PARALLEL AND PURKINJE FIBERS.

Question 49

Long term depression allows you to _____ something. LTD is also anti Hebbian. What does this mean?

Answer 49

LTD allows you to UNLEARN SOMEtHING

Anti hebbian: cells that fire together become less wired together.

Question 50

What is Spike timing dependent plasticity?

Answer 50

cells exhibit LTP or LTD depending on how they fire

If POST SYN cell fires AFTER PRE SYN activity, then LTP occurs

If POST syn cell fires BEFORE PRE SYN activity (maybe from a dif source)?, the LTD occurs and WEAKENS the synapse between the pre and post syn cell.

Question 51

Hebbs law states that neurons must be ___ in order to be strengthened synaptically

Answer 51

must be active.

Question 52

synaptic scaling. How does this occur? Why is this beneficial?

Answer 52

neurons increase the average strength of their synaptic inputs after they have been relatively inactive, and then they decrease the strength of those inuts when neurons have been active.

most likely due to addition and removal of AMPA receptors

scaling ensures neurons are not dormat for long and prevents excitotoxic damage in neurons that are too active. (be decreasing the strength of synapses when they are firing a lot)

Synaptic scaling is involved in mitigating epilepsy

Question 53

___ of dendritic spine turnover is linked to learning

Answer 53

RATE of adult dendritic spine turnover

Question 54

CAPACITY for learning is proportional to the degree of ___

the ACT of learning is proportional to the degree of ____ of dendritic spine and axon collateral formation.

Answer 54

CAPACITY for learning is proportional to the degree of PLASTICITY (FORMATION of dendritic spines)

the ACT of learning is proportional to the degree of STABILIZATION of dendritic spine and axon collateral formation.

Question 55

as animals learn important SENSORY info, cortical territory representing that info ____ in a brain map

Answer 55

EXPANDS.

unsed info takes up less space on the tonotopic ma

Question 56

learning related changes in the auditory map requires ____ release in the neocortex

Answer 56

Ach

Question 57

Motor cortex plasticity:

as animals learn a new motor skill, portions of the motor map related to that skill tend to expand at the expense of other ares.

the more ____ the task, the GREATER the expansion, but ___ ___ of an unskilled task causes little or no plasticity.

Give an example of motor cortex plasticity.

Answer 57

the more DIFFICULT the task, the GREATER the expansion, but REPETITIVE PERFORMANCE of an unskilled task causes little or no plasticity.

An example can be seen about rats who learn a food task. Rats who learn a food handling task have greater neuronal motor area dedicated to dexterity of their paws and wrists, but shrunken areas of space dedicated to elbows and shoulder movement that aren’t as important for the food task.

Question 58

condition reaction tasks causes an increased number of axonal varicosities in the:

Answer 58

cerebellar nuclei.

Question 59

How does environment impact brain size? Why?

Answer 59

animals living in an enriched environment tend to have a larger neocortex than deprived animals.

Due to the growth of individual neurons and glial cells. The enriched environment rats have a larger number of synapses.

Question 60

___ or function experiments answer the question: is the proposed mechanism NECESSARY for a specific form of learning or memory?

Answer 60

loss of function

Question 61

___ of function experiments answers the question: is the proposed mechanism SUFFICIENT for a form of learning or memory?

Answer 61

gain of function.

Question 62

establishing a causal link between neural phenomena is best done by combining ___ of function and ___ of function experiments with ____ data.

Answer 62

establishing a causal link between neural phenomena is best done by combining GAIN of function and LOSS of function experiments with CORRELATIVE data.