Memory in simple organisms- LTP and LTD

Question 1

What are 2 ways of regulating synaptic sensitivity?

Answer 1

1. Affecting activity of Ca2+ channel

2. Move channels away from the active zone

Question 2

What does synaptotagmin do?

Answer 2

Detects when Ca2+ enter the presynaptic bulb-

leads to the release of neurotransmitter

Question 3

What does plasticity mean?

Answer 3

Synapses become less responsive to stimulation-

due to there being fewer readily available vesicles

Question 4

Difference between NMDA and AMPA receptors?

Answer 4

NMDA receptors- channel is blocked by Mg2+

Need to depolarise the membrane slightly to remove the Mg2+- then binding will open the channel

Question 5

What is habituation?

Answer 5

A decrease in responsitivity of sensory neurons when a stimulus is repeated many times

Question 6

What is sensitisation?

Answer 6

When the nervous system responds to an stimulus with increasing strength

Question 7

What is the siphon- gill reflex?

Answer 7

When the siphon is touched- the gill withdraws

Question 8

Where does habituation occur in the aplysia

Answer 8

Habituation occurs due to a decrease in sensitivity at the sensory-motor neuron synapse

Question 9

What causes sensitisation in the aplysia?

Answer 9

L-29 neurons stimulate sensory neurons with serotonin- leads to longer depolarisations of the sensory neuron- causing more activation of the motor neuron

Question 10

Why does habituation occur?

Answer 10

Due to the depletion of the synaptic vesicle pool

Question 11

Why does sensitisation occur?

Answer 11

Due to serotinergic feedback from other sensory neuonrs

Question 12

What is associative learning?

Answer 12

A learning process in which a new response becomes associated with a particular stimulus

Question 13

What is non synaptic plasticity?

Answer 13

Changing in synapse strength not directly involving the synapse- modification of the intrinsic excitability of a neuron, unrelated to the amount of n.mitter

Question 14

What are lymnaea cerebral giant cells involved with?

Answer 14

They permit feeding- not involved in feeding behaviour

Question 15

What are the main neurons in a simplified hippocampal circuit

Answer 15

CA3
CA1
Dentate gyrus

Question 16

What is the LTP phenomenon

Answer 16

A high frequency stimulus produces an increased amplitude of the post synaptic response, which is sustained (potentiation) in the CA3 to CA1 synapses

Question 17

What is co-operativity in LTP?

Answer 17

When two neurons converge and share a synapse- both neurons can be strengthened, even if one pathway is weak

Question 18

How does LTP occur

Answer 18

Often a postsynaptic event
Critical role for calcium
Calcium activated kinases, which changes the sensitivity of synapses

Question 19

Summary of early phase of LTP

Answer 19

Calcium activated calmodulin kinase 2
Autophosphorylation of CamK2=
1.Phosphorylates AMPA- increases activity
2.AMPAfication- BIGGER RESPONSES IN POST SYN NEURON

Question 20

Summary of late phase LTP

Answer 20

cAMP signalling may be critical
Protein synthesis and-
Change in GENE transcription

Question 21

What is the conclusion in regards to LTP and long term memory?

Answer 21

LTP is necessary for some memory formation

but is NOT sufficient

Question 22

What is the LTP phenomenon?

Answer 22

Long lasting reduction in synaptic efficacy

Question 23

What are the 2 types of LTD?

Answer 23

1. Depotentiation

2. LTD de novo

Question 24

What are 4 general mechanisms for LTD induction?

Answer 24

1. NMDA receptors
2. Low frequency stimulation
3. Ca2+ influx- activation of phosphatases
4. Glu- can be 5-HT or endocannabinoids

Question 25

What are the receptors involved in LTD in the cerebellum?

Answer 25

Cav
metabotropic Glu-r
AMPA-r

Question 26

What occurs when a P.F is stimulated

Answer 26

Glu released
activation of AMPA-r= depol
activation of Glu-r= activation of second messengers

Question 27

What occurs when a C.F is stimulated?

Answer 27

Depol of P.cell
activation of Cav
intracellular Ca increases

Question 28

What occurs when both pathways are activated?

Answer 28

Second messengers increase [Ca]i even further
This activates PKC
PKC phosphorylates AMPA receptors- internalising them
=Depressed response from P.cell

Question 29

What is the Albus-Marr model?

Answer 29

CF input indicated a motor error and weakens the PF-P.cell synapse

Question 30

How does hippocampal LTD occur?

Answer 30

Low frequency stimulation of CA3-CA1 synapse-
SMALL degree of NMDAr activation
SMALL increase in [Ca]i
More phosphatases than kinases activated
=LTD

Question 31

Long term memory=?

Answer 31

Distributed, structural change

May be encoded outside the hippocampus

Question 32

What is the hippocampus important for?

Answer 32

1. Formation of new memories (damage- anterograde amnesia)
2. Important in spatial memory
3. Good at associating different inputs- visual, auditory, smell

Question 33

What does stressful stimuli cause?

Answer 33

LTD