Memory in simple organisms- LTP and LTD Flashcards
What are 2 ways of regulating synaptic sensitivity?
- Affecting activity of Ca2+ channel
2. Move channels away from the active zone
What does synaptotagmin do?
Detects when Ca2+ enter the presynaptic bulb-
leads to the release of neurotransmitter
What does plasticity mean?
Synapses become less responsive to stimulation-
due to there being fewer readily available vesicles
Difference between NMDA and AMPA receptors?
NMDA receptors- channel is blocked by Mg2+
Need to depolarise the membrane slightly to remove the Mg2+- then binding will open the channel
What is habituation?
A decrease in responsitivity of sensory neurons when a stimulus is repeated many times
What is sensitisation?
When the nervous system responds to an stimulus with increasing strength
What is the siphon- gill reflex?
When the siphon is touched- the gill withdraws
Where does habituation occur in the aplysia
Habituation occurs due to a decrease in sensitivity at the sensory-motor neuron synapse
What causes sensitisation in the aplysia?
L-29 neurons stimulate sensory neurons with serotonin- leads to longer depolarisations of the sensory neuron- causing more activation of the motor neuron
Why does habituation occur?
Due to the depletion of the synaptic vesicle pool
Why does sensitisation occur?
Due to serotinergic feedback from other sensory neuonrs
What is associative learning?
A learning process in which a new response becomes associated with a particular stimulus
What is non synaptic plasticity?
Changing in synapse strength not directly involving the synapse- modification of the intrinsic excitability of a neuron, unrelated to the amount of n.mitter
What are lymnaea cerebral giant cells involved with?
They permit feeding- not involved in feeding behaviour
What are the main neurons in a simplified hippocampal circuit
CA3
CA1
Dentate gyrus
What is the LTP phenomenon
A high frequency stimulus produces an increased amplitude of the post synaptic response, which is sustained (potentiation) in the CA3 to CA1 synapses
What is co-operativity in LTP?
When two neurons converge and share a synapse- both neurons can be strengthened, even if one pathway is weak
How does LTP occur
Often a postsynaptic event
Critical role for calcium
Calcium activated kinases, which changes the sensitivity of synapses
Summary of early phase of LTP
Calcium activated calmodulin kinase 2
Autophosphorylation of CamK2=
1.Phosphorylates AMPA- increases activity
2.AMPAfication- BIGGER RESPONSES IN POST SYN NEURON
Summary of late phase LTP
cAMP signalling may be critical
Protein synthesis and-
Change in GENE transcription
What is the conclusion in regards to LTP and long term memory?
LTP is necessary for some memory formation
but is NOT sufficient
What is the LTP phenomenon?
Long lasting reduction in synaptic efficacy
What are the 2 types of LTD?
- Depotentiation
2. LTD de novo
What are 4 general mechanisms for LTD induction?
- NMDA receptors
- Low frequency stimulation
- Ca2+ influx- activation of phosphatases
- Glu- can be 5-HT or endocannabinoids
What are the receptors involved in LTD in the cerebellum?
Cav
metabotropic Glu-r
AMPA-r
What occurs when a P.F is stimulated
Glu released
activation of AMPA-r= depol
activation of Glu-r= activation of second messengers
What occurs when a C.F is stimulated?
Depol of P.cell
activation of Cav
intracellular Ca increases
What occurs when both pathways are activated?
Second messengers increase [Ca]i even further
This activates PKC
PKC phosphorylates AMPA receptors- internalising them
=Depressed response from P.cell
What is the Albus-Marr model?
CF input indicated a motor error and weakens the PF-P.cell synapse
How does hippocampal LTD occur?
Low frequency stimulation of CA3-CA1 synapse-
SMALL degree of NMDAr activation
SMALL increase in [Ca]i
More phosphatases than kinases activated
=LTD
Long term memory=?
Distributed, structural change
May be encoded outside the hippocampus
What is the hippocampus important for?
- Formation of new memories (damage- anterograde amnesia)
- Important in spatial memory
- Good at associating different inputs- visual, auditory, smell
What does stressful stimuli cause?
LTD
