Week Four - Synaptic & Brain Plasticity Flashcards
What is Plasticity?
The capacity of the nervous system to change in response to environmental stimuli.
It is an adaptive response and present at multiple levels
What 3 levels is plasticity present at?
Genetic/Molecular
Neurophysiological
Functional
What is plasticity key for?
Learning and memory
Our ability to learn depends on what?
The plasticity of the circuits in the brain (the ability of neurons to make lasting changes in the efficiency of their synaptic transmission
Hebb’s Law is often paraphrased as
Neurons that fire together wire together
What are the 3 pathways in the Hippocampus
Perforant Path
Mossy Fibre Pathway
Schaffer’s Collaterals Pathway
High frequency stimulation can result in what?
Can produce a long lasting increase in synaptic strength known as long-term potentiation
Low rate stimulus can produce what?
A long lasting decrease in synaptic strength known as long-term depression
What is long-term potentiation?
A process by which synaptic connections between neurons become stronger with frequent activation
Where does Non-Associative LTP occur?
In the schaffer fibres from CA3 to CA1 and in the mossy fibres from the dentate gyrus to CA3
Key concept of NALTP?
Facilitation is presynaptic and does not require NMDA stimulation
Where does Associative LTP occur?
Occurs in the CA3 and CA1 pathways
Key concept of ALTP?
Required NMDA stimulation and CA2+ entry into the postsynaptic neuron
Describe a non-associative LTP
Two stimulating electrodes each activate separate schaffer collateral fibres, providing a test and control synaptic pathways
In a non-associative LTP what does the magnitude of change vary upon?
How many trains of stimulation are applied
What is the molecular basis of associative LTP?
NMDA receptor behaves like a molecular “and” gate: The channel opens (to induce LTP) only when glutamate is bound to NMDA receptors and the postsynaptic cell is depolarized to eliminate the Mg2+ block of the NMDA channel. Thus, the NMDA receptor can detect the coincidence of two events.
The Ca2+ ions that enter the cell through the channel activate postsynaptic protein kinases. These kinases may act postsynaptically to insert new AMPA receptors into the postsynaptic spine, thereby increasing the sensitivity to glutamate.
What are the most widely used organisms for the study of cellular foundations?
mice, Drosophila, the sea slug Aplysia, and honeybees. Also birds, especially because of their ability for song learning.
Why do we study the Aplysia?
Aplysia does not really show a great variation of behaviour. However, it can learn and it has only 20,000 neurons, approx. 2,000 in each of its ten ganglia. Most importantly these neurons have large stomata.
What causes the gill withdrawal reflex?
Stimulation of the siphon.
What occurs after repeated stimulation of the sensory neuron?
Less neurotransmitters are released by the sensory neuron (habituation)
What is the process of Sensitisation?
A harmful stimulus is applied to the tail or the head before applying the innocuous stimulus.
Why is the process of sensitization, heterosynaptic?
Because it involves presynaptic facilitation mediated by a facilitating neuron that stimulates
(1) the siphon sensory neuron at the level of the soma
(2) potentiates the release of neurotransmitter from the siphon sensory neuron terminal.
What is imprinting?
Process whereby early sensory experience modifies behaviour
What are critical periods?
temporal windows of opportunity. If it is essential for an experience to occur within a particular interval, it is called a critical period
What is a sensitive period?
When the effect of an experience has a great effect on development during that period but development is not exclusive to that period and can occur outside the interval
What is different in musicians brain than others?
the size of the omega sign (larger)
What did Paul Broca discover?
That adult patients with lesions in the left frontal lobe displayed aphasia
What occurs when there is no visual input to the cortex?
An expansion of auditory and somatosensory cortices
What are the 2 components of intermodal reorganisation at the cortical level?
(1) The recruitment of former visual centres by somatosensory and auditory inputs is one of them.
(2) Expansion of cortical territories dedicated to process somatosensory and auditory information.
What do these shifts reflect?
the relocation and transfer of somatosensory and auditory functions to the former visual cortex.
How is plasticity made possible in the adult brain?
By the alteration of their synaptic strength, by the formation of new connections and by adding new neurons
Where does adult neurogenesis occur?
in the dentate gyrus of the hippocampus
How does ecstasy alter adult neurogensis?
Exposure to it decreases the survival of neuronal precursors in the DG
How does alcohol alter adult neurogenesis?
Alcohol potentiates the neurotoxic effects of MDMA on neurogenesis and produces long-term memory deficits
What is something that occurs when we reduce the hippocampal neurogenesis after irradiation?
reduction increases cocaine intake and the rewarding value of cocaine, and retards extinction of cocaine seeking
How does Depression affect the hippocampus?
Depressed patients show decreased hippocampal volume (20%)
Depression is associated with?
A severe atrophy of the CNS
What does antidepressant medication do?
Enhances neural plasticity and hippocampal neurogenesis
What occurs in ageing regarding neurogenesis?
There is decreased plasticity and there is psychiatric vulnerability
What is an important promoter of hippocampal neurogensis?
Aerobic exercise
What occurs when we are in enriched environments?
We have an increased number of synapses and larger dendritic arbours
It can also lead to the formation of neurons and reverses the loss of neurons on the hippocampus and memory impairment following chronic stress
