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Flashcards in section 11.8 Deck (17)
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1
Q

Hebb’s hypothesis

A

enduring facilitations of synaptic transmission are the neural bases of learning and memory.

2
Q

Bliss and Lømø

A

showed that there is a facilitation of synaptic transmission following high-frequency electrical stimulation applied to presynaptic neurons. Termed long-term potentiation (LTP).

3
Q

LTP has two key properties that Hebb proposed as characteristics of the physiological mechanisms of learning and memory:

A
  • LTP can last for a long time – for several months after multiple stimulations.
  • LTP develops only if the firing of the presynaptic neuron is followed by the firing of the postsynaptic neuron; it does not develop when either neuron fires and the other does not.
4
Q

The co-occurrence of firing in presynaptic and postsynaptic cells is now recognized as

A

the critical factor in LTP.

5
Q

Hebb’s postulate for learning

A

assumption that co-occurrence is a physiological necessity for learning and memory.

6
Q

Additional support for the idea that LTP is related to the neural mechanisms of learning and memory has come from several observations:

A
  • LTP can be elicited by low levels of stimulation that mimic normal neural activity.
  • LTP effects are most prominent in structures that have been implicated in learning and memory, such as the hippocampus.
  • Behavioral conditioning can produce LTP-like changes in the hippocampus.
  • Any drugs that influence learning and memory have parallel effects on LTP.
  • The induction of maximal LTP blocks the learning of a Morris water maze until the LTP has subsided.
  • Mutant mice that display little hippocampal LTP have difficulty learning the Morris water maze.
  • LTP occurs at specific synapses that have been shown to participate in learning and memory in simple invertebrate nervous systems.
7
Q

LTP is a three part process:

A

induction, maintenance, and expression – that is, the processes by which high-frequency stimulations induce LTP (learning), the changes responsible for storing LTP (memory), and the changes that allow it to be expressed during the test (recall).

8
Q

NMDA receptor

A

prominent at the synapses at which LTP is commonly studied; a receptor for glutamate.

9
Q

An NMDA receptor does not respond maximally unless two events occur simultaneously:

A

glutamate must bind to it, and the postsynaptic neuron must already be partially depolarized.

10
Q

This dual requirement stems from the fact that the calcium channels associated with NMDA receptors allow only

A

small numbers of calcium to enter the neuron unless the neuron is already depolarized when glutamate binds to the receptors; it is the influx of calcium ions that triggers action potentials and the cascade of events in the postsynaptic neuron that induces LTP.

11
Q

The requirement for the postsynaptic neurons to be partially depolarized when the glutamate binds to them is an

A

extremely important characteristic of conventional LTP because it permits neural networks to learn associations.

12
Q

The requirement for co-occurrence and the dependence of NMDA receptors on simultaneous binding and partial depolarization mean that

A

under natural conditions, synaptic facilitation records the fact that there has been simultaneous activity in at least two converging inputs to the postsynaptic neuron.

13
Q

Dendritic spines

A

the calcium ions that enter a dendritic spine do not readily pass out of it, and thus they exert their effect locally.

14
Q

LTP causes structural changes and many changes have been described including

A

increases in number and size of synapses, increases in number and size of postsynaptic spines, changes in presynaptic and postsynaptic membranes, and changes in dendritic branching.

15
Q

transcription factors

A

intracellular proteins that bind to DNA and influence the operation of particular genes; activated by neural activity.

16
Q

At synapses where NMDA receptors are predominant

A

the signal that passes from the postsynaptic neurons back to the presynaptic neurons takes the form of the soluble-gas neurotransmitter nitric oxide. Nitric oxide is synthesized in the postsynaptic neurons in response to calcium influx and then diffuses back into the terminal buttons of the presynaptic neurons.

17
Q

long term depression (LTD)

A

occurs in response to prolonged low-frequency stimulation of presynaptic neurons.