Week 3 Flashcards
What is learning?
A changed behavioural response to a repeated stimulus
What is an example of behavioural response?
Rat doing water-maze
What has working with bees have shown?
Learning in in-vertebrates
Why can bees learn?
- Excess of a million neurons
What are the types of “simple” learning?
- Habituation
- Sensitisation
- Associative learning
What are simple learning?
Implicit or declarative types of learning
What has Eric Kandel pioneered the use of?
Aplysia
Model system for studying molecular and cellular mechanisms of learning and memory
What was Eric Kandel awarded?
- Nobel prize for Physiology or medicine in 2000
2. Mechanism of synaptic plasticity
What has been used as an experimental system?
Common snail
Why are invertebrates useful as model systems in neurobiology?
- Simple nervous system comprised of several thousand neurons
- Neuronal stomata are often large and can be repeatedly identified
- Can link physiology of individual neurons to whole-animal behaviour
What is neuronal somata?
Have neurons with large cell bodies
What does leech neuron have?
Large dendritic branch
Processes extending into nerves
What will individual ganglion contain?
Several hundred neurons
What is possible to identify?
Same neuron from individual-individual in same location
How can you confirm the same neuron?
Characterising it’s properties
What can you achieve in simpler nervous system?
Link individual neurons to individual physiological processes
How does it lead to changes in behaviour
Why is aplysia good?
- Learn about its anatomy and its nervous system
What does nervous system have?
Cluster of Ganglia around the esophagus
What is the size in diameter of cell body in brain
10 microns in diameter
How can you identify cells from individuals to individuals?
Based on relative size, coloration and positions
How can you differentiate smaller cell bodies?
Do some injections with electrodes into multiple cells
What was Kendal able to map out?
- Abnormal ganglion in some detail
2. Started to give names/numbers to individual neurons
How can you achieve individual identity?
- Recording from neurons
2. Characterising them
Experiment - sensory neurons in Aplysia
- The experimenter would place electrode in different cells of ganglion and touching body surface with mechanical stimulus to see whether any neurons would respond to touch
How can AP be fired in the neuron
- Record neuron in abdominal ganglion
2. Mechanical stimulus delivered to gill/skin under mantle
What is the correlation?
As the strength of stimulus increases, the number of AP also increases
What did functional maps of animals reveal ?
Sensory neurons responsive to touch in part of animal
What has been determined using electrophysiology?
Connection between neuron and 2 post-synaptic targets
What does stimulus to L10 neuron give?
Rise to both r15 neuron and L3 neuron
What do you see in R15?
Depolarisation
EPSP
What do you see in L3 neuron?
Hyperpolarisation
How can one neuron lead to depolarisation and hyperpolarisation ?
Receptors activated by ACH that can either be Na+ channels or Cl- channels
Nicotinic receptors
- Cartoon channels
2. Responsible for depolarisation
What has been discovered in C.elegans drosophila?
- There are ACH cl- channels
What is learning?
- Change in behaviour in response to environmental stimulus
What is the full-withdrawal reflex in Aplysia?
- Involuntary, defensive reflex
2. The reflex causes the delicate siphon and gill to be retracted when the animal is disturbed
Why did Eric Kandel exploit the gill-withdrawal reflex of Aplysia?
- Study the molecular and cellular mechanism of three types of learning
- Habituation
- Sensitisation
- Associative learning
What is Habituation?
- Decrease in behavioural response that occurs during repeated presentation of a stimulus
- Lessening of a response due to repeated stimulus
In the context of gill-withdrawal reflex what did Kandal observe?
- Large contraction of the gill
2. Able to record this with a device (photo-cell) the size of the contraction observed
Why is the marine snail Aplysia californica well suited for investigations?
- Investigations of cellular and molecular basis of behaviour
- Neuronal circuitry underlying a specific behaviour could be easily determined
- Individual components of the circuitry could be easily manipulated
What does the Aplysia nervous system contain?
Approx 20,000 neurons
Organised into 9 different Ganglia
What can the large neurons of Aplysia be easily identified based on?
- Size
- Electrical properties
- Position in the Ganglia
What does Aplysia have?
- Rich repertoire of behaviours that can be studied
What is one of the well-studied behaviours of Aplysia?
- Gill-withdrawal reflex
What are the central component of this reflex situated in?
- Abdominal Ganglia
What has components of the GWR circuitry being mapped able to show?
- Contribution of various components determined
What does GWR circuitry undergo?
- Associative and non-associative learning
What was the several different preparation of Apylasia?
- Intact animal
- Semi-intact preparation
- Reconstitution of major components of neural circuitry
What can changes in behaviour be?
- Long term
2. Short term
Long term changes in habituation
Involved structural changes in the nervous system
LTP
Increase in number of dendritic spine
LTD
Decrease in number of dendritic spine
Experiment done on individual animals
- Ganglia recorded from
- Changes are observed
- Ganglia taken out and fixed
- Sectioned and looked down at microscope
What does more recent research indicate?
- Long term habituation also involves post-synaptic mechanism
What are the changes that occur in short term habituation due to?
Metabolic nature
Hebbs postulate - metabolic changes
Change in activity of proteins at the synapse
What is sensitisation?
- Enhancement of a reflex response by the introduction of a strong or noxious stimuli
Sensitisation can be short term or long term depending on what?
- Duration/magnitude of sensitising stimulus
