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Lecture 17

CSB332H1 Lecture Notes - Lecture 17: Aplysia Gill And Siphon Withdrawal Reflex, Supplementary Motor Area, Primary Motor Cortex

Cell and Systems Biology
Course Code
Francis Bambico

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Slide 13
Explicit memory information that you can recall
Implicit memory can’t really tell another person using in a narrative form but you can show through seq of motor output
o Associative (classical and operant conditioning)
o Non-associative memory: 2 types: habituation and sensitization
These are served by reflex pathways in the spinal cord
Motor behaviours
Brain mapping the diff parts that subserves diff kinds of memories
Semantic memory and episodic memory are subserved/processed in the medial, temporal lobe including hippo and parts of
the diencephalon
Procedural -> motor related structure: basal ganglia, cerebellum , primary motor area and supplementary motor area
Working memory prefrontal cortex
Habituation and sensitization
We’ve all experienced it
Sensitization: increase in response to a naturally weak stimulus after being presented with a strong stimulus
o Eg. doctor’s office for vaccination
Habituation: decline in the response after repeated exposure to the same stimulus
o Not so meaningful stimulus and your response declines progressively
Invertebrate models used to find molecular mechanisms
Popular model: aplysia (sea slug)
Neuroscientists have focused on a reflex behaviour: siphon/gill withdrawal reflex
Touch parts of the aplysia -> siphon and gill are sensitive -> structures get internalized
Mediated by a simple circuit: sensory neuron innervates the motor neuron responsible for the withdrawal
Habituation: decline in response to a stimulus after repeated exposure
Organism learns to ignore the stimulus
Evolutionary significance? Don’t waste energy on irrelevant stimuli
Gill will withdraw; respond strongly;
After several exposures to this not so strong stimulus, you will eventually lead to a decrease in the quantities of
neurotransmitters being released in the terminals
Mechanism for the decrease? Not fully explained yet
o One: inactivation of Ca channels (usually follows a time course) -> decrease of nt -> decrease in reaction
In vertebrates, such as frogs, you can electrophysiogically demonstrate how habituation happens
These researchers used a piece of muscle from the frog and bathed it in high conc of Ca and then measured the changes in
end plate potential of the muscle in response to repeated stimulation
B -> example of what happens in habituation -> synaptic depression
Initially stimulate muscles -> high amplitude
Stimulate again, you can see it progressively decrease
This decrease in end plate potential can stay for long periods of time, a max of 10s
Sensitization: increase in the response to a gentle stimulus after exposure to a strong stimulus (like electric shock)
What happens in the circuitry is more complicated than habituation
Intracellular events progress
Illustration of diff parts of the aplysia
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