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What is the primary response change that occurs during habituation?
Which organism is commonly used as a model for studying learning and memory through habituation?
What is the main effect on the sensory neuron during the habituation process?
Which neurotransmitter is released by interneurons during the sensitization process?
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What role does cyclic AMP (cAMP) play in the sensitization process?
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What occurs to EPSPs in the gill-withdrawal reflex during habituation?
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During sensitization, which process contributes to the prolonged action potential in the sensory neuron?
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Which cellular response is linked to the CREB protein during sensitization?
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What is the significance of the reduction in Ca2+ influx during habituation?
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In the gill-withdrawal reflex, what is the consequence of a shock applied to the tail during sensitization?
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What is a key characteristic of the model organism Aplysia for studying learning and memory?
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During habituation, the action potentials in sensory neurons change significantly.
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What is the process called that enhances the stimulus response following exposure to a noxious stimulus?
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In the gill-withdrawal reflex, the reduction in influx of Ca2+ in response to an action potential is a result of __________.
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Match the following components with their roles in sensitization:
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Which of the following changes occur during sensitization in the gill-withdrawal reflex?
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EPSPs are reduced throughout the process of habituation.
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What is the main neurotransmitter involved in facilitating the response during sensitization?
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What contributes to the increase in neurotransmitter release during sensitization?
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Which mechanism is primarily responsible for the reduction of EPSPs during habituation?
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What role does the interneuron play during sensitization in the gill-withdrawal reflex?
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Which of the following accurately describes a change that occurs in the sensory neuron during sensitization?
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How does calcium ion influx change during habituation compared to sensitization?
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What effect does CREB activation have during the sensitization process?
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What is the primary outcome of the reduction in intracellular Ca2+ during habituation?
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In the gill-withdrawal reflex, what is the effect of the shock applied to the tail?
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Study Notes
Habituation
- The weakening of a stimulus response due to repeated presentations of a neutral stimulus.
- A reductionist approach to studying learning suggests that there are conserved features in the mechanisms of learning that can be studied even in simple invertebrate animals, like the Aplysia.
- Aplysia is a useful model organism for studying learning and memory
- It has the largest nerve cells of any known animal.
- It has a small number of neurons (~20,000) making it easier to study.
- Its neuroanatomy is extremely stable (similar neuronal layout).
- Simple behavior of the Aplysia can be studied:
- The gill-withdrawal reflex is a good example to study learning.
- If the Aplysia is repeatedly exposed to a water jet stimulus, the gill will withdraw less and less (less contraction).
- The action potentials in the sensory neuron do not change before or after habituation.
- The stimulation of the motor neuron does not change before or after habituation.
- The EPSPs are reduced throughout habituation.
- The gill-withdrawal reflex is a good example to study learning.
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Summary
- There is no change in the sensory neuron’s activity.
- EPSPs are reduced during habituation.
- This is due to a reduction in the influx of Ca2+ in response to an action potential. This, in turn, leads to a reduction in the number of synaptic vesicles available for neurotransmitter release at the terminals. Consequently, less neurotransmitter is released into the synapse leading to less depolarization of the post-synaptic neuron.
Sensitization
- Sensitization is an enhanced stimulus response following single or multiple exposures to a noxious stimulus.
- In Aplysia, the gill-withdrawal reflex can be used to study sensitization:
- A shock to the tail of an Aplysia (sensory neuron) creates an action potential that travels to the interneuron (shocked once)
- This leads to increased EPSPs (excitatory postsynaptic potential).
- The process:
- The shock sent to the sensory neuron (S) creates an action potential (AP).
- The AP travels to the interneuron which releases serotonin.
- Serotonin (5-HT) is then taken up by the 5-HT receptor (5-HTR) on the S neuron.
- In the S neuron:
- The binding of 5-HT to the 5-HTR activates adenylyl cyclase.
- Adenylyl cyclase then turns ATP into cyclic AMP (cAMP)
- cAMP activates Protein Kinase A (PKA).
- PKA phosphorylates the K+ channels, which changes their conformation and makes them smaller.
- The smaller K+ channels allow fewer K+ ions to leave the cell, which prolongs the action potential.
- The longer action potential allows more Ca2+ to enter the cell through voltage-gated channels.
- Increased Ca2+ helps the synaptic vesicles move to the presynaptic terminal and release more neurotransmitter into the synaptic cleft.
- The neurotransmitter (e.g., glutamate) is then taken up by the glutamate receptor in the motor neuron.
- PKA also triggers the production of CREB (crucial for transcription), which leads to the production of more mRNA.
- This ultimately leads to the production of more proteins and the creation of new synapses.
- CREB also triggers the production of ubiquitin hydrolase, which in turn leaves PKA active (by preventing its degradation) and leads to the release of more neurotransmitter (e.g., glutamate) into the synapse.
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Summary
- Sensitization involves the role of interneurons.
- The release of serotonin by interneurons, via second messengers, leads to:
- G-protein activation, dissociation and binding to adenylyl cyclase.
- Production of cAMP (from ATP), which binds and liberates to PKA to phosphorylate ion channels.
- Reduced efflux of potassium ions.
- Increased influx of calcium ions.
- Increased release of neurotransmitter.
- Enhanced synaptic transmission and sensitization.
Habituation
- Definition: A decrease in a response to a stimulus after repeated presentations.
- Reductionist approach: Studies simple organisms to understand complex behaviors.
- Aplysia: A sea slug that serves as a model organism for studying learning and memory because of its large, easily identifiable neurons.
- Gill-withdrawal reflex: Aplysia withdraws its gill in response to a waterjet stimulus.
- Habituation in the gill-withdrawal reflex: The gill withdrawal response weakens after repeated waterjet stimuli.
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Neural mechanisms of habituation:
- No change in activity in the sensory neuron.
- Reduced excitatory postsynaptic potentials (EPSPs):
- Decreased calcium influx during action potentials.
- Fewer synaptic vesicles released.
- Less neurotransmitter in the synapse.
- Less depolarization of the postsynaptic neuron.
Sensitization
- Definition: Enhancement of a response to a stimulus following exposure to a noxious stimulus.
- Sensitization in the gill-withdrawal reflex: A tail shock leads to an increased gill withdrawal response.
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Neural mechanisms of sensitization:
- Interneuron release of serotonin:
- Serotonin activates G-protein coupled receptors (5-HTR) on sensory neurons.
- Second messenger cascade:
- Activated G-proteins trigger adenylyl cyclase.
- Adenylyl cyclase converts ATP to cyclic AMP (cAMP).
- cAMP activates protein kinase A (PKA).
- PKA phosphorylation:
- PKA phosphorylates potassium channels, causing them to close.
- This prolongs the action potential in the sensory neuron.
- More calcium enters the sensory neuron, leading to increased neurotransmitter release.
- Interneuron release of serotonin:
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Long-term changes:
- PKA triggers the production of cAMP response element binding protein (CREB).
- CREB promotes gene transcription for new proteins and synapses.
- PKA also activates ubiquitin hydrolase, which prevents PKA degradation, leading to sustained neurotransmitter release.
- The role of interneurons: Interneurons mediate the sensitization response by releasing serotonin.
Habituation
- A decrease in the strength of a response to a stimulus due to repeated exposure.
- Can be observed in simple organisms, like the Aplysia (sea slug).
- Aplysia has a simple nervous system, making it an ideal model to study the cellular mechanisms of learning.
- The gill-withdrawal reflex in Aplysia is a well-studied example of habituation.
- Repeated water jet stimulation results in a decrease in the gill withdrawal response.
- While the sensory and motor neurons involved remain unchanged, the strength of the EPSPs is reduced.
- Reduced EPSPs are attributed to a decrease in calcium influx, leading to fewer synaptic vesicles being released and ultimately less neurotransmitter in the synapse.
Sensitization
- An enhancement of a response to a stimulus after exposure to a noxious stimulus.
- Also demonstrated in the Aplysia's gill-withdrawal reflex.
- A shock to the Aplysia's tail (sensory neuron) triggers a serotonin release from an interneuron.
- Serotonin binds to receptors on the sensory neuron activating a cascade of signaling events.
- Adenylyl cyclase is activated, leading to cAMP production.
- cAMP activates PKA which phosphorylates K+ channels, leading to a longer action potential.
- The longer action potential allows more calcium influx.
- Increased calcium influx leads to more neurotransmitter release from the sensory neuron.
- PKA also activates CREB protein, leading to more protein synthesis, including synaptic proteins, and ultimately, new synapse formation.
- Additionally, the activated ubiquitin hydrolase maintains PKA activity, further amplifying the effects of sensitization.
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Description
Explore the concept of habituation through the study of the Aplysia model organism. This quiz examines the mechanisms of learning, specifically the gill-withdrawal reflex, and how repeated stimuli affect response over time. Understand the implications for broader learning theories in both simple and complex organisms.
