Podcast
Questions and Answers
How does monocular deprivation during the critical period impact the formation of ocular dominance columns (ODCs)?
How does monocular deprivation during the critical period impact the formation of ocular dominance columns (ODCs)?
- It accelerates the maturation of ODCs, resulting in earlier binocular vision.
- It enhances the segregation of inputs, leading to stronger ODCs.
- It disrupts the normal formation of ODCs, potentially leading to visual impairments. (correct)
- It prevents the formation of new synapses but does not affect existing ODCs.
What is the critical requirement that sets NMDA receptors (NMDARs) apart from other glutamate receptors, enabling them to function as 'coincidence detectors' in synaptic plasticity?
What is the critical requirement that sets NMDA receptors (NMDARs) apart from other glutamate receptors, enabling them to function as 'coincidence detectors' in synaptic plasticity?
- NMDARs are exclusively located on presynaptic neurons, allowing them to directly measure glutamate release.
- NMDARs require the binding of multiple different neurotransmitters simultaneously for activation.
- NMDARs necessitate both glutamate binding and postsynaptic depolarization to be activated. (correct)
- NMDARs possess an unusually high affinity for glutamate, enabling them to detect even minuscule amounts of neurotransmitter.
If a researcher is investigating the effects of long-term potentiation (LTP) and long-term depression (LTD) on synaptic strength during development, which aspect of these processes is most crucial to consider in relation to critical periods?
If a researcher is investigating the effects of long-term potentiation (LTP) and long-term depression (LTD) on synaptic strength during development, which aspect of these processes is most crucial to consider in relation to critical periods?
- The duration of the stimulation required to induce LTP versus LTD.
- The location of LTP and LTD induction within different brain regions.
- The specific type of glutamate receptor involved in LTP and LTD.
- The correlation between the inducibility of LTP/LTD and the timing of critical periods. (correct)
Which of the following best describes the role of microglia in synaptic refinement?
Which of the following best describes the role of microglia in synaptic refinement?
In the context of stereotyped axon pruning, what distinguishes this process from activity-dependent refinement?
In the context of stereotyped axon pruning, what distinguishes this process from activity-dependent refinement?
What implications does the Hebbian learning principle – 'cells that fire together, wire together' – have for synaptic strengthening?
What implications does the Hebbian learning principle – 'cells that fire together, wire together' – have for synaptic strengthening?
How does heterosynaptic depression contribute to synaptic weakening?
How does heterosynaptic depression contribute to synaptic weakening?
How does activity-dependent competition between inputs from the two eyes influence cortical territory?
How does activity-dependent competition between inputs from the two eyes influence cortical territory?
In the context of synaptic refinement, what is the primary role of regressive events?
In the context of synaptic refinement, what is the primary role of regressive events?
What role do repulsive cues, such as PlexinA3/A4 receptors for semaphorins, play in stereotyped pruning?
What role do repulsive cues, such as PlexinA3/A4 receptors for semaphorins, play in stereotyped pruning?
Flashcards
Ocular Dominance Columns (ODCs)
Ocular Dominance Columns (ODCs)
Columns in the visual cortex representing segregated inputs from the two eyes, essential for binocular vision.
Synaptic Weakening
Synaptic Weakening
Synapses weaken when inactive or out of sync with other inputs, sometimes through heterosynaptic depression.
Synaptic Strengthening
Synaptic Strengthening
Consistently active synapses strengthen because the presynaptic neuron consistently fires the postsynaptic neuron, 'cells that fire together, wire together'.
NMDA Receptor (NMDAR)
NMDA Receptor (NMDAR)
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Coincident Input
Coincident Input
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Strengthening Co-active Inputs
Strengthening Co-active Inputs
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Long-Term Potentiation (LTP)
Long-Term Potentiation (LTP)
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Long-Term Depression (LTD)
Long-Term Depression (LTD)
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Microglia
Microglia
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Stereotyped Pruning
Stereotyped Pruning
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Study Notes
Importance of Binocular Experience and Activity
- Normal binocular experience is critical for the proper development of connections in the primary visual cortex
- Abnormal visual experiences during the critical period can disrupt ODC formation
- Inputs from the two eyes compete for cortical territory, influenced by neuronal activity
- Ocular dominance columns (ODCs) represent segregated inputs from the two eyes, essential for binocular vision
Synaptic Strengthening and Weakening: Hebbian Mechanisms
- Synaptic refinement relies on how neuronal activity shapes synaptic strength
- Synapses that are inactive or out of sync with other inputs tend to be weakened or eliminated
- Heterosynaptic depression is when stimulating one input leads to the weakening of a nearby inactive input
- Synapses that are consistently active together are strengthened
- Hebbian learning describes how cells that fire together, wire together
NMDA Receptors: Detecting Coincidence
- NMDA receptor (NMDAR) is a molecular coincidence detector
- NMDARs require both glutamate binding and postsynaptic depolarization to be activated
- When inputs to a neuron are active simultaneously, the postsynaptic neuron is more likely to be depolarized
- NMDAR activation triggers downstream signaling cascades that can lead to long-term potentiation (LTP)
LTP and LTD: Long-Term Changes
- Long-term potentiation (LTP) and long-term depression (LTD) are experimental models for studying activity-dependent synaptic plasticity
- LTP is characterized by a long-lasting increase in synaptic strength, often induced by high-frequency stimulation of presynaptic neurons
- LTD is characterized by a long-lasting decrease in synaptic strength, often induced by low-frequency stimulation of presynaptic neurons
- Both LTP and LTD are NMDAR-dependent and involve calcium influx into the postsynaptic neuron
- The timing and pattern of NMDAR activation likely determine whether LTP or LTD occurs
Microglia: Engulfing Inactive Synapses
- Microglia are active players in circuit refinement
- Microglia survey the environment and engage in phagocytosis, engulfing and removing cellular debris
- Microglia preferentially target and engulf less active synapses
Stereotyped Pruning: Predetermined Axon Removal
- Axon pruning is another form of circuit refinement
- Axon pruning can be stereotyped, meaning it follows a genetically predetermined pattern
- Repulsive cues guide the pruning of specific axon branches
- PlexinA3/A4, receptors for semaphorins, are required for the stereotyped pruning of visual corticospinal axons from the spinal cord
Summary: Sculpting Circuits through Refinement
- Regressive events, such as synapse elimination and axon pruning, refine the initial "draft" of connections
- Synaptic strength is dynamically regulated by neuronal activity
- Coincident activity strengthens connections, while asynchronous activity weakens them
- NMDARs are well-suited for detecting coincident activity
- Microglia actively participate in circuit refinement by engulfing and removing inactive synapses
- Some axon pruning events follow predetermined patterns guided by specific molecular cues
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