Hippocampal Structure and Function
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Questions and Answers

Which of the following statements accurately describes the function of the dentate gyrus in the hippocampus?

  • The dentate gyrus receives input from the entorhinal cortex and projects to the CA3 region. (correct)
  • The dentate gyrus is responsible for the formation of new memories and the consolidation of existing memories.
  • The dentate gyrus plays a role in regulating emotional responses and stress levels.
  • The dentate gyrus receives input from the CA3 region and projects to the CA1 region.

    • Which of the following is NOT a characteristic of Long-Term Potentiation (LTP)?

  • LTP is associated with a rapid induction phase and a long-lasting maintenance phase.
  • LTP can be induced by weak stimulation of a pathway if it is paired with strong stimulation of another pathway. (correct)
  • LTP is specific to a particular pathway, meaning it only affects the synapses that were strongly activated.
  • LTP requires simultaneous activation of presynaptic and postsynaptic neurons, adhering to Hebb's rule.

    • What is the role of NMDA receptors in the induction of LTP?

  • NMDA receptors act as coincidence detectors, allowing calcium influx only when the presynaptic neuron is releasing glutamate and the postsynaptic neuron is depolarized. (correct)
  • NMDA receptors directly activate protein kinases, leading to phosphorylation of downstream targets.
  • NMDA receptors are responsible for the long-term maintenance of LTP by increasing the number of AMPA receptors at the synapse.
  • NMDA receptors are responsible for the release of neurotransmitters from the presynaptic neuron.

    • Which of the following statements accurately describes the role of CA3 pyramidal neurons in the trisynaptic circuit?

    <p>CA3 pyramidal neurons receive input from the dentate gyrus and project to the CA1 region via Schaffer collaterals. (C)</p> Signup and view all the answers

    Which of the following statements accurately describes the relationship between the CA1 region and the Schaffer collaterals?

    <p>Schaffer collaterals originate in the CA3 region and project to the CA1 region. (C)</p> Signup and view all the answers

    What is the primary consequence of sustained low-frequency stimulation in relation to synaptic function?

    <p>Induction of long-term depression (LTD) (D)</p> Signup and view all the answers

    Which of the following accurately describes the relationship between Ca2+ influx and LTP?

    <p>LTP is dependent on short bursts of high Ca2+ influx. (C)</p> Signup and view all the answers

    What role do protein synthesis inhibitors play in LTP?

    <p>They block the maintenance of LTP. (B)</p> Signup and view all the answers

    What is an engram in the context of hippocampal function?

    <p>A collection of synapses that encode specific memories. (C)</p> Signup and view all the answers

    What distinguishes long-term potentiation (LTP) from long-term depression (LTD) in terms of synaptic stimulation paradigms?

    <p>LTP is induced by short high-frequency stimulation, while LTD is due to prolonged low-frequency stimulation. (D)</p> Signup and view all the answers

    Flashcards

    LTP (Long-Term Potentiation)

    A long-lasting enhancement in synaptic strength following high-frequency stimulation.

    AMPA Receptors

    Glutamate receptors that mediate fast synaptic transmission and are inserted during LTP.

    LTD (Long-Term Depression)

    A long-lasting decrease in synaptic strength due to low-frequency stimulation.

    Role of Ca2+ in LTP

    High influx of calcium ions triggers activation of pathways that strengthen synapses.

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    Hippocampal Engrams

    Synaptic structures that encode memories through plasticity, made of connected neuron ensembles.

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    Hippocampus structure

    The hippocampus consists of a trisynaptic circuit involving input from the entorhinal cortex, granule cells in the dentate gyrus, CA3 region, and CA1.

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    Long-Term Potentiation (LTP)

    LTP is the strengthening of synapses based on their recent activity, leading to improved memory formation.

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    Hebb's Rule

    Hebb's Rule states that if an axon of cell A is near enough to excite cell B, changes both occur to increase efficiency.

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    Associative LTP

    Associative LTP occurs when weak synaptic stimulation paired with strong stimulation results in strengthened connections.

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    Study Notes

    Hippocampal Structure and Function

    • The hippocampus, found in all mammalian orders, possesses a trisynaptic circuit with three excitatory synaptic stations.
    • Input arrives from the perforant path (entorhinal cortex axons), projecting to granule cells (dentate gyrus).
    • This path leads to the CA3 region via mossy fibers.
    • Then, Schaffer collaterals connect CA3 to CA1.
    • Other brain areas also have connections.
    • Granule cells (dentate gyrus) and pyramidal neurons (CA3, CA1) are key components.
    • CA3 has complex spines and projects to CA3/CA2 (associational) or CA1 (Schaffer collateral).
    • CA1's stratum radiatum houses Schaffer collateral synapses with normal spines.
    • This circuit is well-suited to spatial navigation, integrating context and content.
    • Interneurons, including 21 types in CA1, provide crucial inhibition.

    Synaptic Plasticity (LTP & LTD)

    • Synaptic plasticity involves changing synaptic strength (e.g., Long-Term Potentiation and Long-Term Depression).
    • Hebbian learning: Repeated activation strengthens connections (synaptic efficiency increase). Information encoding must synchronize with memory timescales.
    • LTP (Long-Term Potentiation): Repeated strong activation of a synapse increases its strength. This is
      • Specific: to a pathway.
      • Fast: Induction occurs rapidly (seconds to minutes), sustained for hours.
      • Coincidence-dependent: Synaptic activity must occur simultaneously (Hebb's rule).
      • Associative LTP: Weak stimulation on one pathway can induce LTP in a different pathway if paired with strong stimulation in the first one (Pavlovian conditioning).
    • LTP Mechanisms:
      • NMDA receptors: act like coincidence detectors. Strong depolarization (high activity) removes Mg2+ blockage of NMDA channels.
      • Ca2+ influx activates signal cascades (protein kinases like CAMKII and PKC).
      • CAMKII phosphorylates downstream targets, enhancing AMPA receptor sensitivity.
      • More AMPA receptors are inserted into the synapse.
    • Maintenance of LTP: Requires synthesis of new proteins (LTP lasts hours). Blocking protein synthesis disrupts lasting LTP.
    • LTD (Long-Term Depression): Weak or infrequent synaptic activity weakens synaptic strength.
      • NMDA-dependent: Postsynaptic Ca2+ influx plays a role.
    • LTD is driven by sustained low-level Ca2+ influx. Lower Ca2+ influx activates protein phosphatases, removing AMPA receptors.
    • LTP and LTD Balance: High-frequency LTP and prolonged low-frequency LTD are unlikely in a physiological setting, as these require specific stimulation protocols.

    Hippocampus and Memory

    • Hippocampal Engrams: Synaptic plasticity forms memory engrams, ensembles of synaptically connected cells encoding specific memories.

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    Description

    Explore the intricate details of hippocampal structure, including its trisynaptic circuit and synaptic connections. Learn about the roles of key components such as granule cells and pyramidal neurons in spatial navigation and memory. This quiz will test your understanding of how the hippocampus contributes to various brain functions.

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