Neurotransmitter Release and Calcium Ions
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Questions and Answers

What is the primary role of calcium ions ($Ca^{++}$) in neurotransmitter release?

  • To bind to ligand-gated channels on the postsynaptic membrane.
  • To initiate the synthesis of neurotransmitter molecules.
  • To promote the exocytosis of neurotransmitter vesicles. (correct)
  • To directly alter the membrane potential of the presynaptic terminal.

    • How does measuring the capacitance of the terminal membrane relate to synaptic transmission?

  • Capacitance increase is a physiological measure of exocytosis. (correct)
  • Capacitance decrease indicates neurotransmitter synthesis.
  • Capacitance decrease is directly proportional to the influx of $Ca^{++}$ ions.
  • Capacitance increase reflects endocytosis.

    • Which of the following is directly involved in regulating neurotransmitter release at the synapse?

  • Sodium-potassium pump
  • Voltage-gated $Ca^{++}$ channels (correct)
  • Acetylcholinesterase in the synaptic cleft
  • Ligand-gated ion channels on the postsynaptic membrane

    • Lambert-Eaton myasthenic syndrome (LEMS) is associated with an autoimmune attack on which component of synaptic transmission?

    <p>Voltage-gated $Ca^{++}$ channels (B)</p> Signup and view all the answers

    In chemical synaptic transmission, what event immediately precedes the influx of $Ca^{++}$ ions into the presynaptic terminal?

    <p>Arrival of a presynaptic action potential (D)</p> Signup and view all the answers

    What is the primary role of Calcium (Ca++) channels in neurotransmitter release?

    <p>To trigger vesicle fusion and exocytosis of neurotransmitters. (D)</p> Signup and view all the answers

    What does the observation of miniature end plate potentials (mEPPs) even in the absence of a presynaptic action potential suggest?

    <p>There is spontaneous, quantized release of neurotransmitter independent of presynaptic action potentials. (D)</p> Signup and view all the answers

    How are end plate potentials (EPPs) related to miniature end plate potentials (mEPPs)?

    <p>EPPs are summated mEPPs, reflecting multi-vesicular neurotransmitter release. (C)</p> Signup and view all the answers

    What is the significance of the prolonged inward Calcium current (ICa)?

    <p>It contributes to the sustained depolarization and facilitates neurotransmitter release. (C)</p> Signup and view all the answers

    What is the jellyfish aequorin protein used for in neurophysiological studies?

    <p>To measure presynaptic calcium levels during depolarization. (B)</p> Signup and view all the answers

    What is the primary function of Cl- channels in the context of inhibitory currents?

    <p>Opposing excitatory potentials (A)</p> Signup and view all the answers

    Where are neuropeptides synthesized within a neuron?

    <p>Cell body (B)</p> Signup and view all the answers

    Which type of amine neurotransmitter is derived from aromatic amino acid precursors?

    <p>Biogenic amines (B)</p> Signup and view all the answers

    Which process is targeted by Selective Serotonin Reuptake Inhibitors (SSRIs)?

    <p>Re-uptake of serotonin by neurons (D)</p> Signup and view all the answers

    What is the role of monoamine oxidase inhibitors (MAOIs)?

    <p>Blocking the breakdown of biogenic amines (D)</p> Signup and view all the answers

    What distinguishes chemical synapses from electrical synapses?

    <p>All of the above. (D)</p> Signup and view all the answers

    What kind of post-synaptic receptors are present at chemical synapses?

    <p>Ligand-gated channels (B)</p> Signup and view all the answers

    What is the primary neurotransmitter at the neuromuscular junction (NMJ)?

    <p>Acetylcholine (D)</p> Signup and view all the answers

    Which neurotransmitter is typically associated with inhibitory synapses in the CNS?

    <p>Glycine (A)</p> Signup and view all the answers

    What is GABA short for?

    <p>Gamma-Aminobutyric Acid (D)</p> Signup and view all the answers

    Which toxins were used to identify pre- and post-synaptic membrane proteins at the NMJ?

    <p>Spider and cobra toxins (D)</p> Signup and view all the answers

    What microscopic technique provided evidence for exocytosis during neurotransmission?

    <p>Transmission electron microscopy (C)</p> Signup and view all the answers

    What is the term for the specialized synapse region of the neuromuscular junction?

    <p>End plate (A)</p> Signup and view all the answers

    What type of receptor is the nicotinic acetylcholine receptor?

    <p>Ionotropic receptor (D)</p> Signup and view all the answers

    What is the role of acetylcholinesterase (AchE) in the synaptic cleft?

    <p>Breaks down acetylcholine (D)</p> Signup and view all the answers

    What change in membrane potential is characteristic of an excitatory postsynaptic potential (EPSP)?

    <p>Depolarization (C)</p> Signup and view all the answers

    Which ion channels are typically involved in inhibitory postsynaptic potentials (IPSPs)?

    <p>Cl- or K+ channels (B)</p> Signup and view all the answers

    Which neurotransmitter is a major target in myasthenia gravis therapy and for pesticides?

    <p>Acetylcholine (A)</p> Signup and view all the answers

    What type of receptor is opened by glutamate and a positive change in membrane voltage (+VM)?

    <p>NMDA receptor (D)</p> Signup and view all the answers

    What is the primary inhibitory neurotransmitter in the central nervous system (CNS)?

    <p>GABA (B)</p> Signup and view all the answers

    Which neurotransmitter is synthesized from glutamate?

    <p>GABA (B)</p> Signup and view all the answers

    Flashcards

    Ca++ as Ion

    Calcium ions (Ca++) are crucial for exocytosis in cells.

    Exocytosis vs Endocytosis

    Exocytosis increases membrane capacitance, while endocytosis decreases it.

    SNARE Complex

    Proteins facilitating the fusion of synaptic vesicles with the membrane.

    Botulinum Toxin

    A toxin that interferes with SNARE proteins, affecting neurotransmitter release.

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    Myasthenia Gravis

    An autoimmune disorder targeting calcium channels, impairing muscle contractions.

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    Cl- channels

    Ion channels that allow chloride ions to flow, inhibiting excitatory currents.

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    Neuropeptides

    Short proteins synthesized in the cell body that act as neurotransmitters or modulators.

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    Biogenic amines

    Neurotransmitters derived from aromatic amino acids, including dopamine and serotonin.

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    Dueling neuropeptides

    Neuropeptides like substance P and enkephalin involved in the pain pathway.

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    SSRI (Selective Serotonin Reuptake Inhibitors)

    Medications that block the reuptake of serotonin, increasing its availability in the brain.

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    mEPPs

    Miniature end plate potentials are graded potentials resulting from the release of a single vesicle of neurotransmitter.

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    EPP

    End plate potentials are the NMJ equivalent of excitatory post-synaptic potentials (EPSPs) resulting from mEPP summation.

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    Calcium's role

    Increased pre-synaptic Ca++ is required for the release of transmitters during strong depolarization.

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    Action potential

    An action potential (AP) triggers the opening of voltage-gated Ca++ channels in the pre-synaptic terminal.

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    Voltage-dependent calcium dyes

    Dyes like fura-2 are used to image Ca++ in studies of dendritic spines, important for synaptic transmission research.

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    Synaptic Transmission

    The process of sending signals between neurons via neurotransmitters.

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    Neurotransmitters

    Chemicals that transmit signals across synapses.

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    Chemical Synapses

    Common type of synapse that requires neurotransmitters to transmit signals.

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    Electrical Synapses

    Rare synapses allowing direct electrical flow between neurons.

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    Ligand-gated Channels

    Receptors on the post-synaptic membrane that open in response to neurotransmitters.

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    Acetylcholine (Ach)

    An excitatory neurotransmitter primarily found in the neuromuscular junction.

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    GABA

    An inhibitory neurotransmitter also known as Gamma Amino Butyric Acid.

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    Exocytosis in Neurotransmission

    Process where neurotransmitters are released from vesicles into the synaptic cleft.

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    Nicotinic Acetylcholine Receptor

    A type of ligand-gated ionotropic receptor that responds to acetylcholine, involved in fast neurotransmission.

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    Ligand-gated Ionotropic Receptor

    Receptors that open in response to a specific neurotransmitter, leading to rapid ion flow across membranes.

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    Excitatory Post Synaptic Potential (EPSP)

    A graded potential that makes the postsynaptic membrane more likely to fire an action potential by depolarizing it.

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    Inhibitory Post Synaptic Potential (IPSP)

    A graded potential that makes the postsynaptic membrane less likely to fire an action potential by hyperpolarizing it.

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    Acetylcholine

    A neurotransmitter crucial for muscle activation and neurocommunication, synthesized by choline acetyltransferase.

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    Acetylcholinesterase (AchE)

    An enzyme that breaks down acetylcholine in the synaptic cleft, terminating its action.

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    Glutamate

    The major excitatory neurotransmitter in the CNS, crucial for synaptic plasticity and memory.

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    Study Notes

    Synaptic Transmission

    • Synaptic transmission involves chemical and electrical transmission.
    • Morphological studies examine the structure of synapses.
    • Physiological studies investigate the function of synapses.

    Neurotransmitters

    • Acetylcholine (ACh), amino acids, amines, and peptides are neurotransmitters.
    • ACh, amino acids (like glutamate and GABA), amines (like dopamine and serotonin), and peptides are neurotransmitters.
    • Neurotransmitters' uptake and termination processes are crucial.
    • Pharmacology research studies the effects of drugs on neurotransmitters.
    • Neurotransmitters like acetylcholine (ACh) are crucial for neuromuscular activity.
    • Botulinum toxin and tetanus toxin affect SNARE proteins, which affect synaptic transmission.
    • Neurotransmitters are released by exocytosis.
    • Specific receptors for neurotransmitters, like the nicotinic ACh receptor, are targeted by various toxins.

    Chemical Synapses

    • Chemical synapses are common and use neurotransmitters to transmit signals across a 200 nm gap between the presynaptic and postsynaptic neurons.
    • Chemical synapses rely on chemical neurotransmitters to signal across the synapses.
    • Chemical synapses have receptors for these neurotransmitters on the postsynaptic neuron.
    • Ligand-gated ion channels or ionotropic receptors are postsynaptic receptors involved in chemical signaling.
    • The neuromuscular junction (NMJ) uses acetylcholine (ACh) as a neurotransmitter.

    Electrical Synapses

    • Electrical synapses are rare and allow direct electrical signal flow for fast transmission across a 20-nanometer gap.
    • Electrical synapses use connexons.
    • Connexons are protein channels that allow direct electrical signal transmission.

    Synaptic Morphology - Neuromuscular Junction (NMJ)

    • Immunochemistry methods are used to identify pre- and post-synaptic membrane proteins.
    • The neuromuscular junction (NMJ) is a synapse between a motor neuron and a muscle fiber.
    • The NMJ involves pre-synaptic axon terminals and post-synaptic muscle fiber structures.
    • Spider and cobra toxins affect pre- and post-synaptic receptor proteins at the NMJ respectively.

    Morphological Evidence for Exocytosis During Neurotransmission

    • TEM (transmission electron microscopy) and SEM (scanning electron microscopy) studies are used to examine vesicle release.
    • Omega figures ($\Omega$) are observations from the fusion of vesicle and membrane during exocytosis.
    • Freeze fracture techniques aid in observing membrane structures.

    Physiological View of Exocytosis

    • Miniature end-plate potentials (mEPPs) are small, spontaneous depolarizations of the post-synaptic membrane.
    • Miniatures represent the fundamental unit of synaptic transmission.
    • End-plate potentials (EPPs) are larger depolarizations, summations of mEPPs.
    • Exocytosis relates graded potentials (mEPPs) to vesicle release of neurotransmitter.

    Jellyfish Aequorin Protein - Bioluminescent Ca++ signal

    • Jellyfish aequorin protein is bioluminescent, allowing the measurement of Ca++ influx during pre-synaptic depolarization.
    • The influx of Ca++ triggers transmitter release.

    Ca++ Channels Regulate NT Release

    • The arrival of an action potential depolarizes the presynaptic terminal, opening voltage-gated Ca++ channels.
    • Increased Ca++ concentration inside the presynaptic terminal triggers neurotransmitter release via exocytosis.
    • Ca++ plays a significant role in the regulated release of neurotransmitters.

    Exocytosis and Endocytosis

    • Capacitance measurements monitor membrane area changes during exocytosis and endocytosis.
    • Exocytosis increases membrane capacitance, and endocytosis decreases it.
    • Exocytosis can occur in two forms: classical and "kiss-and-run".

    SNARE Complex

    • SNARE complex proteins regulate synaptic vesicle fusion with the presynaptic membrane.
    • These proteins comprise the membrane fusion process.

    Toxins Affecting Ca Mechanism

    • Botulinum toxin and tetanus toxin affect neurotransmitter release through targeting SNARE proteins.

    Neurotransmitters: 1. Acetylcholine

    • Acetylcholine (ACh) is synthesized by Choline acetyltransferase (ChaT).
    • Acetylcholinesterase (AChE) breaks down ACh in the synaptic cleft.
    • ACh uptake and reuse are critical in synaptic function.

    Glutamate - Major CNS Excitatory Transmitter

    • Glutamate activates AMPA and NMDA receptors, leading to postsynaptic excitatory potentials (EPSPs).

    Amino Acid Transmitters

    • GABA is a major inhibitory neurotransmitter in the CNS.
    • Glycine is another inhibitory neurotransmitter in the CNS.
    • GABA and glycine open chloride channels, which lead to inhibitory postsynaptic potentials (IPSPs).

    Neuropeptides

    • Neuropeptides act as both neurotransmitters and neuromodulators.
    • They are involved in slow, sustained responses compared to classical neurotransmitters.
    • These peptides are synthesized in the cell body and transported to terminals.

    Biogenic Amines

    • Biogenic amines like dopamine, norepinephrine, serotonin, and histamine are synthesized from aromatic amino acids.
    • These neurotransmitters play diverse roles in the nervous system.

    Uptake and Synthesis of NTs

    • Neurotransmitter removal from the synapse is crucial.
    • Glial cells and neurons participate in reuptake processes.
    • Enzymes like monoamine oxidase (MAO) break down neurotransmitters, affecting neurotransmitter function in neurons.

    Enzymatic Breakdown of Amines

    • Monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) are enzymes that break down amines like dopamine and norepinephrine.

    Pharmacological Intervention at Aminerrgic Synapses

    • Various drugs target processes like dopamine synthesis, dopamine reuptake, or adrenergic receptor activation for therapeutic purposes.
    • Specific neurotransmitter systems are targeted via drugs for various conditions.

    Myasthenia Gravis

    • Myasthenia gravis is an autoimmune disorder affecting neuromuscular transmission.
    • Myasthenia gravis results in the degeneration of acetylcholine (ACh) receptors.

    Ligand-Gated Ionotropic Receptors

    • Ionotropic receptors are receptors linked to ligand-gated ion channels.
    • Transmembrane depolarization and hyperpolarization are induced by excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs).
    • Ligand-gated ion channels mediate fast neurotransmission.

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    Description

    This quiz explores the critical role of calcium ions in neurotransmitter release at synapses. It covers various mechanisms, including the measurement of membrane capacitance and the implications of miniature end plate potentials. Test your understanding of synaptic transmission and the factors influencing it.

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