Neurotransmitters and Receptors Quiz
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Questions and Answers

What is the role of neurotransmitters in the postsynaptic membrane?

  • They bind to receptors and trigger a response in the postsynaptic cell. (correct)
  • They act as enzymes that break down other molecules.
  • They transport proteins across the membrane.
  • They act as voltage-gated channels that allow ions to flow across the membrane.

    • What are the two main classes of acetylcholine receptor proteins?

  • Excitatory and inhibitory
  • Ionotropic and metabotropic (correct)
  • Direct and indirect
  • Voltage-gated and ligand-gated

    • What is the role of calcium ions (Ca2+) in neurotransmitter release?

  • Ca2+ ions open voltage-gated channels, allowing neurotransmitters to bind to receptors.
  • Ca2+ ions directly trigger the release of neurotransmitters from synaptic vesicles. (correct)
  • Ca2+ ions bind to neurotransmitters, preventing their release.
  • Ca2+ ions are involved in the synthesis of neurotransmitters in the axon terminal.

    • How do neurotransmitters differ in their effects on postsynaptic cells?

    <p>Neurotransmitters can either stimulate or inhibit, depending on the receptor they bind to. (A)</p> Signup and view all the answers

    What is the function of a nicotinic acetylcholine receptor?

    <p>It acts as a sodium channel, leading to depolarization. (D)</p> Signup and view all the answers

    Which of the following processes is NOT involved in the removal of neurotransmitters from the synaptic cleft?

    <p>Release by exocytosis (C)</p> Signup and view all the answers

    What is the defining characteristic of a metabotropic receptor?

    <p>It indirectly influences the postsynaptic cell by activating a cascade of intracellular events. (D)</p> Signup and view all the answers

    Which of the following accurately describes the relationship between neurotransmitters and their receptors?

    <p>One neurotransmitter can bind to multiple different receptors, resulting in different effects. (A)</p> Signup and view all the answers

    What role does myelin play in the conduction of action potentials in myelinated axons?

    <p>It provides insulation that prevents current loss. (A)</p> Signup and view all the answers

    What is the process of conduction in myelinated axons called?

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

    How does the action potential conduction velocity in myelinated axons compare to unmyelinated axons?

    <p>It is faster in myelinated axons. (B)</p> Signup and view all the answers

    Where does the action potential begin in a myelinated axon?

    <p>At the axon hillock (A)</p> Signup and view all the answers

    What does the term 'presynaptic cell' refer to?

    <p>Neuron that sends a signal (B)</p> Signup and view all the answers

    What initiates the rising phase of an action potential?

    <p>Na+ flows into the neuron (B)</p> Signup and view all the answers

    During the falling phase of an action potential, what happens to the potassium (K+) channels?

    <p>They open and K+ flows out. (C)</p> Signup and view all the answers

    What is the role of the Na+/K+ pump during an action potential?

    <p>To maintain the concentration gradient of Na+ and K+ (D)</p> Signup and view all the answers

    What occurs immediately after the peak depolarization of an action potential?

    <p>K+ channels open and Na+ channels become inactivated (C)</p> Signup and view all the answers

    What characteristic of K+ leak channels is described in the content?

    <p>They are always open. (B)</p> Signup and view all the answers

    What is the primary mechanism that initiates the action potential rise phase?

    <p>Positive feedback from Na+ channels (D)</p> Signup and view all the answers

    During propagation along an axon, what prevents backpropagation into the soma?

    <p>Refractory period of Na+ channels (C)</p> Signup and view all the answers

    What is the primary benefit of saltatory conduction in myelinated axons?

    <p>Faster transmission of action potentials (D)</p> Signup and view all the answers

    In unmyelinated axons, what initiates the action potential in adjacent downstream segments?

    <p>Reached threshold from large depolarization (D)</p> Signup and view all the answers

    What role does the diameter of the axon play in action potential conduction speed?

    <p>Larger diameter results in faster conduction (B)</p> Signup and view all the answers

    Where does ion flow occur in myelinated axons during action potential transmission?

    <p>Only at the nodes of Ranvier (D)</p> Signup and view all the answers

    What characterizes the action potential propagation in unmyelinated axons?

    <p>Continuously across the entire membrane (A)</p> Signup and view all the answers

    What mechanism ensures that action potentials are conducted unchanged along the axon?

    <p>Unidirectional propagation due to refractory periods (D)</p> Signup and view all the answers

    What distinguishes an electrical synapse from a chemical synapse?

    <p>Direct ion transfer between cells (D)</p> Signup and view all the answers

    Which statement about neurotransmitter release at a chemical synapse is accurate?

    <p>It requires influx of Ca2+ ions. (C)</p> Signup and view all the answers

    Which function does neurotransmitter binding to postsynaptic receptors primarily serve?

    <p>Opening channels that lead to depolarization or hyperpolarization (C)</p> Signup and view all the answers

    What is the role of gap junctions in electrical synapses?

    <p>To connect the cytoplasm of presynaptic and postsynaptic cells (A)</p> Signup and view all the answers

    In an experimental setup with two hearts, what conclusion can be drawn about Heart 2's reaction?

    <p>It received chemical signals from Heart 1. (D)</p> Signup and view all the answers

    What property of chemical synapses allows integration of multiple presynaptic inputs?

    <p>Chemical nature of transmission (D)</p> Signup and view all the answers

    Which characteristic is unique to inhibitory neurotransmitters in chemical synapses?

    <p>They open channels leading to hyperpolarization. (C)</p> Signup and view all the answers

    How does the rapid flow of current in electrical synapses impact cellular responses?

    <p>It allows for synchronized activity among connected cells. (D)</p> Signup and view all the answers

    Flashcards

    Depolarization

    The process where the membrane potential becomes less negative (more positive), allowing Na+ ions to flow into the cell.

    Voltage-Gated Sodium Channels

    Channels that open in response to changes in membrane potential, allowing Na+ ions to enter the cell during the action potential.

    Falling Phase of AP

    The phase following depolarization where potassium (K+) channels open, leading to K+ flowing out and the cell becoming more negative.

    Refractory Period

    A recovery period after an action potential where the neuron cannot fire another AP; ensures unidirectional signal.

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    K+ Leak Channels

    Channels that are always open, allowing K+ ions to passively flow in and out, helping maintain resting membrane potential.

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    Myelinated Axon

    An axon surrounded by myelin insulation that speeds up action potential conduction.

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    Saltatory Conduction

    The process where action potentials jump from node to node along a myelinated axon.

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    Node of Ranvier

    Gaps in myelin where ion channels are concentrated, facilitating rapid conduction.

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    Presynaptic Cell

    The neuron that sends a signal in a synapse during communication.

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    Postsynaptic Cell

    The neuron that receives a signal in a synapse after transmission.

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    Positive Feedback in AP Rise

    A process where initial depolarization opens Na+v channels, increasing Na+ permeability.

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    Axon Hillock

    The region where action potentials are initiated due to high concentration of Na+v channels.

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    Propagation of Action Potential

    The movement of action potentials along an axon caused by ion flow depolarizing adjacent segments.

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    Unmyelinated Axon Conduction

    Action potentials are generated along the entire length of the axon, from one Na+v channel to another.

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    Refractory Period in Unmyelinated Axon

    A phase ensuring that Na+v channels can't reopen immediately, preventing backpropagation.

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    Axon Diameter Effect

    The speed of action potential conduction increases with larger axon diameters.

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    Electrical Synapse

    A type of synapse where impulses pass directly between cells through gap junctions.

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    Chemical Synapse

    A synapse where neurotransmitters are released and cross a synaptic cleft to communicate.

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    Synaptic Cleft

    The small gap separating the presynaptic and postsynaptic cells in a chemical synapse.

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    Neurotransmitter Release

    The process where vesicles containing neurotransmitters fuse with the presynaptic membrane and release their contents.

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    Postsynaptic Receptors

    Molecular structures on the postsynaptic cell that bind with neurotransmitters.

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    Depolarization via Neurotransmitters

    The effect when neurotransmitters bind to receptors, leading to cell membrane depolarization.

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    Inhibitory Neurotransmitters

    Neurotransmitters that cause hyperpolarization of the postsynaptic membrane, decreasing action potential chances.

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    Synchronous Activity

    When neurons communicate rapidly through electrical synapses, resulting in coordinated responses.

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    Binding

    The action that opens or closes the channel gate in neurons.

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    Ca2+ role in neurotransmitter release

    Ca2+ ions trigger exocytosis, leading to neurotransmitter release when action potentials arrive.

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    Acetylcholine Effects

    Acetylcholine can stimulate skeletal muscle contraction and inhibit cardiac muscle contraction via different receptors.

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    Ionotropic Receptors

    Ligand-gated ion channels that open in response to neurotransmitter binding, affecting ion current.

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    Metabotropic Receptors

    Receptors that indirectly influence the post-synaptic cell's response through a secondary messenger system.

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    G-protein–coupled receptors

    Receptors that act as first messengers and trigger second messengers to open or close gated channels.

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    Removal of Neurotransmitters

    Neurotransmitters are removed from the synaptic cleft by enzymatic breakdown or reuptake by cells.

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    Study Notes

    Action Potential Depolarization

    • Action potentials (AP) depend on ion currents and voltage-gated channels.
    • Voltage-gated sodium (Na+) channels and voltage-gated potassium (K+) channels are involved.
    • At time=0, Na+ channels open, and Na+ flows in, depolarizing the membrane.
    • Na+ channels close and inactivate.
    • K+ channels open, and K+ flows out, restoring the membrane potential to its resting state.
    • K+ leak channels are always open.

    Action Potential Repolarization/Falling Phase

    • AP depends on ion currents and voltage-gated channels.
    • K+ channels open, and K+ flows out.
    • Na+ channels are inactivated
    • Repolarizations happens.
    • Na+/K+ pump returns RMP (resting membrane potential) concentration gradient.
    • Refractory period occurs after repolarization.

    Hodgkin–Huxley Cycle

    • AP rise phase is a positive feedback cycle.
    • Initial depolarization opens Na+ channels and increases Na+ permeability.
    • Increased Na+ flow further depolarizes the membrane.
    • Further membrane depolarization opens more Na+ channels, amplifying the signal.

    Action Potential Propagation Along an Axon

    • APs are initiated at the axon hillock.
    • APs are conducted unchanged along the axon membrane to the terminals.
    • Dendrites and cell body have a higher concentration of K+ channels, reducing backpropagation into the soma (cell body).

    Propagation of Action Potentials

    • Action potentials move along an axon as the ion flows generated in one segment depolarize the potential in the next segment.
    • Propagation can be observed in both myelinated and unmyelinated axons.

    Action Potential Conduction in Unmyelinated Axons

    • Reduced threshold at axon hillock (spike initiating zone).
    • High concentration of Na+ channels.
    • Current spreads along the membrane toward terminals initiating a new Action potential.
    • Adjacent (downstream) Na+ channels reach threshold from large depolarization (new AP).
    • The refractory period prevents further propagation.
    • Axon diameter determines conduction speed (larger = faster; up to 40m/s).

    Saltatory Conduction

    • In myelinated axons, ions can flow across the plasma membrane only at nodes where the myelin sheath is interrupted.
    • Action potentials skip rapidly from node to node.
    • Saltatory conduction allows for thousands to millions of fast-transmitting axons to be packed into a relatively small diameter.

    Action Potential Conduction in Myelinated Axons

    • Myelin (protein and lipid) insulates and prevents ion flow across the membrane.
    • Reduces current loss.
    • Concentration of Na+ and K+ at nodes allows ions to cross the membrane.
    • Axon hillock function is similar to unmyelinated neurons.
    • Similar conduction process but the current quickly spreads between nodes.
    • Higher conduction velocities (up to 100 m/s) are observed.

    Synaptic Transmission

    • Synapses are the sites where neurons communicate.
    • Pre-synaptic neuron sends neurotransmitters.
    • Post-synaptic neuron receives neurotransmitters.
    • Chemical synapses are most common, and neurotransmitters diffuse across the synaptic cleft to post-synaptic membrane receptors.
    • Ion channels open or close, creating graded potentials (PSPs).

    Neurotransmitters

    • Stored in vesicles within axon terminals of presynaptic neurons
    • Released thru exocytosis into synaptic cleft
    • Act via ligand-gated ion channels or G-protein-coupled receptors.
    • Binding leads to depolarization or hyperpolarization.

    Two Types of Synapses

    • Electrical synapses pass directly from a presynaptic cell to the postsynaptic cell (e.g., cardiac muscle, some invertebrate neurons).
    • Chemical synapses involve the release of neurotransmitters by the presynaptic cell to diffuse across the synaptic cleft and act on receptors of the postsynaptic cell, which is common in most neurons.

    Vesicles Release Neurotransmitter

    • Action potentials trigger Ca2+ influx through voltage-gated Ca2+ channels.
    • Ca2+ causes vesicles to move to the plasma membrane, fuse, and release neurotransmitter into the cleft.

    Postsynaptic Binding

    • Neurotransmitters bind to postsynaptic receptors, opening channels that lead to depolarization (excitatory) or hyperpolarization (inhibitory).
    • These signals allow for integration of multiple presynaptic inputs (up to 1,000)

    Neurotransmitters Work in Two Ways

    • Some bind directly to ligand-gated ion channels in the postsynaptic membrane.
    • Others work more slowly by acting as first messengers and binding G protein-coupled receptors in the postsynaptic membrane and subsequently triggering second messengers.

    Neurotransmitter Removal

    • Neurotransmitters are removed from the synaptic cleft either by enzymatic breakdown or uptake by the presynaptic terminal or glial cells.

    Types of Neurotransmitters

    • Acetylcholine
    • Amino acids
    • Biogenic amines
    • Neuropeptides
    • Gases

    Receptor Protein Types

    • Ionotropic binding proteins
    • Metabotropic binding proteins

    Conclusion

    • Heart 2 shows a delayed reaction to stimulation of Heart 1, implying a chemical transmission of nerve impulses.

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    Test your knowledge on the role of neurotransmitters in the nervous system, including their effects on postsynaptic cells and the mechanisms of receptor function. Explore the differences between nicotinic and metabotropic receptors, as well as the importance of calcium ions and myelin in neurotransmission. Perfect for students studying neuroscience!

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