Membranes and Receptors - Session 3
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Questions and Answers

What is the process called when the membrane potential decreases and the cell interior becomes less negative?

  • Repolarization
  • Threshold
  • Depolarization (correct)
  • Hyperpolarization
  • During which stage does the membrane become very permeable to sodium ions, allowing them to diffuse into the cell?

  • Depolarization Stage (correct)
  • Repolarization Stage
  • Resting Stage
  • Hyperpolarization Stage
  • What happens during hyperpolarization?

  • Sodium enters the cell, causing depolarization.
  • The cell interior becomes less negative.
  • Potassium ions flood into the cell.
  • The membrane potential becomes more negative than minus 70 mV. (correct)
  • What is the term for the restoration of the normal resting membrane potential after depolarization?

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

    What initiates the depolarization of a neuron?

    <p>The influx of sodium ions. (D)</p> Signup and view all the answers

    What is the threshold in the context of membrane potentials?

    <p>The point at which the first voltage-regulated sodium channel opens. (A)</p> Signup and view all the answers

    What role does repolarization play in cellular signaling?

    <p>It returns the cell to a state ready for another action potential. (A)</p> Signup and view all the answers

    What characterizes the resting membrane potential of a cell?

    <p>It is a stable negative charge, typically around –70 mV. (C)</p> Signup and view all the answers

    What initiates neurotransmission in a neuron?

    <p>The release of a neurotransmitter from the presynaptic neuron (C)</p> Signup and view all the answers

    What type of synaptic transmission involves the receptor protein also serving as an ion channel?

    <p>Fast synaptic transmission (A)</p> Signup and view all the answers

    Which neurotransmitter is primarily associated with excitatory postsynaptic potentials (EPSP)?

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

    What type of potential is caused by excitatory synapses leading to membrane depolarization?

    <p>Excitatory postsynaptic potential (EPSP) (B)</p> Signup and view all the answers

    Which of the following ions can be involved in inhibitory postsynaptic potentials (IPSP)?

    <p>Potassium (K+) (B)</p> Signup and view all the answers

    What characterizes slow synaptic transmission compared to fast synaptic transmission?

    <p>The receptor and channel are separate proteins. (A)</p> Signup and view all the answers

    What is one of the primary factors that influence membrane potential?

    <p>Changes in ion concentration (B)</p> Signup and view all the answers

    What effect does the Na/K-ATPase pump have on the membrane potential?

    <p>Contributes to a more negative membrane potential (A)</p> Signup and view all the answers

    What effect does opening K+ or Cl- channels generally have on the membrane potential?

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

    What is the primary function of ligand-gated ion channels?

    <p>Open or close in response to the binding of a chemical ligand (B)</p> Signup and view all the answers

    What does increasing membrane permeability to Na+ ions do to the membrane potential?

    <p>Moves it towards ENa (D)</p> Signup and view all the answers

    Which statement about the Nicotinic Acetylcholine Receptors is true?

    <p>Allow both Na+ and K+ ions to pass through (C)</p> Signup and view all the answers

    What type of gating occurs when channels respond to membrane deformation?

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

    How do changes in membrane potential arise?

    <p>Due to changes in selective ionic permeability (B)</p> Signup and view all the answers

    When is an action potential generated in a neurone?

    <p>When the membrane potential reaches a particular threshold (C)</p> Signup and view all the answers

    What is typically the role of the presynaptic neurone in synaptic transmission?

    <p>Releases neurotransmitters to communicate with the postsynaptic neurone (D)</p> Signup and view all the answers

    Flashcards

    Depolarization

    The change in membrane potential where the inside of the cell becomes less negative. This happens when positively charged ions like sodium enter the cell.

    Hyperpolarization

    The change in membrane potential where the inside of the cell becomes more negative. This happens when positively charged ions like potassium leave the cell.

    Repolarization

    The return of the membrane potential to its resting state after depolarization or hyperpolarization.

    Threshold

    The point at which the first voltage-gated sodium channel opens during a change in membrane potential.

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    Action Potential

    A rapid change in membrane potential, usually caused by the sudden influx of sodium ions, making the cell more positive.

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    Refractory Period

    The period after an action potential where the neuron is less likely to fire another action potential. It helps prevent the neuron from getting overwhelmed.

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    Sensory Transduction

    The process where a sensory stimulus, such as light or sound, is converted into an electrical signal that the nervous system can understand. This is done by specialized cells called receptors.

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    Synaptic Transmission

    The electrical signal that travels across the synapse between neurons, triggering another action potential in the receiving neuron. This is done by neurotransmitters, which bind to specific receptors on the receiving neuron.

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    Neurotransmission

    The process of releasing a neurotransmitter from the presynaptic neuron, its diffusion across the synapse, binding to receptors on the postsynaptic neuron, eliciting a response, and finally being cleared or deactivated.

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    Synapse

    The junction between two neurons, or between a neuron and a target cell, where communication occurs through the release of neurotransmitters.

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    Fast synaptic transmission

    A type of synaptic transmission where the receptor protein is also an ion channel. Neurotransmitter binding directly opens the channel, allowing ions to flow across the membrane.

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    Excitatory Synapse

    A synapse where neurotransmitter binding causes the postsynaptic membrane to become more positive (depolarized), increasing the likelihood of an action potential.

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    Inhibitory Synapse

    Synapses where neurotransmitter binding causes the postsynaptic membrane to become more negative (hyperpolarized), decreasing the likelihood of an action potential.

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    Slow synaptic transmission

    A type of synaptic transmission where the receptor and ion channel are separate proteins. Neurotransmitter binding triggers a series of intracellular events that eventually lead to channel opening.

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    Changes in ion concentration's effect

    A method of influencing membrane potential where changes in the concentration of ions, especially potassium, can alter the excitability of the membrane.

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    Electrogenic pumps

    An active transport protein that pumps sodium ions out of the cell and potassium ions into the cell, contributing to the membrane potential.

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    Voltage-Gated Channels

    A type of ion channel that opens or closes in response to changes in membrane potential. They play a crucial role in generating action potentials.

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    Ligand-Gated Channels

    A type of ion channel that opens or closes in response to the binding of a specific chemical messenger, called a ligand. These channels are often found at synapses, where they help transmit signals between neurons.

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    Mechanically Gated Channels

    A type of ion channel that opens or closes in response to mechanical forces, such as stretch, pressure, or vibration. These are found in specialized sensory cells like the hair cells in the inner ear, which detect sound waves, and in the carotid sinus, which monitors blood pressure.

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    Membrane Ion Permeability

    A key factor in the generation of membrane potential, which is the difference in electrical charge across a cell membrane. The permeability of the membrane to different ions plays a crucial role in determining the resting membrane potential and how it changes.

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    Changing Membrane Ion Permeability

    The movement of ions through the membrane via channels, which can either be opened or closed. The opening and closing of ion channels is a key way of altering the membrane potential and generating electrical signals in cells.

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    Presynaptic Neuron

    A neuron that sends a signal across a synapse. When an action potential reaches the axon terminal of the presynaptic neuron, it triggers the release of neurotransmitters.

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    Postsynaptic Neuron

    A neuron that receives a signal across a synapse. The postsynaptic neuron has receptors that bind to neurotransmitters released from the presynaptic neuron, causing a change in its membrane potential.

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    Study Notes

    Membranes and Receptors - Session 3

    • Lecture 3.2: Changing Membrane Potentials
    • Changes in membrane potential are fundamental to cell signaling, both between cells and within a single cell.
    • Examples:
      • Action potentials in nerve and muscle cells
      • Triggering and controlling muscle contractions
      • Regulating hormone and neurotransmitter secretion
      • Transduction of sensory information into electrical signals
      • Postsynaptic actions in fast synaptic transmission

    Depolarization

    • A decrease in membrane potential from its normal value.
    • The cell interior becomes less negative.
    • Example: A change from −70 mV to −50 mV.
    • Occurs when sodium ions enter the cell.

    Hyperpolarization

    • An increase in the size of the membrane potential from its normal value.
    • The cell interior becomes more negative.
    • Example: A change from −70 mV to −90 mV.
    • Occurs when potassium ions leave the cell.

    Repolarization

    • The return to the resting membrane potential after depolarization or hyperpolarization.
    • Moves back towards −70 mV.

    Threshold

    • The membrane potential value that triggers the opening of voltage-gated sodium channels.
    • This is the point where the first voltage-regulated sodium channel opens.

    Positive Charge for Depolarization

    • To depolarize a cell, a positive charge must be introduced into the cell.

    Depolarization Stage

    • Membrane permeability to sodium ions suddenly increases.
    • Large numbers of positively charged sodium ions enter the axon.
    • The normal polarized state (−90 mV) is neutralized, and the potential rapidly rises in the positive direction—this is depolarization.

    Repolarization Stage

    • Within milliseconds of depolarization, sodium channels close.
    • Potassium channels open more than usual.
    • Rapid potassium ion diffusion out of the axon re-establishes the normal negative resting membrane potential—this is repolarization.

    Voltage-Gated Sodium Channels

    • Channels that open and close at specific membrane potentials.
    • These channels are crucial for action potentials.
    • Different stages:
      • Inactivated or delayed (+35 to -90 mV)
      • Resting (-90 mV)
      • Activated (-90 to +35 mV)

    Voltage-Gated Potassium Channels

    • Channels that respond to changes in membrane potential.
    • They play a role in repolarization and return to the resting state.
    • Stages:
      • Resting (-90mV)
      • Slow activation (+35 to -90mV)

    Action Potential Graph

    • Describes voltage changes over time.
    • Shows the phases of depolarization, repolarization, and refractory period.

    Changing Membrane Ion Permeability

    • Membrane permeability changes influence membrane potential changes.
    • The potential moves towards the equilibrium potential for the ion.
    • Equilibrium potentials for key ions:
      • K⁺: −95 mV
      • Na⁺: +70 mV
      • Ca²⁺: +122 mV
      • Cl⁻: −96 mV

    Less Selective Channels (Example: Nicotinic Acetylcholine Receptors)

    • Channels that aren't exclusively selective to one type of ion.
    • The nicotinic acetylcholine receptors allow both Na⁺ and K⁺ ion passage but block anions.
    • Situated at the neuromuscular junction.

    Controlling Channel Activity

    • Channels can open or close, and this is termed gating.
    • Types of Gating:
      • Ligand Gating: Channels open or close in response to chemical ligands, e.g., neurotransmitters at synapses.
      • Voltage Gating: Channels respond to changes in membrane potential; crucial for action potentials.
      • Mechanical Gating: Channels respond to membrane deformation, e.g., mechanoreceptors.

    Synaptic Transmission

    • Action potentials travel across synapses via neurotransmission.
    • Neurotransmission begins with the presynaptic neuron releasing a neurotransmitter.
    • Neurotransmitters travel across the synaptic cleft and bind to receptors on the postsynaptic membrane.
    • The postsynaptic neuron responds appropriately, and the neurotransmitter is removed or deactivated.

    Generic Neurotransmitter System

    • Illustrates the process of neurotransmitter release, binding, and subsequent degradation/removal.

    Synaptic Connections

    • Synapses occur between nerve cells, nerve-muscle cells, and nerve-gland cells.
    • At each synapse, a chemical transmitter from the presynaptic cell interacts with receptors on the postsynaptic membrane.

    Fast Synaptic Transmission

    • Receptor proteins are ion channels.
    • Transmitter binding directly opens the channel.

    Excitatory Synapses

    • Excitatory transmitters open ligand-gated channels that increase membrane permeability to Na⁺ and Ca²⁺.
    • Membrane depolarization results, creating an EPSP (excitatory postsynaptic potential).
    • Examples include glutamate and acetylcholine.

    Inhibitory Synapses

    • Inhibitory transmitters open ligand-gated channels that increase membrane permeability to K⁺ or Cl⁻.
    • Membrane hyperpolarization occurs, creating an IPSP (inhibitory postsynaptic potential).
    • Examples include GABA and glycine.

    Postsynaptic Potentials (ERP and IPSP)

    • Postsynaptic potentials resulting from excitation and inhibition.

    Slow Synaptic Transmission

    • Receptor proteins and ion channels are distinct.
    • Two basic mechanisms:
      • Direct G-protein gating
      • Gating via an intracellular messenger (e.g., receptor-G-protein channels).

    Two Other Factors Influencing Membrane Potential

    • Ion Concentration Changes: Extracellular potassium concentration is especially significant, affecting membrane excitability; alterations can occur clinically (e.g., hyperkalemia).
    • Electrogenic Pumps: Na+/K+-ATPase pumps contribute to membrane potential by moving ions across the membrane; some drugs affect this pump.

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    Description

    Explore the intricate dynamics of membranes and receptors in this quiz, which delves into key concepts like depolarization, hyperpolarization, and repolarization. Understand the importance of membrane potential changes in cell signaling, including examples from nerve and muscle cells. Test your knowledge on how these processes contribute to muscle contractions and sensory information transduction.

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