Membrane Potential and Ion Channels
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Questions and Answers

What role does temporal summation play in neuron communication?

  • It enhances the postsynaptic potential by using successive firing of a single presynaptic neuron. (correct)
  • It refers to the integration of information from divergent pathways.
  • It cancels out excitatory signals with inhibitory signals.
  • It occurs when multiple presynaptic neurons fire simultaneously.

    • How do action potentials maintain uniformity despite varying stimuli strengths?

  • By varying the amplitude of the action potential based on stimulus strength.
  • By filtering out weak stimuli completely.
  • By altering the neurotransmitter release per action potential.
  • Through the frequency of action potentials generated. (correct)

    • What effect does long-term potentiation (LTP) have on synaptic connections?

  • It is unrelated to neuronal plasticity.
  • It decreases the strength of synaptic connections over time.
  • It leads to increased strength of a synaptic connection through repetitive stimulation. (correct)
  • It solely relies on structural changes in the neuron.

    • What is the consequence of desensitization during high-frequency action potential firing?

    <p>It may decrease neurotransmitter release.</p> Signup and view all the answers

    Which of the following best describes a convergent pathway?

    <p>Several presynaptic neurons influence a single postsynaptic neuron.</p> Signup and view all the answers

    What might happen to signal propagation if a neurotransmitter is blocked by a neurotoxin?

    <p>It could completely halt action potential generation.</p> Signup and view all the answers

    What does neuronal plasticity allow the nervous system to do?

    <p>It allows alterations in anatomy and function in response to activity patterns.</p> Signup and view all the answers

    What factors are primarily involved in determining the strength of a stimulus?

    <p>The frequency of action potentials and neurotransmitter release.</p> Signup and view all the answers

    What is the significance of myelination in nerve impulse propagation?

    <p>It prevents the loss of electrical impulses, increasing conduction speed.</p> Signup and view all the answers

    What effect does multiple sclerosis have on action potentials?

    <p>It slows down the transmission of nerve impulses.</p> Signup and view all the answers

    During saltatory conduction, where are action potentials primarily generated?

    <p>At the nodes of Ranvier.</p> Signup and view all the answers

    What is the role of the axon hillock in a neuron?

    <p>It triggers action potentials when the threshold is reached.</p> Signup and view all the answers

    How do graded potentials differ from action potentials?

    <p>Graded potentials can vary in amplitude and are localized.</p> Signup and view all the answers

    What happens during the refractory period of a neuron?

    <p>Another action potential cannot be generated regardless of the stimulus strength.</p> Signup and view all the answers

    What role do neurotransmitters play in chemical synapses?

    <p>They are stored in the axon terminals and released into the synaptic cleft.</p> Signup and view all the answers

    What general effect do neurotoxins have on neural function?

    <p>They block or disrupt the propagation of action potentials.</p> Signup and view all the answers

    In what direction does synaptic transmission typically operate?

    <p>From the pre-synaptic neuron to the post-synaptic neuron.</p> Signup and view all the answers

    What do dendritic spines primarily facilitate?

    <p>The formation of synapses with other neurons.</p> Signup and view all the answers

    What is the main function of myelination in neurons?

    <p>To increase the speed of action potential propagation</p> Signup and view all the answers

    What occurs during the absolute refractory period?

    <p>No new action potential can be initiated</p> Signup and view all the answers

    What characterizes the propagation of action potential in myelinated fibers?

    <p>Jumping from node to node increases speed</p> Signup and view all the answers

    What is the effect of tetrodotoxin on neurons?

    <p>It prevents the generation of action potentials</p> Signup and view all the answers

    What is a key difference between graded potentials and action potentials?

    <p>Action potentials are all-or-none events</p> Signup and view all the answers

    How does repolarization occur during an action potential?

    <p>Through the opening of voltage-gated potassium channels</p> Signup and view all the answers

    What is the role of Na+-K+ pumps in neurons?

    <p>They maintain the resting membrane potential</p> Signup and view all the answers

    What distinguishes the refractory periods?

    <p>Only during the relative refractory period can a new action potential be generated with a stronger stimulus</p> Signup and view all the answers

    During which phase of action potential does the membrane potential become more positive?

    <p>Depolarization</p> Signup and view all the answers

    What happens to the action potential as it travels down a non-myelinated axon?

    <p>It loses strength as it progresses</p> Signup and view all the answers

    Which of the following best describes graded potentials?

    <p>They can vary in amplitude depending on the stimulus</p> Signup and view all the answers

    What is the outcome of the opening of chemically gated ion channels in a neuron?

    <p>Change in membrane potential leading to graded potential</p> Signup and view all the answers

    Myelinated axons are more efficient due to which of the following characteristics?

    <p>Lower energy consumption during action potential propagation</p> Signup and view all the answers

    What defines the duration of the refractory period in neurons?

    <p>It varies based on the types of channels involved</p> Signup and view all the answers

    Study Notes

    Membrane Potential

    • The voltage difference across a cell membrane is called membrane potential.
    • The resting membrane potential of a neuron cell is approximately -70 mV
    • The intracellular fluid has a slight excess of anions and the extracellular fluid has a slight excess of cations.
    • The Na+-K+ pump maintains the resting membrane potential at the expense of energy.
    • The Na+-K+ pump also functions as a leaky channel, letting potassium ions pass through the membrane.

    Change of Membrane Potential

    • Nerve and muscle tissues are excitable tissues, because their membrane potential can be altered.
    • The change of membrane potential is categorized as polarization, depolarization, repolarization, and hyperpolarization.
    • Ion movement can only be mediated by channels.

    Ion Channels

    • Pores that open and close provide a passageway for ions to pass through a membrane.
    • There are leaky channels and gated channels.
    • Gated channels can be voltage-gated, chemically gated, mechanically gated, or thermally gated.

    Generation of Electrical Signals in Neuron

    • Neurons generate an electrical signal via changes in membrane potential.
    • Such changes in membrane potential are brought about by changes in ion movement.
    • Two basic types of electrical signals are graded potential and action potential.

    Graded Potential

    • It is the depolarization of membrane in a small and specialized region of the total membrane.
    • It is initiated by Na+ entry into the cell and the ions flow from the active site to the inactive site, causing a current along the membrane.
    • It is bi-directional over a short distance.
    • It functions as a short-distance signal.
    • Graded potential is a localized change in the membrane potential that is graded depending on the intensity of the stimulus.

    Action Potential

    • It is a brief, rapid, large change in membrane potential.
    • It is initiated when the membrane potentials reach threshold potential.
    • It is generated at the axon hillock and propagated throughout the entire membrane, nondecrementally.
    • It serves as a long-distance signal.
    • It has a fixed threshold and magnitude and is all-or-none.

    Conformations of voltage-gated Na+ and K+ channels

    • Channels can open or close when they are in different conformations.
    • The channels are responsible for the formation of action potential and are voltage-gated, meaning they are opened and closed by changes in membrane potential.

    Formation of Action Potential

    • Rapid fluxes of Na+ and K+ cause the action potential.
    • Opening and closing of voltage-gated Na+ channels and voltage-gated K+ channels lead to the action potential.
    • Graded potential activates the opening of Na+ channels (fast).
    • Slow closure of Na+ channel and the opening of K+ channels (slow).
    • The positive feedback of Na+ channel allows for rapid depolarization.

    Refractory Period

    • After the action potential, there is a time period when new action potential cannot be initiated.
    • Divided into the absolute refractory period and the relative refractory period.

    Myelination

    • Axons covered with myelin along the length are called myelinated fibers.
    • Myelin is a thick layer produced by oligodendrocytes in the CNS and Schwann cells in the PNS.
    • Myelin serves as an insulator and prevents leakage of current, allowing for faster transmission of action potential.
    • Nodes of Ranvier are unmyelinated gaps between myelinated segments.

    Saltatory Conduction

    • Myelinated axons conduct action potential faster than unmyelinated axons due to saltatory conduction.
    • Action potential is only produced at the nodes of Ranvier, where Na+ channels are concentrated.
    • The current moves under the myelin sheath but diminishes in amplitude.
    • Na+ entry at the node reinforces the depolarization and keeps the magnitude high enough for the next action potential.

    Propagation of nerve impulse

    • Once an action potential is initiated, no further triggering event is needed to activate the remaining segment of the fiber.
    • Conducted through contiguous conduction or saltatory conduction.
    • Contiguous conduction occurs in non-myelinated axons and the action potential spreads along every patch of membrane down the axon.
    • Once the original action potential is initiated it starts a self-perpetuating cycle where new action potentials are formed and propagated along the fiber.

    Graded potential vs action potential

    • Graded potential is a localized change in membrane potential that is graded depending on the intensity of the stimulus, whereas action potential is an all-or-none event.
    • Action potentials are triggered when the membrane potential reaches the threshold.
    • Graded potential only occurs in a small region of the membrane, whereas action potential is propagated along the entire membrane.

    Neurotoxins

    • Tetrodotoxin (TTX) is found in the pufferfish and blocks voltage-gated Na+ channels, thus preventing action potential generation.
    • TTX is extremely deadly and can cause paralysis, loss of consciousness, respiratory failure, and death.

    Multiple sclerosis

    • An autoimmune disease, multiple sclerosis, attacks the nervous system, destroying myelin sheath.
    • This slows the transmission of nerve impulse and may block the propagation of action potentials.
    • Symptoms may depend on the affected axons and there is currently no cure.

    Integration of information transfer between neurons

    • Information is transferred between neurons via synapses, either electrical or chemical.
    • It is a unidirectional process.

    Chemical Synapse

    • A specialized junction where information is transferred from one neuron to another.
    • Synaptic vesicles containing neurotransmitters are released at the axon terminal.
    • The neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron.
    • The neurotransmitter binding initiates a new action potential on the postsynaptic neuron.

    Determination of the Post-synaptic Potential

    • The combination of excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP) determines the postsynaptic potential.
    • Temporal summation is when several EPSP occur close together in time.
    • Spatial summation is when EPSP originate simultaneously from several presynaptic inputs.
    • Temporal and spatial summation can lead to action potential on the postsynaptic neuron.

    Memory

    • Memory is the storage of acquired knowledge for later recall.
    • Short-term memory lasts seconds to hours.
    • Long-term memory lasts days to years and involves the process of consolidation, transferring short-term memory into long-term memory.
    • There is not a single memory center in the brain, but many brain regions are involved, such as the cerebellum, prefrontal cortex, and hippocampus.
    • The brain involves both structural and functional changes during the consolidation process.

    Long-term potentiation

    • LTP is a form of synaptic plasticity that occurs when repetitive stimulation of a particular synapse leads to an increase in the strength of synaptic connection.
    • This happens when synaptic transmission is strengthened over time due to repetitive use.
    • This is attributed to a strengthening of synapses in the brain due to a long-term increase in the efficiency of signal transmission across synapses.
    • It is important to note that this process is not fully understood and research is ongoing to understand it better.

    What determines the strength of a stimulus?

    • The frequency of action potentials, the amount of neurotransmitter released, and the duration of release determine the strength of a stimulus.
    • The frequency of action potentials can determine the amount of neurotransmitter release.
    • Neurotransmitter release can decrease at high frequencies, leading to desensitization, a reduction in response to a stimulus.

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    Description

    Explore the concepts of membrane potential, including resting and changing states. Understand the roles of ion channels and the Na+-K+ pump in neuronal function and excitability. Test your knowledge about polarization, depolarization, and related mechanisms in nerve and muscle tissues.

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