Nervous System I: Neuronal Structure
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Questions and Answers

What are action potentials?

  • Chemical signals released at synapses
  • Information in the form of electrochemical impulses (correct)
  • Neurons with multiple dendrites
  • The central body of a neuron

    • What happens during synaptic transmission?

    The signal is transformed into a chemical signal with the release of neurotransmitter into the synaptic cleft.

    What is a soma?

    The central body of a neuron containing the nucleus.

    What type of neurons have one dendrite?

    <p>Bipolar neurons.</p> Signup and view all the answers

    What type of neurons have multiple dendrites?

    <p>Multipolar neurons.</p> Signup and view all the answers

    What are synaptic knobs?

    <p>The terminal end of an axon that forms connections with target cells.</p> Signup and view all the answers

    What is the synaptic cleft?

    <p>The small gap between neurons.</p> Signup and view all the answers

    In which direction does an action potential travel?

    <p>From the cell body to the axon.</p> Signup and view all the answers

    What is the difference between a neuron and a nerve?

    <p>A neuron is a single cell; a nerve is a large bundle of many axons from different neurons.</p> Signup and view all the answers

    What is the resting membrane potential (RMP)?

    <p>An electric potential across the plasma membrane of approx -70mV.</p> Signup and view all the answers

    What are the two primary membrane proteins necessary to establish RMP?

    <p>The Na/K ATPase and the potassium leak channels.</p> Signup and view all the answers

    What does the Na/K ATPase do?

    <p>It pumps three Na+ out of the cell and pumps 2 K+ into the cell.</p> Signup and view all the answers

    What are leak channels?

    <p>Channels that are open all the time and allow ions to leak across the membrane.</p> Signup and view all the answers

    What is the ratio of Na to K leak channels?

    <p>1:100.</p> Signup and view all the answers

    Are neurons the only cells with a resting membrane potential?

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

    What happens if potassium leak channels are blocked?

    <p>It will reduce the resting membrane potential, making the cell less negative.</p> Signup and view all the answers

    What will happen if Na is allowed to leak down its gradient?

    <p>The cell will be more positive.</p> Signup and view all the answers

    What is polarization?

    <p>Negative on the inside, positive on the outside.</p> Signup and view all the answers

    What is depolarization?

    <p>A disturbance of the membrane potential.</p> Signup and view all the answers

    What is repolarization?

    <p>Going back to resting membrane potential.</p> Signup and view all the answers

    What are the key proteins for depolarization?

    <p>Voltage-gated Na channels.</p> Signup and view all the answers

    What causes the voltage-gated channels to open?

    <p>A change of the membrane potential from -70mV to -50mV.</p> Signup and view all the answers

    What is -50mV called?

    <p>Threshold potential.</p> Signup and view all the answers

    If an action potential starts at one end of an axon, will it ever run out of energy?

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

    What happens after depolarization?

    <p>Voltage-gated Na channels become inactivated.</p> Signup and view all the answers

    What happens after voltage-gated Na channels become inactivated?

    <p>Voltage-gated K channels open slowly.</p> Signup and view all the answers

    What happens after the cell is hyperpolarized to -90mV?

    <p>The Na/K ATPase and potassium leak channels continue to function.</p> Signup and view all the answers

    Can the Na/K ATPase repolarize the cell alone?

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

    What happens if a toxin prevents voltage-gated Na channels from closing?

    <p>The cell will be very positive and the membrane will not repolarize.</p> Signup and view all the answers

    What is myelin?

    <p>An insulating sheath that wraps around axons.</p> Signup and view all the answers

    Where is myelin created?

    <p>In Schwann cells.</p> Signup and view all the answers

    What is the effect of myelin sheath on action potentials?

    <p>No ions can enter or exit a neuron where the axonal membrane is covered.</p> Signup and view all the answers

    What are the nodes of Ranvier?

    <p>Periodic gaps in the myelin sheath.</p> Signup and view all the answers

    What is the advantage of myelin sheath?

    <p>It dramatically speeds the movement of the action potential.</p> Signup and view all the answers

    Is the amount of energy consumed by Na/K ATPase more in myelinated axons?

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

    What is the equilibrium potential for Na+?

    <p>+50mV.</p> Signup and view all the answers

    What is the equilibrium potential for K+?

    <p>-90mV.</p> Signup and view all the answers

    What does it indicate if the equilibrium potential for K+ is very close to the resting membrane potential?

    <p>There are a large number of K+ leak channels.</p> Signup and view all the answers

    What is the refractory period?

    <p>The phase where the passage of one action potential makes the neuron non-responsive to further depolarization.</p> Signup and view all the answers

    What is the absolute refractory period?

    <p>A neuron will not fire another action potential regardless of the strength of stimulation.</p> Signup and view all the answers

    What happens to the voltage-gated Na channels during the absolute refractory period?

    <p>They are inactivated and cannot open.</p> Signup and view all the answers

    What is the relative refractory period?

    <p>A neuron can transmit an action potential, but a greater depolarization is required.</p> Signup and view all the answers

    Study Notes

    Action Potentials

    • Electrochemical impulses that transmit information between neurons.
    • Initiates synaptic transmission at axon terminals.

    Synaptic Transmission

    • Occurs when an action potential reaches a synapse, converting electrical signals into chemical signals.
    • Neurotransmitters are released into the synaptic cleft.

    Neuronal Structure

    • Soma: Central part containing the nucleus; involved in cell's biosynthetic activities.
    • Synaptic Knobs: Terminal ends of axons that connect with target cells.
    • Synaptic Cleft: Small gap between neurons for neurotransmitter diffusion.

    Neuron Classifications

    • Bipolar Neurons: Feature a single dendrite.
    • Multipolar Neurons: Contain multiple dendrites.

    Action Potential Direction

    • Travels from the cell body down the axon.

    Neuron vs Nerve

    • Neuron: Single nerve cell.
    • Nerve: Bundle of multiple axons from various neurons.

    Resting Membrane Potential (RMP)

    • Approximately -70mV; interior of the cell is negatively charged.
    • Maintained by two primary proteins: Na/K ATPase and potassium leak channels.

    Na/K ATPase Function

    • Pumps three Na+ ions out and two K+ ions into the cell, resulting in a net charge of -1 inside.
    • Establishes sodium and potassium gradients across the membrane.

    Ion Leak Channels

    • Always open; allow ions to passively move according to concentration gradients.
    • Primarily permits K+ to exit, influencing membrane potential.

    Effects of Ion Leak Channel Blockade

    • Blocking potassium channels reduces RMP, making the interior less negative.

    Polarization Effects

    • Polarization: Negative inside, positive outside.
    • Depolarization: Reduction in negativity or potential shift to positive.
    • Repolarization: Return to resting membrane potential.

    Key Proteins in Depolarization

    • Voltage-gated Na+ channels enable Na+ influx, leading to cell positivity.

    Threshold Potential

    • At -50mV, triggers action potential initiation.

    Action Potential Propagation

    • Once initiated, the action potential is self-propagating and maintains amplitude.

    After Depolarization Mechanism

    • Voltage-gated Na+ channels inactivate around +35mV; followed by voltage-gated K+ channels opening to repolarize the cell.

    Hyperpolarization

    • Voltage drops to -90mV post-action potential due to K+ efflux.

    Role of Na/K ATPase in Repolarization

    • While Na/K ATPase can eventually restore RMP, rapid repolarization is primarily due to voltage-gated K+ channels.

    Effects of Toxins on Voltage-Gated Channels

    • If toxins prevent Na+ channel closure, hyperpolarization persists, causing excessive cell positivity.

    Myelin Sheath

    • Insulating covering around axons created by Schwann cells.
    • Prevents ion flow in myelinated regions, enhancing signal transmission efficiency.

    Nodes of Ranvier

    • Gaps in myelin where voltage-gated channels are concentrated.
    • Facilitate saltatory conduction, speeding action potential propagation.

    Energy Consumption in Myelinated Axons

    • Energy use by Na/K ATPase is lower in myelinated axons due to restricted activity to nodes.

    Equilibrium Potentials

    • Na+ Equilibrium Potential: +50mV, inhibiting further Na+ influx.
    • K+ Equilibrium Potential: -90mV, preventing further K+ efflux.

    Refractory Periods

    • Absolute Refractory Period: No new action potential regardless of stimulus strength due to inactivated Na+ channels.
    • Relative Refractory Period: Action potential can be induced but requires a stronger stimulus due to hyperpolarization.

    Summary of Refractory Period Behavior

    • Voltage-gated Na+ channels remain inactive during the absolute refractory period, only recovering as the membrane potential normalizes.

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    Description

    This set of flashcards covers key concepts related to the neuronal structure and function within the nervous system. Topics include action potentials, synaptic transmission, and the role of the soma. Perfect for students looking to reinforce their understanding of neuroscience.

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