Action Potentials
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Questions and Answers

What is the primary mechanism by which depolarization and repolarization occur during an action potential?

  • Diffusion (correct)
  • Active transport
  • Facilitated diffusion
  • Osmosis

    • What is the maximum potential change that can occur during an action potential?

  • + 20 mV
  • + 30 mV (correct)
  • + 40 mV
  • + 50 mV

    • What is the primary mechanism by which the strength of a stimulus is coded in an action potential?

  • Increased amplitude of the action potential
  • Increased frequency of action potentials (correct)
  • Increased refractory period
  • Increased duration of the action potential

    • What is the term for the period of time during which an axon membrane is incapable of producing another action potential?

    <p>Absolute refractory period</p> Signup and view all the answers

    What is the primary mechanism by which action potentials are transmitted in an unmyelinated axon?

    <p>Cable spread of depolarization with influx of Na+</p> Signup and view all the answers

    What is the term for the type of conduction that occurs in myelinated axons, where the action potential 'jumps' from one node to the next?

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

    What is the functional connection between a neuron and another neuron or effector cell?

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

    What is the primary mechanism by which the refractory period of an axon is affected during the relative refractory period?

    <p>VG K+ channels open</p> Signup and view all the answers

    What is the primary function of VG Ca2+ channels in synaptic transmission?

    <p>To facilitate the flow of calcium ions into the bouton</p> Signup and view all the answers

    What type of synapse allows for the direct transfer of ions between adjacent cells?

    <p>Gap junction</p> Signup and view all the answers

    What is the term for the rapid fusion of synaptic vesicles with the axon membrane?

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

    What is the effect of inhibitory neurotransmitters on the postsynaptic membrane?

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

    What is the term for the depolarization of the postsynaptic membrane?

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

    What is the primary mechanism of ion flow in electrical synapses?

    <p>Gap junctions</p> Signup and view all the answers

    What is the term for the process by which an action potential travels down the length of an axon?

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

    What is the term for the proteins that aid in the fusion of synaptic vesicles?

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

    What is the primary cause of the resting membrane potential?

    <p>Negatively charged organic molecules within the cell</p> Signup and view all the answers

    What is the effect of depolarization on the membrane potential?

    <p>It becomes more positive</p> Signup and view all the answers

    What type of ion channels open in response to a change in membrane potential?

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

    What is the role of the Na+/K+ ATPase pump in maintaining the resting membrane potential?

    <p>It maintains the electrochemical gradient of Na+ and K+ ions</p> Signup and view all the answers

    What is the sequence of events during an action potential?

    <p>VG Na+ channels open, VG K+ channels open, and then the membrane potential returns to RMP</p> Signup and view all the answers

    What is the effect of hyperpolarization on the membrane potential?

    <p>It becomes more negative</p> Signup and view all the answers

    What is the role of the ion channels in the production of an action potential?

    <p>They change the membrane permeability to specific ions</p> Signup and view all the answers

    What is the primary cause of the rapid reversal in membrane potential during an action potential?

    <p>Increased permeability of Na+ ions</p> Signup and view all the answers

    Study Notes

    Action Potentials (APs)

    • APs occur via diffusion, without requiring active transport.
    • Once an AP is completed, the Na+/K+ ATPase pump extrudes Na+ and recovers K+.
    • APs are all-or-nothing, with a maximum potential change occurring when the threshold is reached.
    • The amplitude of an AP does not normally become more positive than +30 mV, due to the quick closure of VG Na+ channels and opening of VG K+ channels.
    • The duration of an AP is fixed, and only occurs for a specific period of time.

    Coding for Stimulus Intensity

    • The frequency of APs indicates the strength of the stimulus.
    • Increased frequency of APs means a stronger stimulus strength.

    Recruitment

    • Stronger stimuli can activate more axons with a higher threshold.
    • Recruitment allows for the activation of more axons with a higher threshold.

    Refractory Periods

    • The absolute refractory period is the time when the axon membrane is incapable of producing another AP.
    • The relative refractory period is the time when the VG ion channel shape alters, allowing the axon membrane to produce another AP, but requiring a stronger stimulus.

    Cable Properties of Neurons

    • The ability of a neuron to transmit charge through its cytoplasm is known as its cable properties.
    • An AP does not travel down the entire axon, instead, each AP is a stimulus to produce another AP in the next region of membrane with VG channels.

    Conduction in Unmyelinated Axon

    • The cable spread of depolarization with influx of Na+ depolarizes the adjacent region of membrane, propagating the AP.
    • Conduction occurs in one direction, with the previous region being in its refractory period.
    • Conduction rate is slow, requiring an AP to be produced at every fraction of a micrometer.

    Conduction in Myelinated Axon

    • Myelin prevents the movement of Na+ and K+ through the membrane.
    • Interruptions in myelin (Nodes of Ranvier) contain VG Na+ and K+ channels, allowing AP to occur only at these nodes.
    • Saltatory conduction (leaps) occurs, allowing for fast conduction rates.

    Synapse

    • A synapse is the functional connection between a neuron and another neuron or effector cell.
    • Synapses allow for the transmission of electrical impulses between cells.

    Electrical Activity of Axons

    • All cells maintain a resting membrane potential (RMP) due to the negatively charged organic molecules within the cell and limited diffusion of positively charged inorganic ions.
    • Excitability/irritability is the ability to produce and conduct electrical impulses.
    • Increase in membrane permeability can be measured by placing 2 electrodes (1 inside and 1 outside the cell).
    • Depolarization reduces the potential difference, making it more positive, while repolarization returns the membrane to its resting membrane potential.

    Ion Gating in Axons

    • Changes in membrane potential are caused by ion flow through ion channels.
    • Voltage-gated (VG) channels open in response to changes in membrane potential.
    • Gated channels are part of proteins that comprise the channel, and can be open or closed in response to changes.
    • There are 2 types of channels for K+: 1 always open, and 1 closed in resting cells.
    • The channel for Na+ is always closed in resting cells, with some Na+ leaking into the cells.

    Action Potentials (APs)

    • A stimulus causes depolarization to threshold, opening VG Na+ channels and allowing for an inward electrochemical gradient.
    • The rapid reversal in membrane potential from –70 to +30 mV occurs due to the VG Na+ channels becoming inactivated.
    • VG K+ channels open, allowing for an outward electrochemical gradient, and restoring the original RMP.

    Membrane Permeabilites

    • AP is produced by an increase in Na+ permeability, followed by an increase in K+ permeability.
    • Transmission occurs in one direction only, from the axon of the first (presynaptic) neuron to the second (postsynaptic) neuron.

    Synaptic Transmission

    • Synaptic transmission occurs through a chemical gated channel.
    • The presynaptic terminal (bouton) releases a neurotransmitter (NT), which is released from synaptic vesicles.
    • The amount of NTs released depends on the frequency of AP.
    • NT release is rapid due to the many vesicles forming fusion-complexes at the “docking site.”

    Chemical Synapse

    • The terminal bouton is separated from the postsynaptic cell by a synaptic cleft.
    • NTs are released from synaptic vesicles and diffuse across the synaptic cleft.
    • NTs bind to specific receptor proteins in the postsynaptic cell membrane, opening chemically-regulated gated ion channels.
    • EPSP (excitatory postsynaptic potential) is a depolarization, while IPSP (inhibitory postsynaptic potential) is a hyperpolarization.
    • Neurotransmitter inactivation ends transmission.

    EXITATORY AND INHIBITORY NEUROTRANSMITTERS

    • Inhibitory neurotransmitters produce a depolarization of the postsynaptic membrane called the inhibitory postsynaptic potential (IPSP), reducing the chances of a new impulse.

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    Description

    This quiz covers the process of depolarization and repolarization in action potentials, including the role of Na+/K+ ATPase pumps and voltage-gated ion channels.

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