Action Potential: Step-by-Step Animation
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Questions and Answers

Which of the following is NOT one of the events that occur during an action potential?

  • Reversal of the sodium-potassium pump (correct)
  • Depolarization of the membrane potential
  • Opening of voltage-gated sodium channels
  • Increase in potassium permeability
  • What is the primary function of synaptic vesicles in the presynaptic terminal?

  • To generate action potentials
  • To maintain the resting membrane potential
  • To propagate the action potential along the axon
  • To store and release neurotransmitters (correct)
  • Which of the following describes saltatory conduction?

  • Continuous propagation of the action potential along the axon
  • Propagation of the action potential through chemical synapses
  • Discontinuous propagation of the action potential, jumping from node to node (correct)
  • Propagation of the action potential through electrical synapses
  • What is the primary function of neurotransmitter receptors on the postsynaptic membrane?

    <p>To respond to neurotransmitters and generate postsynaptic potentials</p> Signup and view all the answers

    What is the primary difference between an action potential and a graded potential?

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

    During the resting membrane potential, what is the primary driver for the high concentration of K+ inside the axon?

    <p>Active transport by the Na+/K+ ATPase pumping K+ into the axon</p> Signup and view all the answers

    What is the primary driving force for the depolarization phase of the action potential?

    <p>Influx of Na+ through voltage-gated Na+ channels</p> Signup and view all the answers

    During the repolarization phase, what is the primary mechanism that restores the negative resting membrane potential?

    <p>Closure of voltage-gated Na+ channels and efflux of K+ through K+ channels</p> Signup and view all the answers

    What is the primary role of the voltage-gated Na+ channel's activation gate?

    <p>To open the channel when the membrane potential reaches the threshold, allowing Na+ influx</p> Signup and view all the answers

    What is the purpose of the voltage-gated Na+ channel's inactivation gate?

    <p>To keep the channel closed for 1-2 ms after it has closed, preventing premature reopening</p> Signup and view all the answers

    What is the primary role of the K+ leak channels during the action potential?

    <p>To establish the resting membrane potential by allowing K+ efflux</p> Signup and view all the answers

    What happens when an inhibitory receptor is activated?

    <p>Dendrite hyperpolarization</p> Signup and view all the answers

    Which type of receptor activation leads to dendrite depolarization?

    <p>Excitatory receptor</p> Signup and view all the answers

    What is the primary result of graded potentials in the dendrites and cell body?

    <p>Summation of excitatory and inhibitory inputs</p> Signup and view all the answers

    What property distinguishes graded potentials from action potentials?

    <p>Decremental nature over time and distance</p> Signup and view all the answers

    When multiple EPSPs from different sites meet at the same time and place on the membrane, what type of summation occurs?

    <p>Spatial summation</p> Signup and view all the answers

    Why might an action potential not occur even if an EPSP surpasses the threshold?

    <p>Absence of Na+ voltage-gated channels</p> Signup and view all the answers

    What makes every neuron a complex 'computer' in processing inputs?

    <p>Integration of EPSPs and IPSPs at the axon hillock</p> Signup and view all the answers

    What is the primary function of synaptotagmin and complexin in the synaptic vesicle fusion process?

    <p>To prevent premature fusion and release after zippering of v-SNAREs and t-SNAREs</p> Signup and view all the answers

    What is the role of calcium influx in the synaptic vesicle fusion process?

    <p>Calcium influx triggers the disengagement of complexin from the SNARE complex</p> Signup and view all the answers

    How do the botulinum toxins produced by Clostridium botulinum impair synaptic function?

    <p>They prevent the assembly and function of v-SNAREs and t-SNAREs, impairing vesicle fusion</p> Signup and view all the answers

    What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft?

    <p>Degradation by enzymes, such as acetylcholinesterase</p> Signup and view all the answers

    How can different neurotransmitters elicit different effects on the postsynaptic cell?

    <p>All of the above</p> Signup and view all the answers

    What is the primary mechanism of action for ionotropic neurotransmitter receptors?

    <p>They open ion channels when the neurotransmitter binds</p> Signup and view all the answers

    How do metabotropic neurotransmitter receptors typically elicit their effects on the postsynaptic cell?

    <p>They are linked to G-protein signaling pathways and second messenger systems</p> Signup and view all the answers

    What is the primary mechanism by which acetylcholine can have both excitatory and inhibitory effects on the postsynaptic cell?

    <p>Acetylcholine can bind to both nicotinic and muscarinic receptors, which have different effects</p> Signup and view all the answers

    How do the different types of botulinum toxins (Botox) produced by Clostridium botulinum differ in their medical applications?

    <p>The different types are used to treat different muscle spasticity disorders and migraines</p> Signup and view all the answers

    What is the primary difference between continuous conduction and saltatory conduction?

    <p>In continuous conduction, the action potential progresses by depolarizing each segment of the axon, while in saltatory conduction, it 'jumps' from one node of Ranvier to the next.</p> Signup and view all the answers

    What is the primary function of myelin in facilitating saltatory conduction?

    <p>Myelin provides insulation, allowing the electrical field from one node of Ranvier to 'jump' to the next.</p> Signup and view all the answers

    Which type of nerve fiber would conduct an action potential the fastest?

    <p>A-fibers, which are large, myelinated fibers.</p> Signup and view all the answers

    What is the primary mechanism by which neurotransmitters are transported to the presynaptic terminal?

    <p>Neurotransmitters are packaged into vesicles and transported via fast axonal transport along microtubules.</p> Signup and view all the answers

    What is the primary function of the proton gradient in the presynaptic terminal?

    <p>It transports neurotransmitters into the synaptic vesicles.</p> Signup and view all the answers

    Which of the following statements about the function of neurotransmitters is correct?

    <p>Neurotransmitters are released from the presynaptic terminal and bind to receptors on the postsynaptic cell membrane, affecting the postsynaptic cell in various ways.</p> Signup and view all the answers

    According to the information provided, which of the following statements about the relationship between axon diameter and conduction velocity is correct?

    <p>Conduction velocity in myelinated axons increases linearly with increasing axon diameter, while in unmyelinated axons, it increases with the square root of the diameter.</p> Signup and view all the answers

    Which of the following statements about the structure of a chemical synapse is correct?

    <p>The presynaptic terminal of the axon is the site of neurotransmitter release, and the dendritic spine expresses the receptors for the neurotransmitter.</p> Signup and view all the answers

    Study Notes

    Action Potentials and Synaptic Transmission

    Myelinated and Unmyelinated Fibers

    • Velocity of action potentials along myelinated and unmyelinated axons
    • Velocity of myelinated fiber in m/s = diameter (um) x 4.5
    • Velocity of unmyelinated fiber in m/s = square root of diameter (um)
    • Increase in conduction velocity with increased size of axon diameter (true for myelinated and unmyelinated axons)

    Saltatory Conduction

    • Fast conduction due to myelin insulation allowing electrical field to "jump" to next node of Ranvier
    • Portions covered by myelin do not experience action potentials (no ion channels and myelin keeps ions from crossing the cell membrane)

    Fiber Types

    • A Fibers: largest fibers, 5-20 μm, myelinated, conduct impulses at 12-130 m/sec or 280 miles/hr (large sensory nerves for touch, pressure, position, heat, cold, and motor system)
    • B Fibers: medium fibers, 2-3 μm, non-myelinated, conduct impulses at 15 m/sec or 32 miles/hr (from viscera to brain and spinal cord, autonomic efferents to autonomic ganglia)
    • C Fibers: smallest fibers, non-myelinated, conduct impulses at 0.5-2 m/sec or 1-4 miles/hr (pain, touch, pressure, heat, cold from skin and pain impulses from viscera, visceral efferents to heart, smooth muscle and glands)

    Chemical Synapses

    • Associated with excitable cells
    • Presynaptic neuron releases neurotransmitter (NT) that binds to receptors embedded in post-synaptic cell membrane
    • NT crosses the synaptic cleft and binds to receptors, affecting the post-synaptic cell in various ways
    • Synapse is usually between a dendritic spine or an axon terminal, with the dendritic spine expressing the receptor for the NT

    Neurotransmitter Vesicles

    • Synthesized and packaged in rER and Golgi, transported down the axon via microtubules (fast axonal transport)
    • Neurotransmitters (non-peptide) synthesized in the cytosol of the presynaptic terminal, transported into vesicles
    • Vesicles bind to actin within the presynaptic terminal cytoskeleton, transported to release sites (active zone) close to the synapse

    Basic Steps of NT Release

    1. v-SNARES and t-SNARES "zipper" together
    2. AP → depolarization → Ca+2 VGC opening → calcium influx into the presynaptic terminal
    3. Calcium binds to synaptotagmin → disengagement of complexin
    4. The synaptic vesicle fuses when complexin disengages → release of NT into the synapse
    5. The v-SNAREs and t-SNARES disengage, and the vesicle is re-used

    Clinical Relevance - Botox

    • Toxins produced by Clostridium botulinum impair the assembly and function of v-SNAREs and t-SNARES
    • Impairs fusion of vesicles with the presynaptic membrane, used therapeutically (in tiny doses) to reduce muscle spasticity, treat migraines, and decrease wrinkles

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    Description

    Explore the events of the action potential with an animated model showcasing the axon hillock, axon, and synaptic terminals. Learn about sodium voltage-gated channels (Na+ VGC) and potassium voltage-gated channels (K+ VGC) involved in terminating the action potential.

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