Electrical Signals in the Nervous System
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Electrical Signals in the Nervous System

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Questions and Answers

What is the primary function of connexons in electrical synapses?

  • They release neurotransmitters.
  • They connect cells to allow graded current flow. (correct)
  • They modulate receptor activity.
  • They control ion channel opening.

    • What role does calcium (Ca2+) play in neurotransmitter release at chemical synapses?

  • It promotes the binding of neurotransmitters to receptors.
  • It causes vesicles to be absorbed.
  • It degrades neurotransmitters after release.
  • It triggers the release of neurotransmitters from vesicles. (correct)

    • What type of conduction occurs when action potentials are generated at successive nodes of Ranvier in myelinated axons?

  • Passive conduction
  • Continuous conduction
  • Reverse conduction
  • Saltatory conduction (correct)

    • Which statement about neurotransmitter receptors is true?

    <p>A neurotransmitter can only fit in one type of receptor.</p> Signup and view all the answers

    Which factor affects the speed of conduction in myelinated axons?

    <p>Thickness of the myelin sheath</p> Signup and view all the answers

    Which neurotransmitter is primarily associated with the modulation of its own release?

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

    What mechanism is responsible for the removal of acetylcholine (ACh) from the synapse?

    <p>Enzymatic degradation by acetylcholinesterase</p> Signup and view all the answers

    Which type of nerve fiber is characterized by being small-diameter and unmyelinated?

    <p>Type C</p> Signup and view all the answers

    Which of the following is NOT classified as a biogenic amine neurotransmitter?

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

    Why can action potentials only propagate in one direction along an axon?

    <p>Due to refractory period of the initial site</p> Signup and view all the answers

    What is the conduction speed of Type A nerve fibers?

    <p>15 to 120 m/s</p> Signup and view all the answers

    Which chemical class of neurotransmitters includes adenosine?

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

    In which type of muscle are electrical synapses most commonly found?

    <p>Cardiac muscle</p> Signup and view all the answers

    What role do local currents play in saltatory conduction?

    <p>They cause depolarization at the next node</p> Signup and view all the answers

    What is a key characteristic of Type B nerve fibers?

    <p>Medium-diameter and lightly myelinated</p> Signup and view all the answers

    What occurs during the repolarization phase of an action potential?

    <p>K+ movement out of the cell increases</p> Signup and view all the answers

    Which of the following statements is incorrect regarding action potentials?

    <p>They can exceed maximal stimulus frequency.</p> Signup and view all the answers

    During which phase is the neuron completely insensitive to further stimulation?

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

    What defines a threshold stimulus?

    <p>It produces a graded potential sufficient to initiate an action potential</p> Signup and view all the answers

    What is the function of voltage-gated K+ channels at the end of repolarization?

    <p>To reestablish resting membrane potential</p> Signup and view all the answers

    What is referred to as the afterpotential?

    <p>The brief period of hyperpolarization following repolarization</p> Signup and view all the answers

    What type of stimulus would be categorized as a supramaximal stimulus?

    <p>Any stimulus stronger than the maximal stimulus</p> Signup and view all the answers

    What happens to Na+ channels just after the end of the repolarization phase?

    <p>They transition to a resting state</p> Signup and view all the answers

    Which of the following accurately describes a subthreshold stimulus?

    <p>It does not result in a graded potential that can trigger an action potential</p> Signup and view all the answers

    What occurs during an excitatory postsynaptic potential (EPSP)?

    <p>Depolarization that may trigger an action potential.</p> Signup and view all the answers

    Which statement accurately describes inhibitory postsynaptic potential (IPSP)?

    <p>It hyperpolarizes the postsynaptic membrane, decreasing action potential likelihood.</p> Signup and view all the answers

    What is the effect of presynaptic inhibition?

    <p>It reduces neurotransmitter release from the presynaptic terminal.</p> Signup and view all the answers

    In spatial summation, what happens when action potentials occur at different dendrites?

    <p>They combine to exceed the threshold and produce an action potential.</p> Signup and view all the answers

    Which of the following is a characteristic of temporal summation?

    <p>It requires the action potentials to arrive in close succession.</p> Signup and view all the answers

    What role do neuromodulators play in neurotransmission?

    <p>They influence the likelihood of an action potential in the postsynaptic cell.</p> Signup and view all the answers

    Which of the following gases is classified as a neuromodulator?

    <p>Nitric oxide</p> Signup and view all the answers

    What happens during presynaptic facilitation?

    <p>It enhances the amount of neurotransmitter released.</p> Signup and view all the answers

    What produces action potentials in the nervous system?

    <p>Electrical signals generated by cells</p> Signup and view all the answers

    What primarily establishes the resting membrane potential?

    <p>Differences in ion concentrations and permeability</p> Signup and view all the answers

    Why does K+ diffuse from inside to outside the cell?

    <p>Many leak channels make the membrane more permeable to K+</p> Signup and view all the answers

    What is the typical resting membrane potential value?

    <p>−70 to −90 mV</p> Signup and view all the answers

    What prevents negatively charged proteins from moving across the membrane?

    <p>Size and charge of the proteins</p> Signup and view all the answers

    What role do Na+/K+ pumps play in membrane potential?

    <p>They maintain an unequal distribution of ions across the membrane</p> Signup and view all the answers

    What happens when gated ion channels open?

    <p>Membrane permeability changes for specific ions</p> Signup and view all the answers

    How does the accumulation of positive charges outside the membrane affect the cell's interior?

    <p>It makes the inside of the cell more negative</p> Signup and view all the answers

    Study Notes

    Electrical Signals in the Nervous System

    • Cells produce electrical signals called action potentials, which are responsible for transmitting information from one part of the body to another.
    • The membrane potential is a result of ionic concentration differences across the plasma membrane and the permeability of the membrane.
    • The Na+/K+ pump and membrane permeability are responsible for the ion concentrations across the membrane.
    • The inside of a cell has a high concentration of K+ and proteins, while the outside of a cell has a high concentration of Na+ and Cl-.
    • The resting membrane potential is the electrical potential difference across the plasma membrane of a neuron when it is not transmitting signals.
    • The resting membrane potential exists in an unstimulated (resting) cell due to the permeability characteristics of the membrane and differences in ion concentrations on each side of the membrane.
    • The membrane is more permeable to K+ due to leak channels, resulting in a higher concentration of K+ outside the cell, creating a negative charge inside the cell.
    • The voltage-gated Na+ channels activate at threshold potential, allowing Na+ to move into the cell, causing depolarization.
    • The voltage-gated Na+ channels close and K+ channels open during repolarization, causing K+ to move out of the cell, making the inside of the cell more negative, restoring the resting membrane potential.
    • The refractory period refers to the time when a neuron is less sensitive to further stimulation after an action potential.
    • Absolute Refractory Period: Neuron is completely insensitive to another stimulus.
    • Relative Refractory Period: A stronger-than-threshold stimulus can initiate another action potential.
    • The number of action potentials produced per unit of time is called action potential frequency.
    • A subthreshold stimulus does not cause an action potential, while a threshold stimulus does.
    • Maximal Stimulus: Produces the highest frequency of action potentials.
    • Submaximal Stimulus: Stimuli between the threshold and maximal stimulus.
    • Supramaximal Stimulus: Stimuli stronger than the maximal stimulus, but they cannot produce a greater frequency of action potentials.
    • Action potentials propagate down an axon in a one-way direction due to the refractory period.
    • Continuous Conduction: Action potential in one site triggers the next site.
    • Saltatory conduction: Action potentials jump from node to node in myelinated axons.
    • Myelinated axons conduct action potentials faster than unmyelinated axons.
    • Myelinated axons have thicker myelin sheaths, which increases the conduction speed.
    • Larger-diameter axons conduct action potentials faster than smaller-diameter axons because they have a greater surface area and more voltage-gated Na+ channels.
    • Type A fibers: Large-diameter, myelinated, conduct at 15-120 m/s.
    • Type B fibers: Medium-diameter, lightly myelinated, conduct at 3-15 m/s.
    • Type C fibers: Small-diameter, unmyelinated, conduct at 2 m/s or less.

    The Synapse

    • A synapse is a junction between two cells where action potentials in one cell cause action potentials in another.
    • Presynaptic Cell: Transmits signals toward the synapse.
    • Postsynaptic Cell: Target cell receiving the signal.
    • Electrical Synapse: Cells connected by gap junctions allowing graded current to flow between adjacent cells.
    • Chemical Synapse: Uses neurotransmitters to transmit information between neurons.
    • Chemical synapses have three main components: a presynaptic terminal, a synaptic cleft, and a postsynaptic membrane.
    • Neurotransmitters are released from synaptic vesicles in the presynaptic terminal by action potentials.
    • Neurotransmitters bind to receptors on the postsynaptic membrane, leading to the opening of ligand-gated ion channels.

    Receptor Molecules in Synapses

    • Neurotransmitters bind to specific receptors, only influencing cells with receptors for that neurotransmitter.
    • Certain neurotransmitters can be excitatory in some cells and inhibitory in others.
    • Neurotransmitters can also attach to presynaptic terminals and modulate their own release.

    Neurotransmitter Removal

    • Neurotransmitters are removed from the synapse by different mechanisms:
      • Acetylcholine (ACh): Acetylcholinesterase breaks down ACh into acetic acid and choline, which is recycled in the presynaptic neuron.
      • Norepinephrine: Recycled in the presynaptic neuron or diffuses away from the synapse.
      • Monoamine oxidase (MAO): Enzyme that breaks down norepinephrine.
      • Absorbed into circulation: Broken down in the liver.

    Neurotransmitters and Neuromodulators

    • Chemical messengers secreted by neurons, with some neurons secreting more than one type.
    • Major chemical classes of neurotransmitters:
      • Acetylcholine (ACh): Best understood; composed of acetic acid and choline.
      • Biogenic amines: Catecholamines and indoleamines.
      • Amino acids: Examples include glycine and glutamate.
      • Purines: Nitrogen-containing compounds derived from nucleic acids; examples include adenosine and ATP.
      • Neuropeptides: Short chains of amino acids.
      • Gases and Lipids: Examples include nitric oxide (gas), carbon monoxide (gas), and endocannabanoids (lipid-derived).

    Responses at the Postsynaptic Cells: Excitatory and Inhibitory Postsynaptic Potentials

    • Excitatory postsynaptic potential (EPSP): Depolarization occurs, which is a stimulatory response that might reach threshold, producing an action potential and a cellular response.
    • Inhibitory postsynaptic potential (IPSP): Hyperpolarization occurs, which is an inhibitory response, decreasing the likelihood of an action potential by moving the membrane potential further away from the threshold.

    Neuromodulation

    • Neuromodulators: Influence the likelihood of an action potential being produced in the postsynaptic cell.
    • Axoaxonic synapses: The axon of one neuron synapses with the presynaptic terminal (axon) of another neuron. This is common in the central nervous system.
    • Presynaptic inhibition: Reduces the amount of neurotransmitter released from the presynaptic terminal.
    • Presynaptic facilitation: Increases the amount of neurotransmitter released from the presynaptic terminal.

    Spatial and Temporal Summation

    • A single postsynaptic potential is often not enough to reach threshold.
    • Spatial summation: Two or more presynaptic neurons stimulate a postsynaptic neuron simultaneously, their graded potentials summate at the trigger zone to produce a graded potential that exceeds threshold, generating an action potential.
    • Temporal summation: Two or more action potentials arrive at the presynaptic membrane in close succession, their graded potentials summate at the trigger zone to reach threshold and produce an action potential.

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    Description

    Explore the fundamentals of electrical signals within the nervous system in this quiz. Learn about action potentials, membrane potentials, and the role of ion concentrations and permeability. Test your understanding of how these electrical signals contribute to neural communication.

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