Neurophysiology Quiz: Action Potential Phases
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Questions and Answers

What is the approximate duration of the synaptic delay?

  • 2 - 3 millisecond
  • 1 - 2 millisecond
  • 0.1 - 0.2 millisecond
  • 0.5 - 1 millisecond (correct)
  • What happens when excitatory input exceeds inhibitory input but the membrane is not sufficiently depolarized?

  • The membrane is facilitated, making it more likely to have an action potential. (correct)
  • The post-synaptic neuron reaches threshold and has an action potential.
  • The post-synaptic neuron is driven further from threshold.
  • There is no effect on the post-synaptic neuron.
  • What is the function of neuromodulators?

  • To enhance the synaptic delay.
  • To directly transmit signals across synapses.
  • To alter the effectiveness of ongoing synaptic activity. (correct)
  • To inhibit the release of neurotransmitters.
  • What is the term for the sum of activities in all pre-synaptic nuclei?

    <p>Grand post-synaptic potential</p> Signup and view all the answers

    What happens when there is a balance of activated excitatory and inhibitory inputs?

    <p>The effects of the inputs negate each other, and the post-synaptic neuron is unaffected.</p> Signup and view all the answers

    Study Notes

    Neurons and Action Potential

    • Neurons are the basic functional unit of the central nervous system.
    • Action potential is composed of four principal phases: polarization, depolarization, hyperpolarization, and repolarization.
    • The refractory period ensures unidirectional propagation of the action potential and limits the frequency of action potential.

    Refractory Period

    • The refractory period consists of two phases: absolute refractory period and relative refractory period.
    • During the absolute refractory period, the axonal membrane cannot initiate another action potential, regardless of stimulation.
    • During the relative refractory period, a second action potential can be produced only by a stronger-than-usual stimulus.
    • The length of the refractory period varies for different types of neurons.
    • A longer refractory period results in a greater delay period before a new action potential can be initiated and a lower frequency of response to repeated stimulation.

    Action Potential and Synapses

    • Action potential occurs in an all-or-none fashion.
    • A stronger stimulus triggers a greater number of action potentials per second.
    • The junction between two neurons is called the synapse.
    • A neurotransmitter carries the signal across a synapse.
    • Some synapses excite the post-synaptic neurons, while others inhibit.
    • The synaptic delay is approximately 0.5-1 millisecond.

    Neurotransmitters and Synaptic Activity

    • Neurotransmitters are quickly removed from the synaptic cleft to wipe the post-synaptic slate clean.
    • The grand post-synaptic potential depends on the sum of activities in all pre-synaptic neurons.
    • There are four possible outcomes of the grand post-synaptic potential:
      • Excitation and action potential
      • Facilitation and increased likelihood of action potential
      • Inhibition and prevention of action potential
      • No effect due to balance of excitatory and inhibitory inputs

    Neuromodulators

    • Neuromodulators are chemical messengers that bind to neuronal receptors at non-synaptic sites.
    • They activate second messenger systems that produce long-term intracellular biochemical effects, altering the effectiveness of ongoing synaptic activity.
    • Neuromodulators may act at pre-synaptic or post-synaptic sites.
    • They can fine-tune synaptic responses by influencing neurotransmitter synthesis or post-synaptic receptor sensitivity.

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    Description

    Test your knowledge of the phases of an action potential, including polarization, depolarization, hyperpolarization, and repolarization. Learn about the refractory period and its role in neural transmission.

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