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Action potential patterns

Created by Matthew Barry Jensen.

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  • leafers tree style avatar for user Roger Gerard
    Is the trigger zone mentioned in so many of these videos a synonym for the axon hillock?
    (8 votes)
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  • aqualine ultimate style avatar for user Kayla Judith
    At he starts talking about the third, more complex types of neurons. If the first type is like motor neurons, and the second type is like pacemaker neurons. What is an example of this third type of neuron?
    (6 votes)
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  • female robot grace style avatar for user Nik Ami
    Hello, I want to know how an external stimuli decides whether to generate a graded potential or action potential at dendrite or in soma or at trigger zone? Thank you.
    (2 votes)
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    • spunky sam blue style avatar for user Zerglingk9012
      All external stimuli produce a graded potential. External stimuli will usually be inputted through a dendrite. The potential charge of the membrane then diffuses through the remaining membrane (including the dendrite) of the neuron. When that potential change reaches the trigger zone of the axon, if it is still over threshold, then it will open the voltage gated channels at the trigger zone causing an action potential to be fired. Additionally, multiple stimuli can add up to threshold at the trigger zone, it does not need to be one stimulus that causes the action potential.

      Simply put, all external stimuli make graded potentials. Some, but not all, graded potentials cause an action potential at the trigger zone.
      (7 votes)
  • aqualine ultimate style avatar for user Kent Green
    So he specifically mentioned the motor neurons as the ones that are silent until they have sufficient excitation; and then they fire frequently until the excitation goes away.

    The "pacemaker" neurons, might have something to do with autonomic brain and body rhythms; like the circadian rhythms for sleep / wakefulness, breathing, heart-rate... and perhaps examples of types of input that might be excitatory to some of those functions could be like the rush of adrenaline caused by fight / or flight response; or conversely relaxation would be inhibitory?

    To me, the last type described sounds like it'd be the closest pattern of those listed to what we'd associate with conscious thought, complex reasoning, etc.
    (3 votes)
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  • leafers ultimate style avatar for user Ankou  Kills
    Hi, which one of these do neurons of the digestive tract identify with?
    (1 vote)
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  • blobby green style avatar for user Alex McWilliams
    Are you able to tell me about how an axon may be brought to threshold potential through only the influence of extracellular fluid? For example, placing a negative electrode on a sensory neuron causes the neuron's axon to fire an electron potential without influencing that neuron's soma.
    (1 vote)
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  • blobby green style avatar for user rexus3388
    how is the "spontaneous action potential" affected by the resting potential?
    (1 vote)
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  • female robot ada style avatar for user Danielle Jettoo
    Im wondering how these graded potentials are measured and were discovered if, for any change to occur in the body, a full-fledged action potential must occur... thanks.
    (1 vote)
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  • duskpin sapling style avatar for user jaz.sloan
    Is the axon hillock the same in function/location as the Axon Initial Segment?
    (1 vote)
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  • blobby green style avatar for user alexbutterfield2016
    Hi there
    Im a MBBS and had a questions from our physiology which i liked to had an answer for
    Before the "After Hyperpolarization" theres a period known as "After Depolarization" ... Any ideas about the mechanism?
    (1 vote)
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Video transcript

In this video, I want to talk about action potential patterns. The information from inputs to a neuron is converted to the size, duration, and direction of graded membrane potentials in the dendrites and the soma, so that a small excitatory input to a dendrite, say, usually causes a small excitatory graded potential, also called a depolarization. And a larger excitatory input usually causes a larger excitatory potential. And the same goes for inhibitory inputs. A small inhibitory input usually causes a small hyperpolarization or inhibitory potential. And a larger inhibitory input usually causes a larger hyperpolarization or inhibitory potential. Neurons process that information by summation of the graded potentials at the trigger zone to determine if an action potential will be fired down the axon. Action potentials, however, are consistently the same size and duration for any given neuron, so that the information contained in the graded potentials is, instead, converted into a temporal pattern or a timing of action potentials being fired down the axon. So here I've drawn some lines to just represent time. And we'll look at the temporal patterns or the timing of action potentials that can happen to transmit different kinds of information down the axons of different types of neurons. Some neurons fire no action potentials until there is sufficient excitatory inputs. And then the size and duration of depolarization over threshold is converted into the frequency and duration of a series, which is also called a train of action potentials. So let's say this is one of these neurons that doesn't fire any action potentials at rest. But then if it gets sufficient excitatory input to depolarize the trigger zone over threshold right here, then we see a little train of action potentials. And I'll just write out one little line here that's often called a spike to represent one action potential. And then this neuron will fire a little train, a little series of action potentials for as long as that depolarization is over the threshold potential. And then when the depolarization ends or when it dips below the threshold at the trigger zone, the train of action potential stops, and then the neuron is quiet again. It's not firing any action potentials. So this is a very common method used by lots of neurons in the nervous system. For example, the motor neurons that synapse on skeletal muscle, they tend to fire very few or no action potentials until they're excited enough. And then they'll fire a train of action potentials, and then they're quiet again. Other neurons, however, actually fire action potentials at a regular rate in the absence of any input. And the reason they do this is that they have differences in their leak channels and/or their voltage-gated channels that actually spontaneously depolarize the membrane to threshold at a regular interval, which is very similar to how the pacemaker cells in the heart function. And with these types of neurons, excitatory input will cause them to fire action potentials more frequently during the period of time that they're excited. And then when that excitation goes away, they go back to their regular rate of firing. And inhibitory input will have the opposite effect. That will slow down their firing during the period of inhibition. And then when that goes away, they go back to their regular rate of firing again. And there are even more complicated neurons that, in the absence of input, fire little bursts of action potentials, followed by a little space. And then they have another regular little burst of action potentials. With these types of neurons, excitatory input can cause the little bursts to happen more frequently. It can cause changes within the burst, and it can cause changes to the spacing between the bursts. But then when the input goes away, they go back to their regular bursts. And the opposite happens with inhibitory input. That can slow down the frequency of these bursts. The advantage of these sorts of systems, where the neurons fire at regular rates spontaneously or in bursts, is that information passed along to the target cells can be fine-tuned in either direction, because with a neuron like this that's quiet at rest, the information can only go in one direction. It can only go from no action potentials being fired to trains of action potentials of different frequencies and durations. But if there's more inhibitory input to these types of neurons, that information can't be passed along. But with these types of neurons, information from both excitatory and inhibitory inputs can be passed along in a more fine-grained fashion. The different temporal patterns of action potentials are then converted to the amounts and temporal patterns of neurotransmitter release at the synapse. And target cells can be set up a lot of different ways to respond to these temporal patterns and amounts of neurotransmitter release.