Another principle to be discussed is the refractory period. Through definition, the refractory duration is a duration of time during which a cabinet is incapable of repeating an activity potential. In terms of action potentials, it refers to the lot of time it takes for an excitable membrane come be all set to respond come a 2nd stimulus as soon as it returns to a resting state. There space two types of refractory periods; the absolute refractory period, which corresponds to depolarization and repolarization, and the relative refractory period, which synchronizes to hyperpolarization. Moreover, the absolute refractory duration is the interval of time throughout which a 2nd action potential cannot be initiated, no matter how large a stimulus is repetitively applied. The loved one refractory period is the interval of time throughout which a 2nd action potential can be initiated, yet initiation will call for a greater stimulus than before. Refractory periods are led to by the inactivation door of the Na+ channel. When inactivated, the Na+ channel can not respond to one more stimulus until the gates are reset.

You are watching: Period of repolarization of the neuron during which it cannot respond to a second stimulus

Propagation that an action Potential

Action potentials are usually produced at one end of a neuron and also then "propogated" prefer a tide along the axon in the direction of the opposite finish of the neuron.


Title: File:Blausen 0011 ActionPotential Nerve.png; Author: BruceBlaus; Site:; License: This paper is licensed under the creative Commons Attribution 3.0 Unported license.

The image over shows how an activity potential could have started near the cabinet soma and as the propagates down the axon towards the opposite end, the membrane potential behind the moving activity potential has repolarized and returned to resting membrane potential. The axon front of the present depolarization has actually not however depolarized and also it is additionally at relaxing membrane potential. Where the activity potential is arising we find the membrane potential depolarized and the exterior of the membrane at that spot is negative charged family member to the within of the membrane at that spot. As sodium rushes in, it will depolarize the next nearby spot ~ above the axon in the direction the the action potential is propagating. The factor that the activity potential does not depolarize the ar of axon membrane behind (or in the direction the the action potential just came from) is since that ar of membrane is most most likely in refractory periods and does no depolarize.


Title: File:Action Potential.gif; Author: Laurentaylorj; Site:; License: This paper is license is granted under the an innovative Commons Attribution-Share Alike 3.0 Unported license.

The image above is a ".gif" animation and also will play just if you check out the snapshot on the internet. Together you watch this animation, you will certainly see just how an action potential travels together a "depolarization" wave.


BYU-I image: produced W15

The image above is another ".gif" animation (must be perceived on the computer and not in publish form). This computer animation shows exactly how an action potential traveling down the axon is similar to stepping ~ above one finish of a water balloon. In reality, a pressure wave in the water balloon would gain smaller as it traveled under the length, but a traveling action potential (or depolarization wave) is recreated in ~ every clues on the axon that has voltage gated sodium channels to open up at threshold. In this method the initial strength that the depolarization wave is continuous recreated.


Title: File:Propagation of activity potential along myelinated nerve fiber en.png; Author: Helixitta; Site:; /wiki/File:Propagation_of_action_potential_along_myelinated_nerve_fiber_en.png; License: This record is licensed under the an innovative Commons Attribution-Share Alike 4.0 worldwide license.

The image above shows myelin top top a peripheral nerve axon. The myelin is consisted of of individual Schwann cells. The myelin covers the axon in a way that "insulates" the axon from depolarization waves. In this way, a depolarization also will take place only at the "Nodes that Ranvier" (or areas of bare axon in between individual myelin segments). As soon as a nerve axon is organized in this method with myelin, action potential propagation deserve to travel much quicker (nearly 10 times quicker than unmyelinated axons).


BYU-I image: produced W15

The image over is one more ".gif" animation. It shows how a myelinated axon might compare to a water balloon through segmented cuffs on it. A pressure wave produced at one segment would take trip down the size of the balloon and be recreated at every "node". An alert how the positively charged sodium entering in in ~ the an initial node reasons positive dues to travel down the axon where they can attempt come depolarize every node. The stamin of the depolarization wave decreases v distance native the original an initial depolarization area (just choose the pressure wave decreases through distance from the very first segment pressed top top the water balloon).

The myelinated axon would differ native the balloon in that the original depolarization wave could reason the next node to with threshold and recreate a depolarization occasion at the 2nd node that was equal to the first. Think about these two things:

The original depolarization event can facilitate other nodes in gaining closer to threshold. Every node the reaches threshold recreates a depolarization wave that is equal to the first Depolarization occurs only on ceiling axon in between myelin segments and not along the whole axon surface

These events together make the rate at i beg your pardon and activity potential travel to be lot faster. This "jumping" of action potential depolarization events from node to node is dubbed saltatory conduction.

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Well, do we have enough information to describe the physiology behind our introduce paragraph? Let"s talk around the feeling of touch and also see if we have a deeper understanding. Think about your fingertips; there space at least 5 different species of touch receptor that allow you come feel miscellaneous textures and pressures, yet how perform they work? Touch receptors are really just an elaborate neurons, yet they exhibition the same kinds of phenomena that we just talked about. Because that example, in ~ rest, they are permeable to K+, however not sodium, for this reason the within of the membrane is an unfavorable relative come the outside. Consequently, Na+ channel proteins space in a close up door conformation during rest. In bespeak for united state to feeling touch us will need to transform the touch stimulus right into something the brain can detect; activity potentials. The real question is just how does touch cause the neuron to send an activity potential? Remember the an activity potential is resulted in by Na+ movement throughout the membrane. Thus, the mechanical activity of touch (stimulus) reasons a conformation readjust in a special group of Na+ channels. The action of touch causes them to open, as Na+ moves v those channels, the positive charge that the Na+ ion reasons the membrane to change, and also other Na+ channels (voltage regulated) respond come the membrane change by opening. This, in turn, reasons other channels to open, and the resulting action potential is sent out as one electrical existing (called an activity potential propagation) come the brain. The mind can then interpret the activity potentials as physical touch based on where the action potentials originated from. Believe it or not, every outside stimulus, even if it is taste molecules, light waves, sound waves, or mechanically touch, is converted to an action potential. Action potentials room the interactions of the body and also the mind only functions in activity potentials.

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