Refractory periods absolute and relative dating

Q&A : Absolute vs. Refractory period of cardiac muscle cells .

refractory periods absolute and relative dating

nerve impulse in the neuron. Compare relative refractory period. relative refractory period. From: absolute refractory period in A Dictionary of Psychology» . To: [email protected]; Subject: Relative refractory period [ HAPP-L]; From: Ken Saladin ; Date: Mon, 18 Oct 48 ) says that the absolute refractory period (ARP) lasts only until repolarization is about. Under a double pulsed excitation we study the absolute and relative refractory periods, similarly to what can be found in neural excitability, and.

refractory periods absolute and relative dating

Moreover, the absolute refractory period is the interval of time during which a second action potential cannot be initiated, no matter how large a stimulus is repeatedly applied. The relative refractory period is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before. Propagation of an Action Potential Action potentials are usually generated at one end of a neuron and then "propogated" like a wave along the axon towards the opposite end of the neuron.

Blausen ActionPotential Nerve. This file is licensed under the Creative Commons Attribution 3. The image above shows how an action potential might have started near the cell soma and as it propagates down the axon towards the opposite end, the membrane potential behind the moving action potential has repolarized and returned to resting membrane potential.

refractory periods absolute and relative dating

The axon ahead of the current depolarization has not yet depolarized and it is also at resting membrane potential. Where the action potential is occurring we find the membrane potential depolarized and the outside of the membrane at that spot is negatively charged relative to the inside of the membrane at that spot.

refractory periods absolute and relative dating

As sodium rushes in, it will depolarize the next adjacent spot on the axon in the direction that the action potential is propagating. The reason that the action potential does not depolarize the section of axon membrane behind or in the direction that the action potential just came from is because that section of membrane is most likely in refractory periods and does not depolarize.

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The image above is a ". As you watch this animation, you will see how an action potential travels as a "depolarization" wave.

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  • Refractory Period

This animation shows how an action potential traveling down the axon is similar to stepping on one end of a water balloon. In reality, a pressure wave in the water balloon would get smaller as it traveled down the length, but a traveling action potential or depolarization wave is recreated at every spot on the axon that has voltage gated sodium channels to open at threshold.

refractory periods absolute and relative dating

In this way the original strength of the depolarization wave is continually recreated. Propagation of action potential along myelinated nerve fiber en. The image above shows myelin on a peripheral nerve axon. The myelin is made up of individual Schwann cells. The myelin covers the axon in a way that "insulates" the axon from depolarization waves.

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In this way, a depolarization even will occur only at the "Nodes of Ranvier" or areas of bare axon between individual myelin segments. When a nerve axon is organized in this way with myelin, action potential propagation can travel much faster nearly 10 times faster than unmyelinated axons. It shows how a myelinated axon might compare to a water balloon with segmented cuffs on it.

refractory periods absolute and relative dating

Howerver, during the relative refractory period, the neuron can be excited if a stronger than normal stimulus is applied. The strength of the stimulus needed to excite the neuron during the relative refractory period is very high initially immediately following the end of the absolute refractory period, but decreases throughout the relative refractory period until it reaches that needed to excite a neuorn at rest i.

Recovery of neuronal excitability. During the absolute refractory period, the neuron cannot be excited to generate a second action potential no matter how intense the stimulus. This recovery period is the relative refractory period during which a stronger than normal stimulus is needed to initiate a new action potential. Threshold stimulus strength required to elicit an action potential during the relative reftractory period.

No stimulus, no matter how strong, will bring the neuron to threshold during the absolute refractory period. During the relative refractory period, the neuron can be excited with stimuli stronger than that needed to bring a resting neuron to threshold. At the end of the relative refractory period, when the neuron is back to its resting state, the stimulus strength is at the minimum level required to bring a resting neuron to threshold dashed line.

The absolute refractory period is responsible for setting the upper limit on the maximum number of action potentials that can be generated during any given time period.

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In other words, the absolute refractory period determines the maximum frequency of action potentials that can be generated at any point along the axon plasma membrane. This action potential frequency, in turn, has important physiological implications for how the nervous system can respond to high-frequency stimuli, and also for the ability of the nervous system to send high-frequency signals to effector organs when needed see Frequency Coding in the Nervous System.

One final note about the refractory period is in order. As mentioned before, the numbers reported in these lectures for various physiological processes correspond to what has been established to be the "norm" or the best-studied example of the process.