Table of ContentsView AllTable of ContentsHow It Works?Action PotentialsStimulus StrengthExamplesHistory
Table of ContentsView All
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Table of Contents
How It Works?
Action Potentials
Stimulus Strength
Examples
History
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The all-or-none law is a principle that states that the strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of thestimulus. If a stimulus is above a certain threshold, a nerve or muscle fiber will fire.
According to the all-or-none law, there will either be a full response or no response at all for an individual neuron or muscle fiber.
How Does the All-or-None Law Work?
If a stimulus is strong enough, anaction potentialoccurs and aneuronsends information down an axon away from the cell body and toward thesynapse. Changes in cell polarization result in the signal being propagated down the length of the axon.
The action potential is always a full response. There is no such thing as a “strong” or “weak” action potential. Instead, it is an all-or-nothing process. This minimizes the possibility that information will be lost along the way.
This process is similar to the action of pressing the trigger of a gun. A very slight pressure on the trigger will not be sufficient and the gun will not fire. When adequate pressure is applied to the trigger, however, it will fire.
An Overview of the Different Parts of a Neuron
How the Signal Triggers an Action Potential
Once the cell depolarizes to the required threshold, the action potential will fire. As the all-or-nothing law states, this action is not graded—it either happens, or it doesn’t.
A stimulus might cause sodium to enter the cell, but too few ions might enter the cell. This means that the cell won’t reach the required threshold and it will not fire.
Determining Stimulus Strength
The body still needs to determine the strength or intensity of a stimulus. It’s important to know, for example, how hot a cup of coffee is as you take an initial sip, or to determine how firmly someone is shaking your hand.
To gauge stimulus intensity,the nervous systemrelies on two sources of information:
If you take a sip of your coffee and it is very hot, the sensory neurons in your mouth will respond rapidly. A very firm handshake from a co-worker might result in both rapid neural firing and a response from many sensory neurons in your hand. In both cases, the rate and number of neurons firing provide valuable information about the intensity of the original stimulus.
According to the rate law, the more intense a stimulus is, the faster the neuron will fire. In other words, a strong stimulus will cause the neuron to fire much faster than a weak one.
RecapIt is not the action potential that conveys the strength or intensity of a signal, but rather the speed and number of neurons firing simultaneously.
Recap
It is not the action potential that conveys the strength or intensity of a signal, but rather the speed and number of neurons firing simultaneously.
Examples of the All-or-None Response
Some examples of the all-or-none response can be seen in different sensory and perceptual situations. For example:
In each case, sensory information is transmitted via the action potentials that carry the signal to the brain. Once the threshold has been reached to trigger an electrical impulse, the nerve fires and transmits the sensory information. That is an example of the all-or-nothing law in action.
It is the speed and frequency that the nerve fires that provide information to thebrainabout the intensity of the stimulus. So touching a hot pan, for example, would result in the rapid firing of a nerve impulse that would result in an immediate response.
Discovery of the All-or-None Law
While the all-or-none law was initially applied to the muscles of the heart, it was later found thatneuronsand other muscles also respond to stimuli according to this principle.
Summary
The all-or-nothing law is an important principle that describes how nerve cells either fire at full strength or do not. Because of this, important information does not lose strength as it is carried to the brain, ensuring that people are able to respond to environmental stimuli.
4 SourcesVerywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Psychological Association.All-or-none law.Klein SB, Thorne BM.Biological Psychology. Worth Pub; 2007.American Psychological Association.Refractory period.Martini F, Nath JL.Anatomy & Physiology. Benjamin Cummings; 2010.
4 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Psychological Association.All-or-none law.Klein SB, Thorne BM.Biological Psychology. Worth Pub; 2007.American Psychological Association.Refractory period.Martini F, Nath JL.Anatomy & Physiology. Benjamin Cummings; 2010.
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Psychological Association.All-or-none law.Klein SB, Thorne BM.Biological Psychology. Worth Pub; 2007.American Psychological Association.Refractory period.Martini F, Nath JL.Anatomy & Physiology. Benjamin Cummings; 2010.
American Psychological Association.All-or-none law.
Klein SB, Thorne BM.Biological Psychology. Worth Pub; 2007.
American Psychological Association.Refractory period.
Martini F, Nath JL.Anatomy & Physiology. Benjamin Cummings; 2010.
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