What is the definition of All Or None Principle?

All-or-none principle: a nerve or muscle cell's response to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential (threshold of an action potential), the nerve or muscle fiber will respond completely; otherwise, there is no response. For example, when a motor unit in the biceps brachii is stimulated it contracts the same way whether a 10 lb or 50 lb dumbbell is lifted.  It is actually the number of muscle cells and the size of the motor unit that determines force output.  

Image: By BruceBlaus - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=28761830

All Or None Principle

Related Terms

  • Action potential
  • Threshold potential
  • Motor unit
  • Neuron
  • Muscle fiber
  • Excitability


  • Threshold Law
  • All-or-none law
  • All-or-nothing law,

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