What is the all-or-nothing principle?

The all- or-nothing-law is related to neurons and is the idea that a neuron can only have a full response (fire an action potential) or no response to a stimulus due to its threshold.Once the resting potential of a neuron has been set up it can be stimulated to fire an action potential if enough neurotransmitters is released by a synapse (neurons can also be stimulated by specific stimuli if the neuron is connected to a receptor). This occurs when receptors at the synapse bind to their specific neurotransmitters causing small amounts of depolarization. If the depolarization reaches the threshold (around +30 mv) then voltage gated Na+ channels open causing depolarization to pass through the whole neuron, this is known as an action potential.