What are the differences between a graded potential and an action potential?

Question

Accepted Answer

Basis of differentiation

Graded potential

Action potential

Definition

Is a variable-strength signal that can be conveyed over small distances and could lead to an action potential if it becomes strong enough to meet the threshold value of -55mv

Is a massive depolarization that can be transferred over long distances and is the actual message sent by neurons

Trigger

May be brought about by:

External stimuli in sensory neurons
Neurotransmitters released in synapses

Are triggered by membrane depolarization to threshold

Threshold

No threshold - can occur with any stimulus

Requires threshold to be reached

Occurrence

May occur in any region of the cell plasma membrane

Occurs in regions of the cell plasma membrane where there is a high concentration of voltage-gated Na+ and K+ channels

Amplitude

Varies depending on the strength of the stimulus

Is all-or-nothing and does not vary with stimulus strength

Duration

Varies depending on the duration of the stimulus, generally ranges from a few milliseconds to seconds

Consistent duration, generally relatively short lasting from 3 to 5 milliseconds

Stimulus strength

Decreases with distance

Does not decrease with distance

Ion channels

Ion channels responsible may be:

Temperature sensitive or mechanosensitive channels 
Ligand-gated (extracellular ligands such as neurotransmitters)
Channels gated by cytoplasmic signaling molecules

Ion channels responsible are:

Voltage-gated Sodium ion (Na+)
Voltage-gated Potassium ion (K+)channels

Ions involved

Usually Na+, K+, or Cl−

Usually Na+ and K+

Refractory period

None

Has absolute and relative refractory periods

Depolarization

May be depolarizing or hyperpolarizing depending on the stimulus

Always leads to depolarization of membrane and reversal of the membrane potential

Basis of differentiation	Graded potential	Action potential
Definition	Is a variable-strength signal that can be conveyed over small distances and could lead to an action potential if it becomes strong enough to meet the threshold value of -55mv	Is a massive depolarization that can be transferred over long distances and is the actual message sent by neurons
Trigger	May be brought about by: External stimuli in sensory neurons Neurotransmitters released in synapses	Are triggered by membrane depolarization to threshold
Threshold	No threshold - can occur with any stimulus	Requires threshold to be reached
Occurrence	May occur in any region of the cell plasma membrane	Occurs in regions of the cell plasma membrane where there is a high concentration of voltage-gated Na+ and K+ channels
Amplitude	Varies depending on the strength of the stimulus	Is all-or-nothing and does not vary with stimulus strength
Duration	Varies depending on the duration of the stimulus, generally ranges from a few milliseconds to seconds	Consistent duration, generally relatively short lasting from 3 to 5 milliseconds
Stimulus strength	Decreases with distance	Does not decrease with distance
Ion channels	Ion channels responsible may be: Temperature sensitive or mechanosensitive channels Ligand-gated (extracellular ligands such as neurotransmitters) Channels gated by cytoplasmic signaling molecules	Ion channels responsible are: Voltage-gated Sodium ion (Na+) Voltage-gated Potassium ion (K+)channels
Ions involved	Usually Na+, K+, or Cl−	Usually Na+ and K+
Refractory period	None	Has absolute and relative refractory periods
Depolarization	May be depolarizing or hyperpolarizing depending on the stimulus	Always leads to depolarization of membrane and reversal of the membrane potential

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