Action Potential
Definition:
Active response of an excitable cell caused by an
electrical stimulus with a sufficent intensity able to
trigger a quick variation of the membrane potential.
The action potential take place into the “axonic
monticolo” (trigger point). Axonic
Monticulo
What is the “Membrane Potential”?
The membrane Potential is the difference in electrical
charge between the inside and the outside of a cell.
The membrane potential has a negative value in all the
organism cells and it is measured in mV.
This value changes depending to the different cell
types.
• Neuron cells = -70mV
• Muscolar cells = -90mV
• Red blood cells = -10mV
The negativity of the membrane potential is due to the
different concentration of the ions charge.
The specific value of the membrane potential at the
resting state depends on two factors:
• Unequal distribution of the ions on the two sides of
the membrane
• Different permeability of the membrane to different ions.
Types of Potential - Graded Potential Vs Action Potential:
An excitable cell can produce two types of potential: graded potential and action potential.
Graded Potential:
The main characteristic of the graded potential is about the amplitude, it is directly proportional to the
current intensity that generates it.
If the current intensity stays under a specific potential value, then the result is a graded potential.
Action Potential:
The main action potential properties are:
• Treshold:
It is a specific value of the membrane potential where, once reached, the action potential starts.
When this activation value is reached a sufficent number of voltage dependent Sodium (Na+)
canals opens substaining a positive feedback process called Hodgkin Cycle.
This cycle is an auto regenrating process where the positive current that goes in (thanks to the
Sodium ions) opens others depolarizing Sodium channels causing an amplification of the
positive current that goes in.
• All or Nothing Law:
An action potential in order to start must reach the treshold value. If this doesn’t happens, the
action potential doesn’t starts.
• Refractoriness:
It is the amount of time where the membrane of an excitable cell doesn’t respond to an electric
stimulus after that an action potential occurred.
It is possible to distinguish 2 types of refractoriness:
‣ Absolute:
Definition:
Active response of an excitable cell caused by an
electrical stimulus with a sufficent intensity able to
trigger a quick variation of the membrane potential.
The action potential take place into the “axonic
monticolo” (trigger point). Axonic
Monticulo
What is the “Membrane Potential”?
The membrane Potential is the difference in electrical
charge between the inside and the outside of a cell.
The membrane potential has a negative value in all the
organism cells and it is measured in mV.
This value changes depending to the different cell
types.
• Neuron cells = -70mV
• Muscolar cells = -90mV
• Red blood cells = -10mV
The negativity of the membrane potential is due to the
different concentration of the ions charge.
The specific value of the membrane potential at the
resting state depends on two factors:
• Unequal distribution of the ions on the two sides of
the membrane
• Different permeability of the membrane to different ions.
Types of Potential - Graded Potential Vs Action Potential:
An excitable cell can produce two types of potential: graded potential and action potential.
Graded Potential:
The main characteristic of the graded potential is about the amplitude, it is directly proportional to the
current intensity that generates it.
If the current intensity stays under a specific potential value, then the result is a graded potential.
Action Potential:
The main action potential properties are:
• Treshold:
It is a specific value of the membrane potential where, once reached, the action potential starts.
When this activation value is reached a sufficent number of voltage dependent Sodium (Na+)
canals opens substaining a positive feedback process called Hodgkin Cycle.
This cycle is an auto regenrating process where the positive current that goes in (thanks to the
Sodium ions) opens others depolarizing Sodium channels causing an amplification of the
positive current that goes in.
• All or Nothing Law:
An action potential in order to start must reach the treshold value. If this doesn’t happens, the
action potential doesn’t starts.
• Refractoriness:
It is the amount of time where the membrane of an excitable cell doesn’t respond to an electric
stimulus after that an action potential occurred.
It is possible to distinguish 2 types of refractoriness:
‣ Absolute:
