Action Potential

Question 1

What is Action Potential?

Answer 1

it is the new potential difference created by an effective stimulation. It is an
electrochemical signal (nervous message) due to modification in the membrane permeability
to ions.

Question 2

What are the phases of action potential?

Answer 2

a- Depolarization (or hypopolarization): the stimulation causes opening of Na + channels and
massive diffusion of Na + ions to the cross section. This diffusion makes the surface negative
and the cross section positive . The potential difference increases from -70 mv to +30
mv(potential difference increases by 100 mv). Na + channels open under the effect of
stimulation and they are called voltage dependent channels.

b- Repolarization: Na + channels close while K + channels open then K + ions diffuse to the
surface . This diffusion returns the surface positive and the cross section negative and the
potential difference decreases to -70 mv

c- Hyperpolarization :K + channels need longer to close than Na + channels. More K + ions
diffuse to the surface and the cross section becomes more negative. The potential difference
decreases to -80 mv.

Question 3

What are the types of stimulation?

Define them.

Answer 3

There are 2 types of stimulation:

1) Ineffective stimulation(infraliminary):
lf the stimulation intensity is low, the number of
Na + channels that opens is low. This produces slight hypopolarization (

Question 4

What is a threshold

Answer 4

It is the minimum intensity of stimulation that creates an action potential and
below it there is no action potential.