to clarify what is an action potential.

1. Action Potential
A Summary lecture for Medical student.
Designed by: “Dr Ayub Abdulcadir Scek”
Any mistake about this lecture I’m here to apologize, because we are humans.
Any ideas or suggestions contact me.
‫التوفيق‬ ‫لكم‬ ‫اتمنى‬

2. Introduction:
• All excitable tissue mainly (nerve & muscle tissue)
have membrane potential.
• Membrane potential: cell that exhibit the polar
(charged) electricity.
• Resting membrane potential or polarized cell: is a
excitable cell that have positive charge outside and
negative charge inside during resting state.
• Two factors determine the polarity of the
cell:
1. Ion Channels.
2. Electrolyte (Na, K, Ca) movement in/out of the
cell.

4. • Why inside the cell is negative
compared to the outside?
• Two main factors responsible for this and these are:
1. Slow leakage of K ions outside the cell.
2. Presence of large non diffusible substance inside
the cell and these are protein, sulfur, phosphate.

5. Different action potential graph of many cell that each
of them starts from (-) then toward (+) direction.

6. Normal resting membrane
potential:
• Nerve or skeletal muscle = - 70 or – 90 mV.
• Cardiac muscle = - 90 mV.
• Smooth muscle = - 60 mV.
• Pacemaker = - 40 mV.
• All these negativity are caused by leakage of K ions
& negative non diffusible substances inside the cell.
• (But in action potential this polarity will change).

7. • Is a sudden reversal of polarity cell by a stimuli from
negative to positive then at the end return to negative.
• The stimuli may be:
A. Electrical stimuli.
B. Chemical stimuli.
C. Mechanical stimuli.
• Importance of action potential of the cell are:
1. Transmission of impulses along nerve fibers
2. Release of neurosecretions or chemical transmitters in
synapses.
3. Contraction of muscle.
4. Activation or inhibition of glandular secretion.

9. • Phases of action potential:
A. Depolarization phase.
B. Repolarization phase.
• Another phase present in cardiac muscle and others
have additional phase called the Plateau phase.
• Also we can divide an action potential into 5 phases:
1. The resting potential.
2. Threshold.
3. The rising phase.
4. The falling phase.
5. The recovery phase.

10. Phases Of Action Potential:

11. • Definition: Is change from negative direction
toward the positive direction.
• Causes: Na enter inside the cell = (+).
• From: example – 70 mV upto + 35 mV.
• The graph will be:

12.  When Na channels opens and more Na enters
the cell, the other channels are closed.
 Now the action potential is generated.
 And inside the cell is more positive.

13. • So what will happens when action potential is
generated & reached the peak of the graph?
• The answer is perform the importance of action
potential as mentioned previously and these are:
1. Transmission of impulses along
nerve fibers.
2. Release of neurosecretions or
chemical transmitters in synapses.
3. Contraction of muscle.
4. Activation or inhibition of glandular
secretion.

14. • Definition: Is change from positive direction toward
the negative direction.
• Causes: more K exist outside the cell = (-).
• From: example +35 mV down to – 70 mV.
• The graph will be:

15.  When K channels opens and more K leaves the cell,
the other channels are closed.
 Now the cell is back to it’s origin polarity (resting
membrane potential).
 Now the actions potential is end.

16. • Definition: Is maintaining the positive charge inside
the cell.
• Causes: more Ca enter inside the cell = (+).
• From: example maintaining toward +35 mV.
• The graph will be:

17.  When Ca channels opens and more Ca enters the cell,
the other channels are closed.
 Now the cardiac muscle cell will contracted & pumps
blood to the body or lungs.

18. • We said that Na ions are inside the cell and Ca
are inside the cell and K ion are outside the cell.
• How to restore these ions back to normal level?.
• There are two pumps used for this situation and
these pumps use ATP.
1- Na – K pumps (ATPase): pumps 3 Na outside the
cell & takes 2 K inside the cell.
2- Ca pumps: pumps Ca outside the cell or to
Sarcoplasmic reticulum if it’s muscle.