IB BIOLOGY HL UNDERSTANDING 6.5.4 Resting potential & action potential

1. Resting potential

2. Resting potential Graded potential Active potential

3. • Membrane potential of a resting neuron.
• State of neuron at rest which is not sending
signals.
• Volts : -60 - -80 mV
• -ve sign means that inside of a neuron has –ve
charge to the outside.

4. Formation of resting potential
• Involve changing of the charge of plasma
membrane of nerve cell.
• Resting potential is driven by changing of
chemical potential energy to electrical
potential energy.

5. • Importance of substance involve in this
process are :
* potassium ion
* sodium ion
• Each of the ion has concentration gradient
within the plasma membrane of the cell.

7. • Concentration gradient of potassium and
sodium within the plasma membrane
represent the chemical form of potential
energy.
• During formation of resting potential,
chemical energy is convert into electrical
energy.

8. • This conversion involves sodium - potassium
pumps to be used.
• Sodium – potassium pumps generates and
maintain the ionic gradient of Na+ and K+ into
the cell.
• ATP also is used to transport Na+ and K+ in
opposite direction.

9. Step by step
protein pore is formed by clusters of specialized
protein that span the membrane. it is also
carried out selective permeability (specific ion
can bind to).
1

10. • Ions diffuse through ion channel.
• Each ion carry the units of electrical charge.
• Diffusion of ions will result net movement of
positive or negative charge.
• Produce voltage across membrane.
2

11. • During resting potential, a lot of potassium
channels open and few sodium channel open.
• Diffusion of K+ occurred
• From inside to outside of the cell.
• [K+ inside] higher than [K+ outside].
3
4

12. • [Cl-] will present inside of the cell.
• Cl- cannot diffuse out of the cell because there
are very few Cl- channels open.
• Leaving high negative charge inside the cell
thus build up -ve charge inside membrane.
5

13. • The separation of charge cause voltage to be
produced.
• This in turn cause the electrical gradient to
counterbalance the [K+].
6

14. Limitation of diffusion of [K+]
1. The building up of negative charge inside the
cell indefinitely is prevented by excess of
negative charge.
2. Excess negative charge exerts attractive force
that oppose the flow of additional positively
charge K+ out of the cell.

15. Graded potential

16. • Intermediate potential before action potential
take place.
• Involves ion channels which are potassium
and sodium gated channels.
• Gated channels can open and closed in
response to one of three kinds of stimuli.

17. Gated
channel
Stretch – gated ion
channels
Voltage – gated
ion channels
Ligand – gated
ion channels
• Sense stretch cells
• Open when membrane is
mechanically deformed.
• Found at synapses.
• Open and closed
when a specific
chemical
(neurotransmitter)
binds to the channel.
• Found in axon.
• Open or closed when
the membrane
potential changes.

18. • Sodium and potassium gated channels are
therefore voltage – gated ion channel.

19. Process occurs during graded potential

20. • Increase the magnitude of membrane
potential.
• Inside of the membrane becomes more
negative.
• More K+ ions channels open.
• Movement of more K+ to the outside of cell.
• Inside becomes more negative thus more
negative value of potential is produced.

21. • Reduction in the magnitude of membrane
potential.
• Inside of the membrane becomes less
negative.
• More Na+ ions channels open.
• More movement of Na+ into the cell. Inside of
the cell becomes less negative.
• Less negative value of potential is produced.

22. Action Potential

23. Nerve impulse
Nerve impulse of signals that carry information
along the axon.
The transport of information can occur at great
distances, for example, from toes to spinal cord.

24. Action potential is very brief.
• 1-2 millisecond in duration
• Enable a neuron to produce the voltage at
high frequency
• This feature is important as neuron encode
information in their action potential
frequency. For example, knee-jerk reflex
2

25. Action potential frequency
• Related to magnitude and suddenness of
stretch in the quadriceps muscle
3

26. Production of active potential

28. Resting potential
• On Na+ ion channel, activation gate is closed.
Meanwhile, inactivation gate is open in most
channel.
• On K+ ion channel, activation gate is closed.
1

29. Depolarization
• Occur when stimulus is present and
depolarizes membrane.
• On Na+ ion channel, both gates open. Na+
diffuse into the cell. Then Na+ influx causes
further depolarization. More Na+ diffuse into
the cell, so on.
• Inside membrane become less negative.
• On K+ ion channel, activation gate remain
close.
2

30. Rising phase of
the action potential
• Threshold crossed, membrane potential close
to ENa (62 mV) .
• On Na+ ion channel, activation gate is open
and inactivation gate open too.
• On K+ ion channel, activation gate is closed.
3

31. Falling phase of action potential
• On Na+ ion channel, activation gate is open.
Inactivation gate is closed. Which block the
Na+ influx.
• On K+ ion channel, activation gate is open.
Which permit K+ reflux. This caused the inside
of the membrane becomes negative and
membrane potential close to EK, -72 mV.
4

32. Undershoot
• Membrane’s permeability of K+ is higher than at
rest. Membrane potential close to EK.
• On Na+ ion channel, both activation and
inactivation gates are closed.
• On K+ ion channel, the activation gate is open
initially, soon it will closed and increase the
membrane potential to rest potential.
• Second depolarising stimulus occurs during this
period, but it will not able to trigger an action
potential, refractory period.
5

33. Conduction of action potential

34. • Action potential is along distance signal
without diminishing from the cell body to the
synaptic terminals.
• Long distance signals does regenerating.

36. 1
• At the site where action potential is initiated,
the Na+ influx during rising phase creates
electric current that depolarised axon the
neighbouring membrane.
• Depolarisation in neighbouring region is large
enough to reach threshold. This is the point
where action potential is reinitiated.
• This process is repeated many times as action
potential travels the length of axon.

37. 2
• Behind travelling zone of depolarization due to
Na+ influx, this region is known as zone of
repolarization due to K+ efflux.
• At this zone, inactivation gate Na+ channel
closed.
• Inward current that depolarises the axon
membrane ahead of the action potential cannot
produce action potential behind it.
• This prevents action potential from travelling
back toward the cell body.
• Action potential moves in only one direction.

38. 3
• Depolarisation – repolarisation process is
repeated in the next region of the membrane.
• Local current of ions across the membrane
caused action potential to be propagated
along the length of the axon.