The document discusses action potentials and how neurons conduct impulses. It explains that action potentials are rapid changes in membrane potential that allow neurons and muscles to communicate. Action potentials are initiated when stimuli open sodium channels, allowing sodium to rush into the cell and depolarize the membrane. Potassium channels then open, repolarizing the membrane back to its resting potential. This process allows impulses to propagate down axons via changes in membrane potential driven by ion fluxes.

1. 24 Oct. 2012 Ashok Solanki 1
Action Potentials-
the language of excitable tissue
How neurons conduct impulses
How the muscle contract?
How the heart pump?

2. Resting membrane potential created
by semi-permeable membrane and
ions
• Intracellular
– Na 50
– K 400
– Cl 52
• Resting membrane
potential created by semi-
permeable membrane
and ions
• Intracellular
– Na 50
– K 400
– Cl 52
2Ashok Solanki24 Oct. 2012

3. Cell – the functional unit.
• 100 trillion cells organize systems of the body.
Ashok Solanki 324 Oct. 2012

4. 4Ashok Solanki24 Oct. 2012

5. Ashok Solanki 524 Oct. 2012

6. AP OBEYS ALL OR NONE LAW
ALL-OR-NONE RESPONSE
A stimulus below the
threshold also will not
stimulate the neuron
once a threshold limit is
reached any stronger
stimulus will not increase
the cell's response
24 Oct. 2012 6Ashok Solanki

7. 24 Oct. 2012 Ashok Solanki 7
What starts an Action Potential??
• STIMULATION (chemical, electrical, mechanical)
opens Na+ channels
– low intensity stimulation opens few channels,
– local, graded potential
– resting potential restored without action potential

8. 8Ashok Solanki24 Oct. 2012

9. THE NEURON MEMBRANE AT REST
• Neuron maintains a resting membrane
potential of about -70 millivolts across the
cell membrane
• Sodium(Na+) and potassium(K+) are the main
ions involved
• Na+ and K+ cannot pass through the lipid
bilayer membrane
• move through the membrane by using
24 Oct. 2012 9Ashok Solanki

10. ACTION POTENTIAL
• What is it?
• Excitable tissue.
• All or none law of A.P.
• Change in RMP.
• Role of ions?
• Propagation of.
• Propreties of A.P.
10Ashok Solanki24 Oct. 2012

11. Distribution of important ions in ECF & ICF
Na+ K+ Cl-
INSIDE 14 mEq / L 120 mEq / L 8 mEq / L
OUTSIDE 142 mEq / L 4.5 mEq / L 107 mEq / L
24 Oct. 2012 11Ashok Solanki

12. Ashok Solanki 1224 Oct. 2012

13. 24 Oct. 2012 13Ashok Solanki

14. 24 Oct. 2012 Ashok Solanki 14
Action Potential
• ALL-OR-NONE phenomenon
• All Action Potentials are the same intensity.
– stronger sensations result from more
impulses, not stronger impulses.
– more impulses from same neuron
– more impulses from many neurons

15. Na+ / K+ PUMP
Membrane proteins actively transport sodium
out of the cell
potassium in Three Na+ are pumped out for
every two K+ pumped in
result is the cell has more Na+ on the outside
and more K+ on the inside
24 Oct. 2012 15Ashok Solanki

16. 16Ashok Solanki24 Oct. 2012

17. 17Ashok Solanki24 Oct. 2012

18. 24 Oct. 2012 Ashok Solanki 18
How neurons conduct impulses:
• Membrane potential (as
seen in muscle cells)
• K+ diffuses out of neurons
faster than Na+ diffuses
in,
• Na-K pump moves 3Na+
back out for 2K+ back in
• Cl-, phosphate, protein
anions balance cations
• “Resting potential”
= - 70 mV

19. 24 Oct. 2012 19Ashok Solanki

20. 24 Oct. 2012 Ashok Solanki 20
How neurons conduct impulses:
• Action potential
– describes events at one
point of nerve fiber
– 1: stimulus to
threshold potential
– 2: Na+ channels
open, Na+ diffuses in
• Polarity briefly
reversed, to +30 mV
– 3: Na+ channels close

21. 24 Oct. 2012 21Ashok Solanki

22. The Lipid Barrier of the Cell Membrane, and Cell Membrane Transport
Proteins
• Active Transport" of Substances Through Membranes
• Primary Active Transport and Secondary Active Transport
• Co-Transport of Glucose and Amino Acids Along with Sodium Ions
• Sodium Counter-Transport of Calcium and Hydrogen Ions
• Na+-K+ pump performs a continual surveillance role in maintaining
normal cell volume.
• A Positive-Feedback Cycle Opens the Sodium Channels
• Threshold for Initiation of the Action Potential
• A major function of the voltage-gated calcium ion channels is to
contribute to the depolarizing phase on the action potential in
some cells
22Ashok Solanki24 Oct. 2012

23. Ashok Solanki 2324 Oct. 2012

24. 24 Oct. 2012 Ashok Solanki 24
What starts an Action Potential??
• STIMULATION opens
Na+ channels
– higher magnitude
stimulation opens more
channels, local potential
exceeds threshold at
trigger zone,
– Na+ floods in
depolarization

25. Ashok Solanki 2524 Oct. 2012

26. STIMULATED NEURON
Nerve cells are unique in their ability to carry a signal
using membrane potential changes
Stimulation of a neuron opens some of the membrane
proteins (a.k.a. Na+gates)
allows Na+ to pass freely into the cells
free flow of Na+ into the cell causes a reversal of
membrane polarity
polarity reversal is called the action potential
24 Oct. 2012 26Ashok Solanki

27. Resting Potential
• At rest, the inside of the cell is at -70 microvolts
• With inputs from dendrites inside becomes more positive
• If resting potential rises above threshold, an action potential
starts to travel from cell body down the axon
• Figure shows resting axon being approached by an AP
24 Oct. 2012 27Ashok Solanki

28. How Neurons Communicate
• Action Potential is the electrical process
that neurons use to communicate with
each other
• Action Potentials are based on movements
of ions (charged particles) between the
outside and inside of the axon
• Action Potential is an All or Nothing Process
(like a gun firing)
24 Oct. 2012 28Ashok Solanki

29. 24 Oct. 2012 Ashok Solanki 29
Conduction of an Action Potential
• Propagation of A.P. along neuron membrane
• Na+ diffuses, attracted to negative charges in
front of impulse
• A.P. at "A"

30. 24 Oct. 2012 Ashok Solanki 30
What Keeps Impulse Going
the Same Way ?
• Limits to stimulation of neuron/membrane
• Absolute Refractory Period
• Relative Refractory Period

31. Ashok Solanki 31
35. Regarding the ionic basis of action
potential
in cardiac muscle cells, which one of the
following is incorrect?
A. Phase 0: Na influx
B. Phase 1: K influx
C. Phase 2: Ca influx
D. Phase 3: K efflux
24 Oct. 2012

32. GOLDMAN–HODGKIN–KATZ
EQUATION
• V = 60mV log10 PNaNao
• + + PKKo
• + + PClCli
• −
• _________ ________
• PNaNai
• + + PKKi
• + + PClClo
Ashok Solanki 3224 Oct. 2012

33. 24 Oct. 2012 Ashok Solanki 33
How neurons conduct impulses:
– 3: K+ channels open,
K+ diffuses out,
Potential returns to
zero
– 4: All channels
closed, Na-K pump
moves Na+ back out
& K+ back in
– Hyperpolarization
– Resting potential
restored

34. 24 Oct. 2012 Ashok Solanki 34
How neurons conduct impulses:
• Action potential
– describes events at one
point of nerve fiber
– 1: stimulus to
threshold potential
– 2: Na+ channels open,
Na+ diffuses in
• Polarity briefly
reversed, to +30 mV
– 3: Na+ channels close

35. Two Ionic Equilibria and Resting Membrane
Potentials
• The resting membrane potential plays a
central role in the excitability of nerve and
muscle
• An action potential is a rapid change in the
membrane potential followed by a return to
the resting membrane potential
35Ashok Solanki24 Oct. 2012

36. Generation and Conduction of Action Potentials
• An action potential is propagated with the same
shape and size along the whole length of a nerve
or muscle cell
• The action potential is the basis of the signal-
carrying ability of nerve cells
• In muscle cells, an action potential allows the
entire length of these long cells to contract
almost simultaneously.
• Voltage-dependent ion channel proteins in the
plasma membrane are responsible for action
potentials.
36Ashok Solanki24 Oct. 2012

37. Ashok Solanki 3724 Oct. 2012

38. Ashok Solanki 3824 Oct. 2012

39. Ashok Solanki 3924 Oct. 2012

40. Voltage dependent ion channels
• Extracellular Na activation gate with
intracellular inactivation gate and slow K
activation gait
• Conformational changes due to membrane
potential changes influence ion permeability
40Ashok Solanki24 Oct. 2012

41. 41Ashok Solanki24 Oct. 2012

42. Nomenclature
• Polarized membrane: Intracellular potential is
negative relative to extracellular space
• Depolarization = less polarization of the
membrane -80mV -> +20mV
• Hyperpolarization = more polarization of
membrane -80mV -> -100mV
42Ashok Solanki24 Oct. 2012

43. Cell membrane
• Necessary for life as we know it
• Border role for cell
– Separates intracellular from extracellular milleau
• Allows ion and protein concentration
gradients to exist
– Creates electric charge gradients
43Ashok Solanki24 Oct. 2012

44. LECTURE SUMMARY
Ashok Solanki 4424 Oct. 2012