our presentation

1. A Presentation on the topic of
ACTION POTENTIAL

2. WHAT IS ACTION POTENTIAL??
The change in electrical potential associated with the passage of an
impulse along the membrane of a muscle cell or nerve cell.
An action potential occurs when the membrane potential of a specific
axon location rapidly rises and falls: this depolarisation then causes
adjacent locations to similarly depolarise.

3. BIOPHYSICAL BASIS OF ACTION POTENTIAL
Action potentials result from the presence in a cell's membrane of special
types of voltage-gated ion channels. A voltage-gated ion channel is a
cluster of proteins embedded in the membrane that has three key
properties:
 It is capable of assuming more than one conformation.
 At least one of the conformations creates a channel through the
membrane that is permeable to specific types of ions.
 The transition between conformations is influenced by the membrane
potential.

4. Ion movement during an action potential.
Key: a) Sodium (Na+) ion. b) Potassium (K+) ion. c)
Sodium channel. d) Potassium channel. e) Sodium-

5. STAGES OF ACTION POTENTIAL
There are six stages of Action Potential. They are:
1. Resting stage
2. Depolarization stage
3. Repolarization stage
4. Spike potential
5. Negative after potential
6. Positive after potential or Hyperpolarization

6. Figure: Different stages of Action Potential

7. 1. Resting stage: This is the resting membrane potential before the
action potential begins. The membrane is said to be “Polarized” during
this stage because of the very large membrane potential that is
present.
2. Depolarization stage: When the negativity of the membrane potential
rises rapidly in positive direction due to influx (enter) of sodium ions is
called depolarization stage.

8. 3. Repolarization stage: Immediately after depolarization the negativity of
the membrane potential re-establishes towards the normal negative
membrane due to efflux of potassium ion. This is called the repolarization
membrane.
4. Spike potential: Initially , the depolarization wave over shoots the zero
line and then sharply falls. This sharp rise of the depolarization wave and
the rapid fall of repolarization wave is called spike potential.

9. 5. Negative after potential: At the termination of spike potential , the
membrane potential sometimes fails to reach the normal resting stage. This
is called negative after potential.
6. Positive after potential: Sometimes the negativity of membrane
potential become more than its normal level. This is called positive after
potential.

10. Function of an action potential
An action potential is part of the process that occurs during the firing
of a neuron. During the action potential, part of the neural membrane
opens to allow positively charged ions inside the cell and negatively
charged ions out. This process causes a rapid increase in the
positive charge of the nerve fibe.

11. What happens during an action potential?
When an action potential happens, the sodium (Na+) ion channels
(here shown in green) on the axon open and the Na+ rushes in. Since
the Na+ (red) is positively charged, it makes the inside of the axon a
little more positively charged. The sodium keeps rushing in until the
inside is positive relative to the outside.

12. Example of an action potential
The most famous example of action potentials are found as nerve
impulses in nerve fibers to muscles. Neurons, or nerve cells, are
stimulated when the polarity across their plasma membrane
changes. The polarity change, called an action potential, travels
along the neuron until it reaches the end of the neuron