Physology _Action potential mechanism .pdf

Action potential mechanism

1. The nerve
It is the functional unit of the nervous system

2. Neuron (nerve cell)
Cell body (Soma)
Dendrites
Axon (nerve fiber)
Synaptic knobs
Synapse

3. Surrounding membranes of the nerve
fiber
Plasma membrane
Neurilemma
Myelin sheath
Non myelinatednerve fibers ???

4. Question
There is an electrical potential difference
between inner and outer surfaces of cells,
membrane potential of large nerve cells during
rest is ………
a) +60 mV b)-90 mV
c) -70 mV d) + 50 mV

5. Membrane potential
K+ (140 mEq/L)
Organic anions -
Na + & Cl–
(14 mEq/L)
Na + (142 mEq/L)
Cl-
K+ (4 mEq/L)
Resting membrane potential
-90 millivolts(mV)

6. Causes of the resting membrane
potential
1-Leakage of sodium and potassium
through sodium potassium leak channel:
100 times more permeable to K than Na
Na
K
2-Active transport of Na and K through Na-K pump
+++
3 Na
2 K
+++
3-Organic anions
Phosphate
Sulphate&Prot
ein
---

7. Origin of normal resting membrane
potential
1-Role of K ions -94 mV
2-Role of Na ions + 61 mV
3-Role of Na-K leakage -86 mV
4-Role of Na-K pump -4 mV
-90 mV

8. Excitation
Excitabilityistheabilityoflivingtissuesto
respondtochangesinitsenvironment,these
changesarecalledstimuli.Themostexcitable
tissuesinthebodyarenervesandmuscles.

9. The stimulus
Isanagentorchangeintheenvironment
usedtoexciteacellthrough
depolarizationofitsmembrane
Mechanical
Thermal
Chemical
Osmotic
Electromagnetic
Electrical

10. Electrical stimuli is preferred
They are similar to the nature.
Their intensity and duration can be
easily controlled.
They do not damage the fiber.

11. Action potential
Rapid transient change in cells membrane
potential
Stages:
1-Depolarization
2-Repolarization
3-Negative after potential (After-
depolarization)
4-Positive after-potential (after
hyperpolarization)

12. -ve
+ve

13. Question
How membrane potential can be returned to its
resting polarized state?

14. Re-establishing of the resting
membrane potential
1-OutwarddiffusionofNaandInward
diffusionofKtilltheirconcentration
becomesequalonbothsides.
2-Na-K pump.