Action potential
-
Upload
jinny-shaw -
Category
Technology
-
view
1.970 -
download
3
Transcript of Action potential
![Page 1: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/1.jpg)
ACTION POTENTIAL
![Page 2: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/2.jpg)
OVERVIEW OF A NERVE IMPULSE
1.Resting potential – neuron is not stimulated at threshold level2.Action potential – neuron responds to stimulus, sends “message” along axon
a. Depolarization
b. Repolarization
** Potential = difference in charge (measured in volts)
![Page 3: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/3.jpg)
RESTING POTENTIAL
Inactive neuron Inside cell membrane – more K+ ions Outside cell membrane – more Na+ ions Polarized cell membrane
Inside cell membrane – negative charge Outside cell membrane – positive charge
Cell membrane relatively impermeable to both ions
![Page 4: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/4.jpg)
WHY IS MEMBRANE POLARIZED AT REST?
1. Na+/K+ pump maintains ion distribution - transports 3 Na+ out and 2 K+ in
2. K+ diffuses out faster – membrane is more permeable
3. Na + is attracted to cell because of its concentration gradient
4. Membrane is impermeable to large negatively charged ions
![Page 5: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/5.jpg)
RESTING POTENTIAL
![Page 6: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/6.jpg)
ACTION POTENTIAL = NERVE IMPULSE
Occurs in excitable membranes – neurons and muscle fibers
Critical level must be reached (“threshold”) before impulse is sent Positive feedback mechanism All-or-none response
Lasts a few milliseconds 2 steps:
Depolarization Repolarization
![Page 7: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/7.jpg)
DEPOLARIZATION
Stimulus causes adjacent Na+ ion channels to open along axon
Na+ ions rush into cell (high low concentration)
Movement of Na+ ions reverses the charge of the membrane (depolarization):
Inside cell membrane – positive charge Outside cell membrane – negative charge
If threshold is reached, adjacent Na+ ion channels to open along axon
![Page 8: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/8.jpg)
DEPOLARIZATION
![Page 9: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/9.jpg)
REPOLARIZATION
K+ ion channels open K+ ions rush out of cell (high low concentration)
Restores polarization of cell membrane Inside cell membrane – negative charge Outside cell membrane – positive charge
Ion distribution is different than at resting potential – can’t send another impulse yet
Inside cell – low K+, high Na+
Outside cell – high K+, low Na+
![Page 10: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/10.jpg)
REPOLARIZATION
![Page 11: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/11.jpg)
AFTER REPOLARIZATION
Na+/K+ pump corrects ion distribution Inside cell – high K+, low Na+
Outside cell – low K+, high Na+
Another impulse can now occur
![Page 12: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/12.jpg)
ROLE OF MYELIN
Myelin insulates the axon Action potential must “jump” from node
to node Saltatory conduction
Action potential is MUCH faster than along an unmyelinated axon
![Page 13: Action potential](https://reader038.fdocuments.in/reader038/viewer/2022102901/55506eb5b4c905cc0f8b4a8a/html5/thumbnails/13.jpg)
FACTORS AFFECTING NERVE IMPULSE Local anesthetics – block Na+ channels – no Na+
movement = no AP Continuous cold and/or pressure – blocks circulation (flow
of nutrients and oxygen), so there is no energy for Na+/K+ Pump = no AP