Your SlideShare is downloading. ×
0
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Ch04
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Ch04

385

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
385
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
28
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. THE ACTION POTENTIAL
  • 2. ACTION POTENTIALConveys information over distance in the nervous systemRapid reversal of the membrane potential at rest
  • 3. ACTION POTENTIALThe Generation of an Action Potential is caused by depolarization of themembrane beyond threshold“All-or-none” eventChain reactione.g., Puncture foot, stretch membrane of nerve fibersOpens Na+-permeable channels Na+ influx depolarizedMembrane reaches threshold action potential
  • 4. ACTION POTENTIALA way to study the properties of AP is the Generation of Multiple Action Potentials Artificially - inject current into a neuron using a microelectrode
  • 5. ACTION POTENTIALFiring frequency reflects the magnitude of the depolarizing currentThe maximum firing frequency is 1000 Hz. This means that after an AP, is notpossible to initiate another one for at least 1 msec (absolute refractory period).Also the initiation of another AP after few msec requires more current(relative refractory period).
  • 6. THE ACTION POTENTIAL IN THEORYIf only K+ channel are open then the membrane would reach EK+
  • 7. THE ACTION POTENTIAL IN THEORYBut if the membrane is also permeable to Na+ , the EP will go towards ENa+ Rising phase (depolarization): Inward sodium current Falling phase (repolarization): Outward potassium current
  • 8. THE ACTION POTENTIAL IN REALITYFirst described by Hodgkin and Huxley, with the use of a voltage Clamp: “Clamp”membrane potential at any chosen value Rising phase  transient increase in gNa, influx of Na+ ions Falling phase  increase in gK, efflux of K+ ions Existence of sodium “gates” in the axonal membrane sensitive to change in membrane potential and selective for Na
  • 9. THE ACTION POTENTIAL IN REALITYThe Voltage-Gated Sodium Channel 1) sensitivity to change in membrane potential 2) selectivity for Na
  • 10. THE ACTION POTENTIAL IN REALITYThe Voltage-Gated Sodium Channel Open with little delay Stay open for about 1msec Cannot be open again by depolarization (Absolute refractory period: Channels are inactivated)
  • 11. THE ACTION POTENTIAL IN REALITYThe Voltage-Gated Potassium Channels Open in response to depolarization but later than sodium gates Potassium conductance serves to rectify or reset membrane potential (Delayed rectifier) Structure: Four separate polypeptide subunits join to form a pore
  • 12. THE ACTION POTENTIAL IN REALITY To summarize- Key Properties of the Action Potential are •Threshold •Rising phase •Overshoot •Falling phase •Undershoot •Absolute refractory period •Relative refractory period
  • 13. THE ACTION POTENTIAL CONDUCTIONDown axon to the axon terminal Orthodromic: Action potential travels in one direction Antidromic (experimental): Backward propagationTypical conduction velocity: 10 m/sec and length of action potential: 2 msec
  • 14. THE ACTION POTENTIAL CONDUCTIONFactors Influencing Conduction Velocity: 1) Spread of action potential along membrane follows the path of less resistance. It depends upon axon structure and direction of positive charge 2) Path of the positive charge Inside of the axon (faster) Across the axonal membrane (slower) 3) Axonal excitability Axonal diameter (bigger = faster) Number of voltage-gated channels opens
  • 15. THE ACTION POTENTIAL CONDUCTIONLayers of myelin sheath facilitates current flow (saltatory conduction) Myelinating cells 1) Schwann cells in the PNS 2) Oligodendroglia in CNS
  • 16. THE ACTION POTENTIAL CONDUCTIONSaltatory conduction 0.2 - 2 mm
  • 17. THE ACTION POTENTIAL INITIATION

×