Pacemaker Action Potential In Autorythmic Cells

Lectured by: Dr. Fatima; Management & Science University
Notes by: Malilith F. Ila

Action Potential;
A short-term change in electrical potential on the surface of the cell in response to stimulation, and then leads to the transmission of an electrical impulse that travels across the cell membrane. The electrical membrane potential of the cell rapidly rises and falls, following a consistent trajectory.

- A form of transport through the nervous fibres.
- Change of charge; change in the movements of ions (sodium, potassium, calcium) across the cell membrane.

Resting membrane potential;
The electrical potential of the inside of a cell, relative to its surroundings. Happens when the cell is at rest where there is no action potential initiated.




Extra: Cardiac muscle is independant!






Main Types of Cardiac Muscle Cells
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i) Contractile cells
- 99%
- For contraction
ii) Autorythmic cells
- 1%
- For intitation of action potential
- Non contractile

Pacemaker Action Potential In Autorythmic Cells
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1. Depolarization
- A slow process
- From -60 to -40 (to treshold)
- Going towards positive

i) Decreased passive outflux of K+ [Potassium]
- Less K+ leave the cell membrane due to slow closure of K+ channels
ii) Increased Ca++ [Calcium] influx
- More Ca++ come inside the cell due to opening of T-type calcium xhannels
iii) No changes in Na+ [Sodium]

2. Rising phase in action potential
- A fast process
- From -40 to around 0
- Going towards positive

i) Raise in Ca++ influx in huge amount
- More Ca++ enter the cell membrane due to activation of L-type calcium channel

3. Falling phase of action potential
- A rather fast process
- From around 0 to -60
- Going towards negative

i) Increased outflux of K+ [Potassium]
- K+ exits the cell membrane due to activation of potassium channels.



Reference:
http://www.biology-online.org/dictionary/Resting_potential
http://library.thinkquest.org/03oct/02090/TQEnglish/cardiovascularsystem.htm
http://en.wikipedia.org/wiki/Cardiac_pacemaker
http://en.wikipedia.org/wiki/Cardiac_action_potential
http://en.wikipedia.org/wiki/Cardiac_muscle
http://iws.collin.edu/cdoumen/2402/2402Read/CardiacRead.html [just for my guideline]