Understanding the Heart's Electrical Charge: Origins and Function

[dleacock]

this may be outdated, but I was under the impression that it was an electrical charge that powered the heart to beat. If so, where does the initial charge come from that started this whole process?

thanks
dleacock

 

[matthyaouw]

The Sinoatrial node (or cardiac pacemaker) doesn't power the heart as such (the heart is muscle fibre and is 'powered' about the same as any other muscle in your body, even though it is of a different muscle type to the rest), but it does send the nerve impulses that cause it to contract.

http://en.wikipedia.org/wiki/Cardiac_pacemaker

 

[HallsofIvy]

It would be more accurate to say that the electrical charge "triggers" the muscles. For most of us that electrical charge comes from the autonomic nervous system. For people with pacemakers it comes from a battery.

 

[dleacock]

if the electrical charge comes from the autonomic nervous system, where does that get its charge from? how does it produce an on going charge?

thanks
dleacock

 

[saltydog]

ATP. Am I missin' something?

 

[chroot]

Muscle cells use sugars to produce ATP, which is then used as an energy source throughout the cell -- just like every other cell in the body. The electrical impulses do not power the muscle, they only orchestrate its contractions.

Electrical potentials are created by cells by using the sodium and potassium pumps, which push charged ions through the cell membrane. These pumps operate using energy from ATP.

- Warren

 

[Monique]

The pacemaker cells generate electricity by quickly changing their electrical charge from negative to postive and back (by negatively charged ions traveling out through the cell membrane and positively charged ions traveling in), this electrical charge is then conducted through the heart muscle.

 

[saltydog]

Duh . . . ATP. Really, I think someone should write a complete description of the biochemical apparatus involved from eating a rasberry truffel to doing a pushup. That's right, all the chemistry, all the molecules, all the physiology. Who's takin' Biochemistry in here this semester anyway? Sounds like a good project to me. Few weeks oughta' do it.

 

[DaveC426913]

I wonder if the question is simpler than it seems. Perhaps he's wondering, not about the mechanism, but about the actual voltage/amperage source.

I think saltydog may be closer to the truth than I, but our bodies use Calcium, Potassium, Magnesium and Sodium, all of which like to form ions - thus they have potential differences exploitable by the body.

 

[dleacock]

Thanks for the info, all the posts were helpfull, but DaveC426913 was a bit closer to what I was thinking about. I had just finished a unit on electricity, voltage, ac/dc, induction all that kind of stuff, and I was trying to think about those things in terms of the heart and all the over all charges that happen in the body.

 

[Monique]

ATP. Am I missin' something?

Yes you are, describe to me how ATP leads to an electrical current.

 

[saltydog]

Yes you are, describe to me how ATP leads to an electrical current.

Well ATP is involved in the action potential via the synapse since binding of various neurotransmitters to their receptors involves ATP thus ATP . . . "leads to an electrical current".

 

[Monique]

ATP activates the ATP-sensitive potassium channels, leading to the release of Ca2+ out of the sarcoplasmic reticulum and downstream events.

To put misunderstandings that were raised in this thread out of the world, I have copied a paragraph from this http://www.biofiz.am.wroc.pl/instrukcje/L4muscle.pdf .

Scheme of cardiac conduction system.

Cells of S-A node, A-V node and Purkinje cells can depolarise pontaneously [this is the answer on the question, spontanious depolarization powers the heart] and therefore can act as cardiac pacemakers. The inherent spontaneous rate of depolarisation is progressively slower from the S-A node down to the Purkinje fibres. The rate of action potential firing in S-A node is 78 min-1, in A-V node 50 min-1 and in Purkinje cells 30 min-1.

Cells of sinoatrial node are the primary pacemaker cells of the heart. These cells are characterised as having no normal resting potential – after the action potential the membrane potential successively increases until the threshold potential is reached. This process is called spontaneous depolarisation.

Spontaneous depolarisation is a result of co-operation of several types of channels. When the membrane potential (during repolarisation) reaches –75 mV the cationic channels open and simultaneously the delayed rectifying potassium channels close. In this situation the sodium influx slowly increases the membrane potential until the threshold potential of calcium T-channels is reached (-50 mV). Membrane depolarisation caused by the opening of calcium T-channels activate calcium Lchannels and next action potential is generated.

Action potentials of cardiac cells (pacemakers as well as normal myocytes) are generated by calcium mechanism and therefore they differ from action potential of neurons (sodium mechanism).

 

[saltydog]

Well apparently the discussion is about what controls the beating of the heart and not what is the energy source; the latter of which I believe is ATP. So if I offended anyone by saying "Duh, ATP" I apologize.

Thanks for the reference Monique.