what is the chemical composition of the electric impulse from the sinoatrial node?

[lboogy]

Hi everyone,

 

I'd be really grateful if anyone could answer this....I was assuming that it was the flow of electrons that the body somehow manages to break down (as in a flow of electrons being a electrical charge). My lecturer didn't seem to know, my text books don't go into it, and neither does wikipedia etc....does anybody know?

 

thanks in advance!

Gav

[zule]

Could anyone explain me what does “the flow of electrons that the body somehow manages to break down” mean? As my English is not good at all, I don’t know if I understand this phrase: I would say that it means “ruining electrons”, but that doesn’t make sense to me.

 

Anyway, the electric impulse through the cells is not transmitted exactly as through an electric wire. Instead moving electrons, atoms whith a positive charge (cations) are driven from the exterior into the cell.

The cells in repose have potential difference with the cellular exterior; the inner of the cell has a more negative charge. The entrance of Na (+) and Ca(+) into sinoatrial cells change this potential and this prompts the opening of Ca(+) and Na (+) channels in the neighbouring cells. In this way, the neighbouring cells also change the potential and the electric impulse is driven.

[Reaper]

Could anyone explain me what does “the flow of electrons that the body somehow manages to break down” mean? As my English is not good at all, I don’t know if I understand this phrase: I would say that it means “ruining electrons”, but that doesn’t make sense to me.

 

As a person who is fluent in English, don't worry about it, I don't understand the phrase either.

[insane_alien]

well zule, your interpretation would appear to be right from a linguistical(to do with language) though it doesn't make any sort of sense from a physical point of view.

[lboogy]

Zule, thanks for explaining. When I said “the flow of electrons that the body somehow manages to break down” I appreciate I didn't write it the best way. I meant electrons detached from the atoms, but I haven't studied physics since GCSE so maybe I got that wrong too, but I understood electron charge to be a flow of electrons detached from atoms.....correct me if I'm wrong!

[Glider]

I don't think you're wrong in principle, but that's not how it works in the body.

 

Nerve impulses in the body are electrochemical and are based upon the potential created by an imbalance in the distribution of ions across nerve cell membranes.

 

There are three main factors that create a potential across a nerve cell membrane: 1) Neurons contain many large anionic proteins (albumin) that results in an overall negative charge inside the neuron compared to outside. 2) There is a higher concentration of sodium ions outside the cell than inside. 3) There is a higher concentration of potassium ions inside the cell than outside.

 

Because of these factors, neurons have a potential of about -70mv from inside to outside (i.e. the cell is polarised). This is known as the resting potential.

 

A nerve impulse (action potential) occurs when something causes sodium channels to open. When this happens, sodium rushes in and the cell depolarises at that point. This causes a local current at that point in the membrane where there is a potential along (rather than across) the membrane. This causes voltage gatged soduim channels further up the cell to open and so the membrane depolarises further up and the action potential travels along the membrane.

 

As sodium channels close, potassium channels open and potassium rushes out down its concentration gradient. Sodium potassium pumps also work to remove sodium and pump in potassium (3 sodium out to 2 potassium in). These mechanisms reestablish the resting potential.

 

The whole thing is based on the movement of ions, not electrons.

[thedarkshade]

1) Neurons contain many large anionic proteins (albumin) that results in an overall negative charge inside the neuron compared to outside. 2) There is a higher concentration of sodium ions outside the cell than inside. 3) There is a higher concentration of potassium ions inside the cell than outside.

yes, absolutely well said!

This is otherwise called active transport because it requires energy. As it is moving the ions from e place with less concentration to a place with higher concentration, this is not a physical process so it needs energy. And active transport uses about 20% of our energy.:

 

And the speed of nerve impulses is somewhere around [math]120\frac{m}{s}[/math], but pain signals seem to travel only two feet per second, this is why you first feel the pressure, then pain!

[iNow]

As it is moving the ions from e place with less concentration to a place with higher concentration, this is not a physical process so it needs energy. And active transport uses about 20% of our energy.

I remember you using this figure in another post. I am not entirely sure what you mean. Can you elabore, 20% of which energy specifically? Cheers.

 

 

 

Thanks to thedarkshade, I remembered that we have had another good dialog on this topic in the following thread:

 

 

http://www.scienceforums.net/forum/showthread.php?p=369813&post369813

the percentage of the cells energy (where it uses it's ATP) is closer to 50-70% to power the sodium/potassium pump. Again, nearly 70% of all of the nerve cells energy, which it derives from ATP, goes to powering the Na/K pump. Notice also that I said the "cell's" energy, not the "entire body's" energy. This is an important distinction.

[thedarkshade]

I remember you using this figure in another post. I am not entirely sure what you mean. Can you elabore, 20% of which energy specifically? Cheers.

Actually it wasn't me I think who used that figure, I was just quoting someone (I think).

 

And about that 20%, I'm using the words of my professor when saying that.

I guess I have to ask him again for a more detailed explanation, and then I'll get back to you.

 

Thnx iNow

[waffleninja]

this is the article you are looking for

 

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

 

it's mostly sodium and potassium

[zule]

I don't think you're wrong in principle, but that's not how it works in the body.

 

Nerve impulses in the body are electrochemical and are based upon the potential created by an imbalance in the distribution of ions across nerve cell membranes.

 

There are three main factors that create a potential across a nerve cell membrane: 1) Neurons contain many large anionic proteins (albumin) that results in an overall negative charge inside the neuron compared to outside. 2) There is a higher concentration of sodium ions outside the cell than inside. 3) There is a higher concentration of potassium ions inside the cell than outside.

 

Because of these factors, neurons have a potential of about -70mv from inside to outside (i.e. the cell is polarised). This is known as the resting potential.

 

A nerve impulse (action potential) occurs when something causes sodium channels to open. When this happens, sodium rushes in and the cell depolarises at that point. This causes a local current at that point in the membrane where there is a potential along (rather than across) the membrane. This causes voltage gatged soduim channels further up the cell to open and so the membrane depolarises further up and the action potential travels along the membrane.

 

As sodium channels close, potassium channels open and potassium rushes out down its concentration gradient. Sodium potassium pumps also work to remove sodium and pump in potassium (3 sodium out to 2 potassium in). These mechanisms reestablish the resting potential.

 

The whole thing is based on the movement of ions, not electrons.

Sinoatrial node cells don’t work exactly as neurons. In vertebrates, these cells are specialized muscular cells. In the sinoatrial node cells we can’t talk about a stable resting potential, because the membranes of these cells suffer a continued depolarization, named pacemaker potential, which precedes to every action potential.

 

Pacemaker activity originates in time-dependant changes in membrane conductance. Depolarization starts immediately after the previous action potential, when membrane conductance for the K(+) is very high. Then, K(+) conductance goes gradually down and membrane is depolarized due to the existence of a continuous high conductance for the Na(+). Hodking cycle predominates then to produce the fast regenerative ascent of the cardiac action potential.

 

This automatically produced potential is then driven to the neighbouring cells that don’t have the pacemaker function. These neighbouring cells have a real resting potential and they arrive at the action potential thanks to the modulation of Ca(++), Na(+) and K(+) channels.

[thedarkshade]

Ca(++)...

It usually written [math]Ca^{+2}[/math]

[Glider]

Sinoatrial node cells don’t work exactly as neurons. In vertebrates, ...

Yes, I know. I was just making the general point that the whole thing is based on the movement of ions, not electrons.

[Revenged]

i don't think the SA node action potential has been very clearly explained...

 

http://www.biosbcc.net/doohan/sample/images/CO%20and%20MAP/0306pace.jpg

 

SA node action potential

 

- resting potential NOT constant

- threshold potential shown by dashed line

- depolarisation due to Na+ channels opening

- repolarisation due to K+ channels opening

 

heart rate control

 

sympathetic: adrenaline / noradreanline

- increases heart rate by decreasing time taken to reach threshold potential

- mechanism: b1 adrenoreceptors -> increases Na+ influx

 

parasympathetic: acetylcholine

- decreases heart rate by increasing time taken to reach threshold potential

- mechanism: muscarinic acetylcholine receptor (M2) -> increases K+ influx