Cerberus

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In passage III of TPR exam C BS, it is talking about action potentials and it talks about influx of calcium ions as setting off an action potential. Now this confuses the beejesus out of me because I thought it was Na that flowed into a cell causing an action potential. Can it be either?

</non bio major>
 

UCLAstudent

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It can be either, especially with heart cell action potentials. The fact that positive ions are flowing in is the key. As positive ions flow in, the inside of the cell is becoming more positive with respect to the outside (and thus threshold can be reached). So, yeah, calcium can do that.
 

Cerberus

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Originally posted by UCLAstudent
It can be either, especially with heart cell action potentials. The fact that positive ions are flowing in is the key. As positive ions flow in, the inside of the cell is becoming more positive with respect to the outside (and thus threshold can be reached). So, yeah, calcium can do that.
Thanks, it really threw me off. I heard Ca++ and started thinking they were talking about muscle contraction - i had to reread it about 3 times.
 
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MrTee

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Originally posted by Cerberus
In passage III of TPR exam C BS, it is talking about action potentials and it talks about influx of calcium ions as setting off an action potential. Now this confuses the beejesus out of me because I thought it was Na that flowed into a cell causing an action potential. Can it be either?

</non bio major>
They were probably talking about when the AP gets to the end of the axon, calcium enters and causes release of the Ach vesicles into the synaptic cleft. Along the length of the axon, its mainly na and k causing the AP.
 

fun8stuff

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i don't have time to look this up, but i thought it was Na+ flows in and then Ca2+ flows and it is the reason for the "plataeued" or sustained action potential for skeletal

for cardiac i thought it was ca2+ that starts the AP... it binds to tropomyocin or whatever...
 

fun8stuff

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Originally posted by Drakensoul
Lumen is the cavity of a hollow organ.

E.g: The lumen of a vein is the hollow center of it.
isn't the Ca2+ in the lumen of the sarcoplasmic reticulum?
 

UCLAstudent

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Originally posted by fun8stuff
i don't have time to look this up, but i thought it was Na+ flows in and then Ca2+ flows and it is the reason for the "plataeued" or sustained action potential for skeletal

for cardiac i thought it was ca2+ that starts the AP... it binds to tropomyocin or whatever...
The Ca++ maintaining the "plateau" is for cardiac. The Ca++ binding to tropomyosin is for skeletal muscle (actually, for any type of muscle, I believe).
 

shock827

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Originally posted by UCLAstudent
The Ca++ maintaining the "plateau" is for cardiac. The Ca++ binding to tropomyosin is for skeletal muscle (actually, for any type of muscle, I believe).
Not all types of muscle use tropomyosin. I believe off the top of my head smooth uses calmodulin... i dunno.
 

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Calcium binds to troponin, not tropomyosin.

Calcium is found in the lumen (hollow inside) of the sarcoplasmic reticulum, until it is released to trigger the crossbridge formation.
 

UCLAstudent

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Right, my bad, it binds to troponin and causes the tropomyosin to shift to expose the binding sites.
 

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The action potential in the cardiac muscle is initiated by Na+ and it is maintained for a long plateau by Ca2+.

Also there is contraction-coupling in the cardiac muscle due to Ca2+ which causes complete saturation of troponin binding sites. The MAJOR difference between the contraction of a cardiac cell and a skeletal muscle cell is that Ca2+ in the latter is released from the sarcoplasmic reticulum only, where as in the cardiac cell Ca2+ comes from the ECF and SR.
 

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Originally posted by thekegalman
The action potential in the cardiac muscle is initiated by Na+ and it is maintained for a long plateau by Ca2+.

Also there is contraction-coupling in the cardiac muscle due to Ca2+ which causes complete saturation of troponin binding sites. The MAJOR difference between the contraction of a cardiac cell and a skeletal muscle cell is that Ca2+ in the latter is released from the sarcoplasmic reticulum only, where as in the cardiac cell Ca2+ comes from the ECF and SR.
I could be an ignorant bio major, but this confounds me: what is ECF and SR?
 

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Originally posted by Drakensoul
Extracellular Fluid.
All these bio abbreviations. That was how, on particular event, I saw ORF and began to wonder, "What the heck does this stand for?" only to joggle my brain and remember it was the tired open reading frame :laugh: .
 

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The function of the intercalated disks (also known as desomosomes or tight junctions) is to maintain syncytium
(to cause multiple cells to behave as one cell).

If there is no syncytium , all the cardiac cells will not contract at the same time.
 

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thekegelman, you know alot of biology. I guess you are bio major.

I think you are going to get a 15 on the BS section, honestly.:cool:
 

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i am actually a biochem major. My 15 on the BS will depend on my organic chem skills.

But I am a TA for a physiology class at my school; so thats y i know it.

:)
 
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