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Now i'm confused (bio q)

Discussion in 'MCAT Discussions' started by Cerberus, Mar 24, 2004.

  1. Cerberus

    Cerberus Heroic Necromancer
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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>
     
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  3. UCLAstudent

    UCLAstudent I'm a luck dragon!
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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.
     
  4. Cerberus

    Cerberus Heroic Necromancer
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    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.
     
  5. MrTee

    MrTee Senior Member
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    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.
     
  6. Cerberus

    Cerberus Heroic Necromancer
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    OOH! Heres another! (It's not in my Kaplan bio book:() wtf? is the lumen?
     
  7. Drakensoul

    Drakensoul Senior Member
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    Lumen is the cavity of a hollow organ.

    E.g: The lumen of a vein is the hollow center of it.
     
  8. fun8stuff

    fun8stuff *hiding from patients*
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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...
     
  9. fun8stuff

    fun8stuff *hiding from patients*
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    isn't the Ca2+ in the lumen of the sarcoplasmic reticulum?
     
  10. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    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).
     
  11. shock827

    shock827 Senior Member
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    Not all types of muscle use tropomyosin. I believe off the top of my head smooth uses calmodulin... i dunno.
     
  12. Drakensoul

    Drakensoul Senior Member
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    Ca+2 is stored in the sarcoplasmic reticulum of muscle cells (in the lumen).
     
  13. jalabert

    jalabert Member
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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.
     
  14. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    Right, my bad, it binds to troponin and causes the tropomyosin to shift to expose the binding sites.
     
  15. ASDIC

    ASDIC The 9th Flotilla
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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.
     
  16. researchprof

    researchprof Senior Member
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    I could be an ignorant bio major, but this confounds me: what is ECF and SR?
     
  17. researchprof

    researchprof Senior Member
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    Crap. SR is sarcoplasmic recticulum, but ECF?:confused:
     
  18. Drakensoul

    Drakensoul Senior Member
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    Extracellular Fluid.
     
  19. researchprof

    researchprof Senior Member
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    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: .
     
  20. ASDIC

    ASDIC The 9th Flotilla
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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.
     
  21. researchprof

    researchprof Senior Member
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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:
     
  22. ASDIC

    ASDIC The 9th Flotilla
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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.

    :)
     
  23. Drakensoul

    Drakensoul Senior Member
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    Yeah, most of this stuff is covered in A&P classes. Not so much in the Core Bio series.
     

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