1. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

Dismiss Notice
Hey Texans—join us for a DFW meetup! Click here to learn more.

Action Potential

Discussion in 'MCAT Study Question Q&A' started by wheyprotein, May 14, 2008.

  1. wheyprotein

    2+ Year Member

    Joined:
    Nov 2, 2007
    Messages:
    41
    Likes Received:
    0
    Status:
    Pre-Medical
    Could anyone explain in simple terms the concept of action potential in the context of the nervous system? If this question has already been answered in another forum, please direct me to the link. Thank you.
     
  2. Note: SDN Members do not see this ad.

  3. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    I ll try my best to explain.

    When a neuron gets depolarized sodium gated ion channels open allow for Na+ to enter at the same time K+ are slowly trickeling out because K+ is permeable to the neuron. Once the depolarization reaches -50mV the threshold value and action potential will occur. It is an all or none response that will spike up. So the spike is the action potential. Then like what goes up must come down right so the spike, begins to asend downwards the K+ ion channels open while the Na channels begin to close. This allows more K+ ions to leave the cell than before which makes the inside of the cell more and more negative a term we use is repolarized. There is a point during this time that the cell will pass its resting potential of -70mV and no additional impulse will cause an action potential we call this the refactory period. Once the cell reaches its normal state of -70mV it will be ready for another impulse.

    Did it help?
     
  4. RySerr21

    RySerr21 i aint kinda hot Im sauna
    10+ Year Member

    Joined:
    Dec 22, 2007
    Messages:
    5,931
    Likes Received:
    23
    Status:
    Fellow [Any Field]
    just to add...that point is also known as hyperpolarization. the cool stuff is when you start talkin about how that action potential is transferred from the neuron to the muscle to stimulate muscle contraction....thats when the fun begins!!!! i imagine if you are doin neuron action potential the muscle stuff cant be far behind.
     
  5. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    Your right the party in the Muscles. Hey im doing this off the top of my head but if i say somthing wrong let me know dont want people hating lolz.:D

    Alright so the action potential releases neurotransmitter into nueromusuclar junction travels throughout the muscel fiber by t-tubules and causes deploarization of the sarcolemma and enters SR (sarcoplasmic reticulum) which release wave of Ca+ . Calcium changes troponin into tropomyosin which was blocking the active site for myosine (thick filament). Now tropomyosin is removed from actin so the myosin head can attach its head. When that happens ADP losses a P causes a power stroke. Then the head of myosin is detached with ATP is added.
     
  6. wheyprotein

    2+ Year Member

    Joined:
    Nov 2, 2007
    Messages:
    41
    Likes Received:
    0
    Status:
    Pre-Medical
    Thanks, Zerconia.

    Your explanation helped just a bit. I think that before I can fully understand what you wrote, I need to aska more basic question. What is the Na+/K+ pump? What use does it have? Why is is mentioned throughout the Bio texts? Any help would be appreciated.

    Thanks.
     
  7. Kaustikos

    Kaustikos Archerize It
    7+ Year Member

    Joined:
    Jan 18, 2008
    Messages:
    12,216
    Likes Received:
    4,156
    Troponin doesn't change into tropomysosin. Troponin interacts with tropomyosin. But otherwise, spot on.
     
  8. scottyT

    scottyT Real Member
    10+ Year Member

    Joined:
    Mar 19, 2006
    Messages:
    412
    Likes Received:
    0
    MDApps:
    Status:
    Medical Student

    Out: K K K K K K K K
    ----------------------
    ----------------------
    In: NaNaNaNaNaNaNaNaNa

    After the cell depolarizes you have the above diagram. This potential is positive so an action potential has occurred (look up the Nernst equation if you'd like to know why the potential flip-flops). The Na/K pump speeds recovery so the neuron can get ready to fire again. It is used to quickly move K ions back in and Na ions out to restore the negative resting potential. The pump moves two K in for every three Na out (cost=1ATP). This is because the membrane is more permeable to Na than K, ie, Na makes its way back in quicker.

    On a side note the resting membrane potential would ultimately be restored even if the pump didn't work, this is what ouabain does. It would just take longer to restore.
     
  9. RySerr21

    RySerr21 i aint kinda hot Im sauna
    10+ Year Member

    Joined:
    Dec 22, 2007
    Messages:
    5,931
    Likes Received:
    23
    Status:
    Fellow [Any Field]
    edit: not sure if this is what you were implying, but couldnt tell. the nuerotransmitter doesnt ravel through the muscle fiber. it attaches to a chemical-gated sodium channel on the oustide which allows sodium to rush down the sarcolemma, t tubules, etc.

    1) the action potential travles down the sarcolemma and then down the T-tubules.... the T-Tubules are just the name for the part of the sarcolemma that is going inwards towards the sarcoplasmic reticulum.

    2) troponin isn't changed into tropomyosin. there is a troponin-tropomyosin complex. at rest, troponin is blocking the myosing heads from binding to tropomysosin. Calcium binds to troponin, causing a conformational shift which frees the spot where the myosin heads are supposed to grab on to tropomyosin.

    rest sounds good :thumbup:. ATP is necessary for the release of the myosin head. i think thats what your last sentence was saying, but just checking.
     
  10. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    Thanks guys for the editing really apperciate it.
     
  11. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    When you think about the Na+/K+ pump think of it after an impulse has occured and the neuron is returing back to its resting state. If you understand that then the Na+/K+ pump will make sense.

    So we know a at -70mV the neuron is at rest right. At rest would mean there are more Na+ ions on the outside and more K+ ions inside. (K+ is permeable to the neuron so it goes in and out). So you would think how did we end up like this after a stimulus?

    Well thats where the Na+/K+ pumps comes into play. It keeps the irregular imbalance of the ions by pumping out three Na+ ions for every two K+ ion. (by active transport)
     
  12. RySerr21

    RySerr21 i aint kinda hot Im sauna
    10+ Year Member

    Joined:
    Dec 22, 2007
    Messages:
    5,931
    Likes Received:
    23
    Status:
    Fellow [Any Field]
    the sodium potassium pump is the basis for life!!!!! not really. but peep this....surely you have heard of metabolism. people can have a higher or lower metabolism right? youve probably known someone that has a high metabolism and can eat anything in the world and never gain weight....weeeeeeeell did you know that 70% of your total caloric expenditure is determined by your resting metabolic rate?? and that your resting metabolic rate is largely determined by the activity of the Na/K pump??? pretty cool huh??

    and if you think about it, it makes sense. someone else already described how Na/K pump is used to restore the resting membrane potential. so you could guess that the Na/K potassium pump will be more numerous in tissues like muslce as compared to tissues like fat b/c muscle is WAY more active than fat.....right? so if you are lean and have less fat compared to muscle, you will have more Na/K pumps constantly working and therefore a higher metabolism. that explains why an obese person will have a slower metabolism than a fit person (they have more fat, less Na/K pumps). it also explains why if you exercise you will increase your metabolism (more stimulus for Na/K to work) and why if you go on a diet and restrict your calories greatly your metabolism will decrease. it decreases b/c when you restrict your claories, you lose some fat, but you also lose glycogen from your muscles (your lean tissue). if you are losing lean tissue, you are losing those precious Na/K pumps that we already said play a huge role in your metabolism.


    physiology is so friken cool.
     
  13. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    That is so awsome never thought about the pump that way it makes so much sense now. ryserr:thumbup:
     
  14. evomase

    5+ Year Member

    Joined:
    Mar 9, 2009
    Messages:
    7
    Likes Received:
    0
    Status:
    Dental Student
    .
     
    #13 evomase, Aug 22, 2011
    Last edited: Aug 22, 2011

Share This Page