Notices
Results 1 to 8 of 8
Like Tree2Likes
  • 1 Post By Cogito Ergo Sum
  • 1 Post By Strange

Thread: The Heartbeat

  1. #1 The Heartbeat 
    New Member
    Join Date
    Sep 2013
    Posts
    2
    This question has been nagging me for a long time: what directly causes the heartbeat we feel when we put our hand "over our heart"?
    Firstly, the heartbeat correlates with the heart contracting, meaning the volume of the heart decreases. This means the heartbeat cannot be directly attributed to the contraction of the heart, right?
    Secondly, if the heartbeat were caused by a pulse, how are we able to feel the pulse through the ribcage? Or is the pulse outside of the ribcage, if the heartbeat is caused by a pulse?
    Thank you everyone ahead of time for taking the time to read and answer my question!


    Reply With Quote  
     

  2.  
     

  3. #2  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    17,036
    Quote Originally Posted by BaneOfGodot View Post
    Firstly, the heartbeat correlates with the heart contracting, meaning the volume of the heart decreases. This means the heartbeat cannot be directly attributed to the contraction of the heart, right?
    I'm not sure why you think the heartbeat can't be attributed to the contraction of the heart muscles? It is the just vibration produced as the heart contracts and expands. It does this quite forcefully as it has to pump blood through the entire body.

    Secondly, if the heartbeat were caused by a pulse, how are we able to feel the pulse through the ribcage? Or is the pulse outside of the ribcage, if the heartbeat is caused by a pulse?
    What do you mean by "pulse" in this context?


    ei incumbit probatio qui dicit, non qui negat
    Reply With Quote  
     

  4. #3  
    Forum Masters Degree mat5592's Avatar
    Join Date
    Mar 2013
    Location
    West Virginia
    Posts
    601
    The actual sound of a heartbeat is a result of the AV and semilunar valves closing.

    Also your pulse is created by your heartbeat, not the other way around.
    Reply With Quote  
     

  5. #4  
    Moderator Moderator Cogito Ergo Sum's Avatar
    Join Date
    Jun 2013
    Location
    Belgium
    Posts
    2,519
    Quote Originally Posted by BaneOfGodot View Post
    what directly causes the heartbeat we feel when we put our hand "over our heart"?

    The contraction and relaxation of the atria and ventricles.

    Quote Originally Posted by BaneOfGodot View Post
    Firstly, the heartbeat correlates with the heart contracting, meaning the volume of the heart decreases. This means the heartbeat cannot be directly attributed to the contraction of the heart, right?

    There are actually two "beats" (audible heart sounds) in one cardiac cycle (the number of cardiac cycles/min determines the heart rate).
    The first sound ('lub') is associated with the closure of the atrioventricular valves, or the moment that the ventricles are filled with blood due to the fact that the atria contracted.
    The second sound ('dub') is associated with the closure of the semilunar valves, or the moment that ventricles are empty after they contracted and ejected blood into the arteries.

    I think the confusion is caused by the fact that these two sounds and both the contractions happen very fast (200-400 ms) and you feel just one contraction (if you are not familiar with the structure of the heart, then I recommend you to study this image).

    Quote Originally Posted by BaneOfGodot View Post
    Secondly, if the heartbeat were caused by a pulse, how are we able to feel the pulse through the rib cage? Or is the pulse outside of the ribcage, if the heartbeat is caused by a pulse?

    The cardiac cycle is series of contractions and relaxations.
    These are caused by an electrical pulse, which originates from a highly specialized group of cells in the heart: autorhythmic cells (or pacemakers).
    This pulse is not detectable by touch, but it can be visualized via an ECG (electrocardiogram).


    I hope I have answered your question in a satisfying way. If not, feel free to ask more questions.


    Source:
    Silverthorn, D.U. (2012), "Human Physiology: An Integrated Approach, 6th Edition", Pearson, Ch. 14
    Last edited by Cogito Ergo Sum; February 10th, 2014 at 05:21 PM. Reason: Fixed spelling errors.
    Strange likes this.
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

    ~ Arthur Schopenhauer, The Art of Being Right: 38 Ways to Win an Argument (1831), Stratagem XXXVIII.
    Reply With Quote  
     

  6. #5  
    Forum Ph.D. Raziell's Avatar
    Join Date
    Sep 2008
    Posts
    927
    Gonna throw another question in here. Does the heart need a connection to the brain to beat naturally? I mean... if someone got their brain ripped out by a giant death robot from the future, but the veins and everything else was left intact - not preventing bloodflow through the head - would the heart stop beating? Never quiet understood if the heart is electric or mechanic when it comes to nerves/muscles.
    A lie is a lie even if everyone believes it. The truth is the truth even if nobody believes it. - David Stevens
    Reply With Quote  
     

  7. #6  
    Moderator Moderator Cogito Ergo Sum's Avatar
    Join Date
    Jun 2013
    Location
    Belgium
    Posts
    2,519
    Quote Originally Posted by Raziell View Post
    Gonna throw another question in here. Does the heart need a connection to the brain to beat naturally? I mean... if someone got their brain ripped out by a giant death robot from the future, but the veins and everything else was left intact - not preventing bloodflow through the head - would the heart stop beating? Never quiet understood if the heart is electric or mechanic when it comes to nerves/muscles.

    Quite a far-fetched idea, but an interesting question nonetheless.

    It is known that the sympathetic and parasympathetic branches of the autonomic division of the central nervous system influence heart rate (via antagonistic control). Simply put, the lower half of the brain stem (medulla oblongata) has a control center for the heart. This control center uses neurotransmitters to increase (symp.) or decrease (parasymp.) the heart rate.

    However, heart rate is determined by the heart itself (as I have stated in a previous reply; namely via autorhythmic cells).
    A gruesome example comes from the Spanish explorers. The Maya performed ritual human sacrifices, i.e. pulling out one's heart.
    When the heart was ripped out of the rib cage, the explorers reported that the heart continued to beat! This is due to the fact the heart can contract without a connection to other parts of the body.

    Does a heart need a brain? See for yourself:
    "The heart has its own pacemaker independent of the brain. As long as it has oxygen, it continues to beat. The heart could actually be removed from the body, placed in saline solution, given oxygen, and still continue to beat. This is why although the brain is dead, the heart continues to beat."
    (cf. Brain Death | Welcome to Community Services | Life Alliance Organ Recovery Agency at Miller School of Medicine)
    Last edited by Cogito Ergo Sum; January 3rd, 2014 at 07:16 PM. Reason: "Neurotransmitters", not "proteins".
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

    ~ Arthur Schopenhauer, The Art of Being Right: 38 Ways to Win an Argument (1831), Stratagem XXXVIII.
    Reply With Quote  
     

  8. #7  
    New Member
    Join Date
    Sep 2013
    Posts
    2
    Thank you everyone for responding!
    I hope I have answered your question in a satisfying way. If not, feel free to ask more questions.
    I guess I should clarify what I mean by some of the words I used. By "heartbeat," I mean the physical feeling of a "pulse" on your chest, much like the feeling of the pulse on the wrist or on the neck, NOT the sound of the heart contraction (that I already know). I generally understand already how the heart physically contracts and how its valves closing produce the sound of the heart beat, but I'm wondering about the physical feeling ("pulse") on our chest.
    So if the atrial and ventricular contractions create the heartbeat, my question then is how? The volume of the heart is decreasing, so wouldn't we expect, if anything, that the chest would "cave in" and then "re-expand" with each heartbeat rather than "pulse" outward?
    I'm not sure why you think the heartbeat can't be attributed to the contraction of the heart muscles?
    My reasoning is this: if the heartbeat is caused by the heart contraction, and the volume of the heart decreases when the heart contracts, then if it weren't for our rib cage holding our thoracic cavity in place, wouldn't we expect our chest to kind of "cave in" and then "re-expand" with each heartbeat rather than "pulse" outward?
    It is the just vibration produced as the heart contracts and expands. It does this quite forcefully as it has to pump blood through the entire body.
    Vibration originating from where in the heart? And the vibration is that strong that we feel a "pulse" through our sternum and on our chest, despite the heart's volume decreasing on each contraction?
    Reply With Quote  
     

  9. #8  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    17,036
    Quote Originally Posted by BaneOfGodot View Post
    My reasoning is this: if the heartbeat is caused by the heart contraction, and the volume of the heart decreases when the heart contracts, then if it weren't for our rib cage holding our thoracic cavity in place, wouldn't we expect our chest to kind of "cave in" and then "re-expand" with each heartbeat rather than "pulse" outward?
    OK. I think I see what you mean. But as someone said, the beats are pretty short so its not like breathing where you can see the chest expanding and contracting with the lungs. It is just a "thump" as the heart beats. And, apparently, the noise/vibration comes mainly from the valves (*) presumably as they snap closed at the end of the cycle, rather than the contraction and expansion of the heart.

    (*) assuming the guys above know what they are talking about (I have no reason to doubt it).
    babe likes this.
    ei incumbit probatio qui dicit, non qui negat
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •