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  #1  
Old 08-06-2014
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Default cant understand Length-tension curve

Length-tension curve I can't understand this is it high yield
It is section 3 ch 2 in kaplan physio 2012
The whole chapter is difficult
Anyone could help ?
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Old 08-06-2014
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Alright I will start from the very basics. There are many myofibrils that are found in a muscle fiber (aka muscle cell). Each myofibrils contain many sarcomeres. These sarcomeres run from Z line to Z line. The actin filaments (thin filaments) are attached to the Z line and the myosin (thick filaments) are attached to the M line. Now to answer your question, the tension created depends on the degree of cross-linkage between thin and thick filaments. So the greater the cross-linkage between actin and myosin molecules the greater the tension created. I will give you an analogy: If you don't stretch a rubber band there is no elastic recoil, but if you stretch it, there is elastic recoil. The magnitude of elastic recoil depends on the degree of stretch, intuitively the more you stretch the rubber band the greater the elastic recoil that is created, but if your overstretch it then there is no elastic recoil. Like wise overstretching of the muscle means means no cross-linkage between actin and myosin, so no tension created.

Check the image posted. If you check the image, you will note that the part labelled A does not create that much tension because the thin filaments are overlapping each other!


Also search for "Sarcomere length-tension relationship" video on Youtube, it's about 9 mins long.

I hope you understand, if not I will try to clarify even more. Good luck!
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  #3  
Old 08-06-2014
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Thank you very much
I begin to understand but Im confused about terms like
Preload afterload active &passive&total tension I read in many references but didnot make sense to me
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Old 08-06-2014
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The heart muscle is pre-streched to certain length at resting stage and this is called the preload. If more blood enters the heart, it stretches the heart muscle and increases the preload. For example, when the venous return increases the preload increases. This increase in preload results in an increase in the elastic stretch of the heart muscles and according to Frank-Starling's law, the strength of the contraction will increase too leading to an increase in the stroke volume (the amount of blood pumped by the heart per beat).

Now the passive tension refers to the elastic force which increases when the blood fills up the ventricle, and the active tension being the kinetic force generated. So the elastic force (passive tension) is converted to kinetic energy (active tension) which results in an increase in stroke volume.

The afterload is the resistance the heart "faces" when pumping the blood. When the total peripheral resistance increases the heart will therefore have to pump the blood against a greater force i.e. the afterload.

Hope it helps!

Last edited by eizou; 08-06-2014 at 02:41 PM.
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Old 08-07-2014
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Got it
Could u elaborate those, why are they for?
-inward rectifier k channel
Funny current
Sorry for bothering you
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Old 08-07-2014
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You want to check this website to answer your question regarding inward rectifier potassium channel:
http://www.prep4usmle.com/forum/thread/99783/

And this website regarding funny current:
http://www.usmleforum.com/files/forum/2011/1/582661.php

I hope it helps! If you got any questions, feel free to ask, that's what this website is for. Good luck
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Old 08-08-2014
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Got it many thanks to u
I really appreciate ur response
God bless you
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Old 08-21-2014
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Quote:
Originally Posted by eizou View Post
Alright I will start from the very basics. There are many myofibrils that are found in a muscle fiber (aka muscle cell). Each myofibrils contain many sarcomeres. These sarcomeres run from Z line to Z line. The actin filaments (thin filaments) are attached to the Z line and the myosin (thick filaments) are attached to the M line. Now to answer your question, the tension created depends on the degree of cross-linkage between thin and thick filaments. So the greater the cross-linkage between actin and myosin molecules the greater the tension created. I will give you an analogy: If you don't stretch a rubber band there is no elastic recoil, but if you stretch it, there is elastic recoil. The magnitude of elastic recoil depends on the degree of stretch, intuitively the more you stretch the rubber band the greater the elastic recoil that is created, but if your overstretch it then there is no elastic recoil. Like wise overstretching of the muscle means means no cross-linkage between actin and myosin, so no tension created.

Check the image posted. If you check the image, you will note that the part labelled A does not create that much tension because the thin filaments are overlapping each other!


Also search for "Sarcomere length-tension relationship" video on Youtube, it's about 9 mins long.

I hope you understand, if not I will try to clarify even more. Good luck!
Awesome explanation. That graph you posted make a lot sense now
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