Intrafusal muscle fibers vs Golgi Tendon Organs

[ChessMaster3000]

I was wondering if somebody could clarify a couple of issues related to these, as I couldn't find great consistent info online. Many thanks in advance!

First, how useful is this information? I only ever came across one UW question on it, but it seems like it would/should be a high yield topic as there is a lot of physiology happening.

Second, are "Muscle spindles" equivalent to intrafusal muscle fibers? Are intrafusal fibers the ones responsible for causing relaxation of the antagonist muscles? If so, is the function of the GTO only to prevent over contraction of the muscle in whose tendon it resides? Finally, I know that intrafusal fibers are innervated by gamma motor neurons to reset them during a muscle contraction. Is there any similar motor innervation of GTO or does it just relay afferent information to (i presume) the inhibitor neurons of the spinal cord that synapse on the alpha motor neurons of that same muscle?

Thanks again!!

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[targ489]

The intrafusal is the spindle; it's just designated intra vs extra (normal muscle). It's used for proprioception. Basically you have the bag fibers at the center of the spindle with an afferent 1a that detect rate and amount of change in the muscle. Then you have the straight fibers toward the end of the spindle which can detect amount of change via an afferent 2. The bag fibers are dynamic allowing it to change through readjusting themselves and adapting mechanically, whereas the straight only detect THAT we are changing. The whole point of the spindle is to detect youre muscle is being stretched. So that's where the gamma efferent comes in, to keep the spindle taught upon extrafusal muscle contraction, alpha and gamma fire together. The GTO is at the tendon and is like you said to prevent the muscle from snapping. It's a weight detector, like in a supermarket for weighing fruits, when it gets too tight, it fires the inverse myotatic reflex, relaxing the muscle

 

[ChessMaster3000]

The intrafusal is the spindle; it's just designated intra vs extra (normal muscle). It's used for proprioception. Basically you have the bag fibers at the center of the spindle with an afferent 1a that detect rate and amount of change in the muscle. Then you have the straight fibers toward the end of the spindle which can detect amount of change via an afferent 2. The bag fibers are dynamic allowing it to change through readjusting themselves and adapting mechanically, whereas the straight only detect THAT we are changing. The whole point of the spindle is to detect youre muscle is being stretched. So that's where the gamma efferent comes in, to keep the spindle taught upon extrafusal muscle contraction, alpha and gamma fire together. The GTO is at the tendon and is like you said to prevent the muscle from snapping. It's a weight detector, like in a supermarket for weighing fruits, when it gets too tight, it fires the inverse myotatic reflex, relaxing the muscle

I just did a little reading and it appears the inverse myotatic reflex is simply the GTO inhibiting the alpha motoneurons to the same muscle. I do remember learning that some sort of reflex activates the antagonist muscles--do you know if that is the GTO or the stretch (spindle) reflex? I can't seem to find it, or perhaps both of these reflexes do a little bit of antagonist muscle activation.

 

[targ489]

I just did a little reading and it appears the inverse myotatic reflex is simply the GTO inhibiting the alpha motoneurons to the same muscle. I do remember learning that some sort of reflex activates the antagonist muscles--do you know if that is the GTO or the stretch (spindle) reflex? I can't seem to find it, or perhaps both of these reflexes do a little bit of antagonist muscle activation.

From my understanding, when the GTO is activated it goes back to the spinal cord and antagonizes the muscle being overstretched and also activates the antagonist through an interneuron.

http://users.atw.hu/blp6/BLP6/HTML/common/M9780323045827-009-f007.jpg

 

[alicealicealice]

Does anyone know a good source to learn this kind of muscle stuff? I don't have tons of time but I literally never learned it the first time; there's nothing in FA but I would like to get an idea of what the need to know information is and get the basic concept down. No matter what combination of things I googled, if it has the "muscle" in it the first 100 hits are worthless fitness crap.

 

[ChessMaster3000]

Does anyone know a good source to learn this kind of muscle stuff? I don't have tons of time but I literally never learned it the first time; there's nothing in FA but I would like to get an idea of what the need to know information is and get the basic concept down. No matter what combination of things I googled, if it has the "muscle" in it the first 100 hits are worthless fitness crap.

It's hard to find info on this for sure. Actually, I think if you wiki the terms intrafusal muscle fiber, muslce spindle, golgi tendor, alpha motoneurons (the "normal" ones), gamma motoneurons, and finally 1a, 1b, and II afferents, you will have understood everything. the wiki pages on these topics are solid and are more than enough. I should just mention that this entire topic itself is low yield, but it can show up, so dont feel the need to go too deep into it. If you can understand what all of those terms mean, that's 260+ level right there.

 

[Transposony]

Does anyone know a good source to learn this kind of muscle stuff? I don't have tons of time but I literally never learned it the first time; there's nothing in FA but I would like to get an idea of what the need to know information is and get the basic concept down. No matter what combination of things I googled, if it has the "muscle" in it the first 100 hits are worthless fitness crap.

What I have found if you search the term under images it not only gets you some cool images but if you click on those images they usually take you to some educational site like a university or a specialty website.
For example, I searched for the terms "intrafusal muscle fiber" under images and got this: https://www.google.com/search?q=intrafusal muscle fiber&espv=210&es_sm=93&source=lnms&tbm=isch&sa=X&ei=M0b-UtabG8e_0gHJnYC4AQ&ved=0CAkQ_AUoAQ&biw=1378&bih=839&dpr=1

And when I clinked on one of the images I got this: http://michaeldmann.net/mann4b.html

 

[alicealicealice]

Thanks

 

[sanj238]

the best source I can think of is Kaplan Neuroanatomy. It concisely explains all of the stretch reflexes in one page.

 

[alicealicealice]

Thanks, I would but I didnt have that. I went to constanzo and it was good enough I think

 

[W19]

I am glad this topic is low yield. I have read that stuff countless times as a MS1, and still get confused about it...

 

[worldbeater]

The classic example they will use about GTO is an olympic weightlifter who does his (or her) lift, raises it, and then lets the weight fall as opposed to putting the weight back down. Their GTO is firing at the peak of the lift, hence the reason for dropping the weight.