Muscle Physiology and CNS question.

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Okay, in biology we have been talking about ATP respiration, enzymes, etc.

I was reading more about the subject to find answers I have been pondering about lately, and looking on more online articles to get a better idea. I realize next semester when I take Anatomy and Physiology I'll learn all this more in-depth, but I can't wait. So, I figured what better place to ask a question than this forum.

My question has to do with the CNS and motor units. I understand that the motor units (motor nuerons and it's muscle fibers) are activated by the Nervous System through the spinal cord and the brain through the anterior horn cell, and fire/recruite accordingly depending upon the work being performed. Now, once a muscles motor units are triggered, how do the muscle and CNS actually fatigue? Would the muscle fatigue because it runs out of adenosine triphosphate, and the mitochondria cannot create more quickly enough to supply energy to the working muscle(s)? How would the CNS actually fatigue? It seem the muscle would fatigue quicker than the Nervous System because how would you beable to alternate superset in a workout? If you take a working set until muscle failure, you could immediately switch to a different muscle group and work that without a problem.

Thanks in advance!
 
Blade posted some refenences and I posted a very long paper on Peripheral Fatique (related to your muscle fatique question)and Central Fatique (CNS fatique) Here if you want to read it. Also Ron Sowers (AKA Nwlifter) wrote some interesting stuff as well.

It would be a good spot review for you. Also do a pubmed on Ca2+ (Ca++) and fatique.

Lastly, in the Muscle Growth Flowchart thread, about 9 or 10 posts down is a summary of ECC. This might help you as well.
 
Ahhhhh..... Mr DK, I knew I could count on you. ;)
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I will start reading those!
 
Haha, that link was great. That was the most insannnnnnnnnnnnnneeeeeeeeeeeeeeeeee amount of refferences I have ever come across. I have my work cut out for me. I thought I could read one quickly, but ran out of time. I have to go to my flight school, but I'll read them when I get back.

Once again, thanks!
 
DKM gave great references, but just to add to this, or rather compile this for you...

Central fatigue (ie CNS): Not really a factor if motivation is high and the contractions are not very long. (studies find central fatigue usually in very long sub max contractions, but fatigue clears and the CNS is up to par in 2-30 minutes again)

ATP: Never really exhausted, but the 'stuff' that ATP is made from can get low slowing production for replenishment. (ie glycogen, phosphates, etc)

Type of contraction: Makes a big difference.
Concentric will usually induce more of a metabolic 'backing up' of byproducts. Kinda choking the fibers
Eccentric is more of a mechanical deal. Somewhere in the exication contraction coupling we find post exercise weakness that persists even though the CNS output is high, and energy is high. Could be anywhere from the junction of the nerve to the crossbriges.

So that's it more in a 'brief undetailed' mannor. If you really want some details, "Neural Mechanics of Human Movement" by Roger Enoka will answer all your questions and much much more. :)

Ron
 
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