Fast vs. Slow Twitch Muscles


I'm getting frustrated.  I've spent the last six months trying to determine whether human fast and slow twitch muscles are innervated by nerves with separate, discrete origins as is the case with  Amphioxus Muscles .  I still rather suspect that they are, but, although I've learned a lot about muscles, I still haven't found a definitive answer, and it may be that a definitive answer doesn't yet exist.

These are the pages that I initiated during this effort: 

Muscle Innervation     
Motor Neuron Evolution
Motor Nerve Organization       
Medial Motor Column   

Amphioxus Motor Nerves    
Amphioxus Fast-Slow Twitch 
Dorsal Motor Neurons  
Ventral Motor Neurons
   Amphioxus Muscles  
  Amphioxus Locomotion    

Lamprey     Lamprey Motor Nerves     Lamprey Muscles        
Lamprey Fast-Slow Twitch   

Sharks & Rays    Shark Muscles   
Red Nucleus
Red Nucleus Cerebellum   
Teleost Muscles   
Amphibians    Amphibian Muscles   
Mammalian Muscles   

Wikipedia Extrapyramidal Revision   
Wikipedia Red Nucleus Revision     

Amphioxus Fast-Slow Twitch neurons: 

My comments and summary

The amphioxus motor neurons are divided into at least two types, dorsal compartment (DC) and ventral compartment (VC) neurons.  None of the references specify twitch speed or metabolic characteristics, but it is clear that the DC neurons are slow twitch while the VC neurons are fast twitch. 

Lamprey Fast-Slow Twitch:   

My comment
    This makes it clear that, in the lamprey, the parietal (red, slow twitch) and the central (white, fast twitch) muscle fibers are innervated by separate neuronal systems, but it doesn't describe these systems or trace them back to their origins.  Perhaps part of the problem is that the two kinds of neurons look very much alike.  However, it also says:  "Using simultaneous intracellular recordings from motoneurons and muscle fibers, Teravainen and Rovainen showed that an individual motoneuron innervates only parietal or only central muscle fibers, but not both." so perhaps these references might show the way.  

Shark Muscles   

My comment:      

    Accepting that "medial" and "anteriorcorticospinal" are equivalent, this ends my search for the separate origins of the slow and fast twitch motor neurons.  The slow twitch originate in the red nucleus and the fast twitch originate in the vestibulospinal, tectospinal and reticulospinal tracts. 

Teleost Muscles   

My comment:   

  Since, in Shark Muscles , both the "Review of the Origin ..." and Wikipedia agree that the red motor neurons are lateral, the location of the red motor neurons in teleosts is similar if, in the section on teleosts, "small motoneurons that occupy the ventral part of the motor column" means the same as "lateral".  If this is the case, then "extreme dorsal part of the motor column", in the section on teleosts, must mean the same as  "medial" and "anteriorcorticospinal".  I need to check on this.      

Amphibian Muscles   

My comments
1.  Although "Review of the Organization ..." does not draw the conclusion, it looks to me as though the primary neurons are white, fast twitch and the secondary neurons are red, slow twitch. 
2.  "Review of the Organization ..." does not discuss the origin of either the primary or the secondary neurons.     
3.  It is my memory that Brain of the Tiger Salamander did not find any evidence of a red nucleus, which Shark Muscles identified as the source of the red, slow twitch neurons.  However, when I went back and looked, I couldn't find what I remembered as Herrick's statement that he had looked for it and failed to find it.  

Mammalian Muscles   

    "The muscle fibers in mammalian axial muscles can be divided into at least 3 fiber types: slow twitch, fast twitch oxidative and glycolytic, and fast twitch glycolytic (also identified as types I, IIA, IIB by some authors).  The histochemical and physiological properties of these fiber types differ.  As the names suggest, the fast twitch glycolytic fibers are involved in strong, rapid movements involving anaerobic metabolism, while the slow twitch fibers are responsible for sustained movements and the maintenance of posture, and depend on oxidative metabolism. Some muscles are composed of a variety of fiber types; others contain only a single type*‘. All 3 fiber types generate action potentials. True non-spiking tonic fibers are found only in the eye muscles and the middle ear muscles of mammals."     

Lomo Terje - PubMed - NCBI   

Activity-dependent plasticity of transmitter release from nerve terminals in rat fast and slow muscles.
    Full length HTML available online for free. 
    "Neuromuscular junctions (NMJs) on fast and slow muscle fibers display different transmitter release characteristics that appear well adapted to the different patterns of nerve impulses that they transmit in vivo. ...
    Here, we ask whether the release properties of such NMJs, termed fast and slow, can be transformed by chronic nerve stimulation. In young adult rats, nerve impulse conduction in the sciatic nerve was blocked by TTX, and the nerve to the fast extensor digitorum longus (EDL) or the slow soleus (SOL) muscle stimulated directly below the block with slow (20 Hz for 10 sec every 30 sec) or fast (150 Hz for 1 sec every 60 sec) stimulus patterns, respectively.    
    After 3-4 weeks, originally fast EDL-NMJs and slow SOL-NMJs had become almost fully transformed to slow and fast NMJs, respectively, with respect to maintenance of transmitter release during tonic 20 Hz stimulation in vitro and ratio of quantal content to vesicle pool size. ...
    We conclude that fast and slow NMJs display marked plasticity by being able to adapt important release characteristics to the impulse patterns imposed on them."   
My comments
    1.  This implies that muscle type, fast or slow, is determined by the input from the motor neuron rather than  being an intrinsic characteristic of the muscle fiber. 
    2.  A further implication is that I can identify the type, fast or slow, of the receiving muscle fiber by the speed of the motor neuron. 
The present results show that chronic nerve stimulation with appropriate stimulus patterns can transform fast and slow NMJs into slow and fast NMJs, respectively."          
Moreover, the transformations appear analogous to the transformations of contractile properties of fast and slow muscle fibers induced by cross-reinnervation (Close, 1969) or appropriate activation of fast and slow muscles by electrical nerve (Salmons and Vrbova, 1969) or muscle (Lømo et al., 1974; Eken and Gundersen, 1988; Windisch et al., 1998) stimulation. "  

Electrical muscle activity pattern and transcriptional and posttranscriptional mechanisms regulate PKA subunit expression in rat skeletal muscle.