Lamprey Fast-Slow Twitch

Cross references:   Fast vs. Slow Twitch Muscles   
Lamprey     Lamprey Motor Nerves     Lamprey Muscles        

A review of the organization and evolution of motoneurons
innervating the axial musculature of vertebrates (Goog) - 1986 
Full length PDF available online for free.     

    From: Lamprey Muscles  

    "The central fibers are relatively large, they generate spikes following stimulation of peripheral nerves, and they have the ultrastructure and histochemistry typical of fast, white muscle fibers.
    The smaller parietal fibers are non-spiking, and have the ultrastructural and histochemical characteristics of slow, red muscle."  
My comment
    This paper does not actually specify the colors of the muscle fibers.  It labels the fibers as either "parietal" or "central" and then distinguishes between them on the basis of ultrastructure, histochemistry and whether or not they spike.  Since the parietal fibers are not described as being actually "red", it may be that they do not contain Myoglobin .       
    This paper does make it clear that the parietal (slow twitch) and the central (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, suggesting that, like the muscle fibers, neither of the neurons are red. 


Activities of identified interneurons, motoneurons, and muscle fibers during fictive swimming in the lamprey and effects of reticulospinal and dorsal cell stimulation.  
    "Almost all slow muscle fibers exhibited excitatory junctional potentials (EJPs) during swimming activity. The number of EJPs per cycle increased with the intensity of ventral root (VR) bursting. Few twitch fibers were active, and these fired action potentials only during high intensities of VR bursts." 
My comment
    See:   Lamprey Locomotion .    


Primary afferents evoke excitatory amino acid receptor-mediated EPSPs that are modulated by presynaptic GABAB receptors in lamprey.  
The primary afferent neurons (dorsal cells) are of two types in lamprey, which are fast (touch) and slowly adapting (pressure), respectively."  
My comments:        
    The distinction between "fast (touch) and slowly adapting (pressure)" primary afferent neurons echos the distinction between fast twitch and slow twitch muscles.  Is this just a coincidence, or do fast primary afferent neurons contact fast twitch muscles and slow primary afferent neurons contact slow twitch muscles?   

    From:  GABA/Glycine Inhibition .     
My comment
    Although the title mentions dorsal and ventral myotomes, the text does not draw a clear distinction between the two.  I did not find any way to compare the results of this paper with 
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