Mammalian Muscles

Cross references:    Motor Neuron Evolution      Muscle Innervation        
Amphioxus Motor Nerves     Amphioxus Muscles  Lamprey Muscles  
Shark Muscles    Teleost Muscles  
Amphibian Muscles     
Medial Motor Column    Human Muscles 

A review of the organization and evolution of motoneurons innervating the axial musculature of vertebrates. (Goog) - 1987   
See:  Motor Nerve Organization
    Abstract
    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. 
    The motoneurons innervating different muscle fiber types are generally not segregated from one another in the motor columns.   
   
All 3 fiber types generate action potentials.  Tonic fibers are retained in some muscles of reptiles and birds, but are absent in axial muscles of mammals.   



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From:  Searching PubMed for "retrograde tracing motor neuron" ... 
    See: 
Muscle Innervation
Morphology of motoneurons in a mixed motor pool of the cat facial nucleus that innervate orbicularis oculis and quadratus labii superioris, stained intracellularly with horseradish peroxidase. - 1985  (PubMed)      
My comment
    Although there is no distinction between red and white muscles, this article is of interest because it was the first to report retrograde tracing from muscles and motor neurons to the source of the motor neurons. 
    There were 5 related citations and 3 Cited by ... 's, but none of them mentioned either red or white muscles. 

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From:  Searching PubMed for "retrograde tracing motor neuron" ... 
    See: 
Muscle Innervation

Horizontal eye movement networks in primates as revealed by retrograde transneuronal transfer of rabies virus: differences in monosynaptic input to "slow" and "fast" abducens motoneurons. - 2006  (PubMed)      
    "The sources of monosynaptic input to "fast" and "slow" abducens motoneurons (MNs) were revealed in primates by retrograde transneuronal tracing with rabies virus after injection either into the distal or central portions of the lateral rectus (LR) muscle, containing, respectively, "en grappe" endplates innervating slow muscle fibers or "en plaque" motor endplates innervating fast fibers."  
    "
Premotor connectivity of slow MNs, revealed here for the first time, involves mainly the supraoculomotor area, central mesencephalic reticular formation, and portions of medial vestibular and prepositus hypoglossi nuclei carrying eye position and smooth pursuit signals. Results suggest that slow MNs are involved exclusively in slow eye movements (vergence and possibly smooth pursuit), muscle length stabilization and gaze holding (fixation), and rule out their participation in fast eye movements (saccades, vestibulo-ocular reflex).  
    By contrast, all known monosynaptic pathways to LR MNs innervate fast MNs, showing their participation in the entire horizontal eye movements repertoire."  
    "
The different connectivity of fast and slow MNs parallel differences in properties of muscle fibers that they innervate, suggesting that muscle fibers properties, rather than being self-determined, are the result of differences of their premotor innervation."  
My comments
1.  This abstract does not give any examples of "monosynaptic pathways to LR MNs", so it's difficult to contrast them with the "Premotor connectivity of slow MNs".      
2.  There was a single "Related citation" which seemed promising:

Related citation:        See:  Muscle Innervation   
Motoneurons of twitch and nontwitch extraocular muscle fibers in the abducens, trochlear, and oculomotor nuclei of monkeys.  
    "Eye muscle fibers can be divided into two categories: nontwitch, multiply innervated muscle fibers (MIFs), and twitch, singly innervated muscle fibers (SIFs). We investigated the location of motoneurons supplying SIFs and MIFs in the six extraocular muscles of monkeys. 
    Injections of retrograde tracers into eye muscles were placed either
    centrally, within the central SIF endplate zone; 
    in an intermediate zone, outside the SIF endplate zone, targeting MIF endplates along the length of muscle fiber;  
    or distally, into the myotendinous junction containing palisade endings.  
    Central injections labeled large motoneurons within the abducens, trochlear or oculomotor nucleus, and smaller motoneurons lying mainly around the periphery of the motor nuclei.  
    Intermediate injections labeled some large motoneurons within the motor nuclei but also labeled many peripheral motoneurons.  
    Distal injections labeled small and medium-large peripheral neurons strongly and almost exclusively.  
    The peripheral neurons labeled from the lateral rectus muscle surround the medial half of the abducens nucleus:  
    from superior oblique, they form a cap over the dorsal trochlear nucleus;  
     from inferior oblique and superior rectus, they are scattered bilaterally around the midline, between the oculomotor nucleus;  
    from both medial and inferior rectus, they lie mainly in the C-group, on the dorsomedial border of oculomotor nucleus.  
    In the medial rectus distal injections, a "C-group extension" extended up to the Edinger-Westphal nucleus and labeled dendrites within the supraoculomotor area.  
    We conclude that large motoneurons within the motor nuclei innervate twitch fibers, whereas smaller motoneurons around the periphery innervate nontwitch, MIF fibers. The peripheral subgroups also contain medium-large neurons which may be associated with the palisade endings of global MIFs. The role of MIFs in eye movements is unclear, but the concept of a final common pathway must now be reconsidered."  
My comments on this comment
1.  The MIF (non-twitch, slow, presumably red) fibers are innervated from such a widely dispersed population of neurons that it's not easy to see them as being innervated from a single source such as the ventral compartment neurons of the Amphioxus (See: Amphioxus Motor Nerves ).  Of course, one explanation might be that they have evolved from ventral compartment neurons.    
2.  There were both interesting Related citations and interesting Cited by's linked to this comment, and both these Related citations and Cited by's had further Related citations and Cited by's that were interesting
.


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From:  Searching PubMed for "retrograde tracing motor neuron" ... 
    See: 
Muscle Innervation
Characterization of last-order premotor interneurons by transneuronal tracing with rabies virus in the neonatal mouse spinal cord. - 2011 (PubMed)      
    "Glycinergic neurons connected to (triceps surae [TS] muscles) motoneurons (MNs)s represented 50% of (last-order interneurons [loINs])s ipsilaterally and 10% contralaterally."  


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From:  Searching PubMed for "retrograde tracing motor neuron" ... 
    See: 
Muscle Innervation   

The red nucleus and the rubrospinal projection in the mouse.   
    See:   Red Nucleus







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