Motor Nerve Organization

Cross references:   Muscle Innervation      Motor Neuron Evolution     
Mammalian Muscles    Perinatal Behavior    
Motor Programs 
    Excitation vs. Inhibition        

The PDF cited below is 37 pages long and discusses the motoneurons of 8 different animals.   
A review of the organization and evolution of motoneurons
innervating the axial musculature of vertebrates (Goog) - 1986    Full length PDF available online for free.  
This is a list of the pages referencing the above article as of 10-13-13.  In order to avoid duplication, I'll limit what I quote on each of the pages to just what is specific to that topic. 

Motor Neuron Evolution

Amphioxus Muscles

 Amphioxus Motor Nerves

Lamprey Muscles  

Lamprey Fast-Slow Twitch

Medial Motor Column
Shark Muscles

Teleost Muscles Amphibian Muscles Mammalian Muscles Somatic Nervous System


The Local Circuit Neurons

The most explicit reference I've found so far for the preceding blog entry is in: 
    Neuroscience, third edition, page 371   
    ed. Dale Purves, et al. 
    Sinauer Associates, Publishers 

"The neural circuits responsible for the control of movement can be divided into four distinct but highly interactive subsystems, each of which makes a unique contribution to motor control.  The first of these subsystems is the local circuitry within the gray matter of the spinal cord and the analogous circuitry in the brain stem.  The relevant cells include the lower motor neurons (which send their axons out of the brainstem and spinal cord to innervate the skeletal muscles of the head and body, respectively) and the local circuit neurons (which are the major source of synaptic input to the lower motor neurons)." 


I spent some time "reading about the innervation of motor neurons", not in our subcortical ancestors, but in we humans.  Paraphrasing Medial Motor Column , it turns out that the rubrospinal tract, the vestibulospinal tract, the tectospinal tract and the reticulospinal tract   influence the output from the Alpha motor neurons , not by providing input to the Alpha motor neurons directly, but by providing input to the very numerous Interneurons which then influence the output from the  Alpha motor neurons .    

180701 - 1730