Red Nucleus

Cross references:     Wikipedia Red Nucleus Revision     
Red Nucleus Evolution   
Red Nucleus Cerebellum    
Red Nucleus Iron   
Heme      Globin     Myoglobin     
Myoglobin Evolution   
Fast vs. Slow Twitch Muscles   


My motivation for spending so much time on the  Fast vs. Slow Twitch Muscles dichotomy is what I perceive to be the similarity between this dichotomy and the dichotomy of  Human Asymmetry  .  Although I haven't really established with certainty that the neurons which innervate red, slow twitch muscles originate in the red nucleus, I'm going to assume for the moment that they do and look for asymmetric input to the red nucleus from both the nervous and the endocrine system.     

Searching Google for "red nucleus" yields 17,900,000 claimed references. 

Red nucleus (Wiki)   
    "The red nucleus is a structure in the rostral midbrain involved in motor coordination."  

Cn3nucleus.pngTransverse section through the midbrain showing the location of the red nuclei. The superior colliculi are at the top of image and the cerebral peduncles at the bottom of image – both in section.

It is pale pink in color; the color is believed to be due to iron, which is present in the red nucleus in at least two different forms; hemoglobin and ferritin. [1] It comprises a caudal magnocellular and a rostral parvocellular part. It is located in the tegmentum of the midbrain next to the substantia nigra. The red nucleus and substantia nigra are subcortical centers of the extrapyramidal motor system.

Red Nucleus (the "Ruber")  (Goog)  
    " It appears to have a high iron content and is more vascular than the surrounding tissue, and in some brains is pinkish."  
Inputs to the ruber arise from motor areas of the brain and in particular the deep cerebellar nuclei (via superior cerebellar peduncle; crossed projection) ..."

Functional and anatomic differentiation between parvicellular and magnocellular regions of red nucleus in the monkey. - 1986  (PubMed)   
    "Of the units in the RNm 98.5% discharged in high frequency bursts during movement. Only 52% showed reliable responses to somatosensory stimulation, and the responses observed were weaker than the movement-related discharge. None of the units recorded in the RNp showed strong movement-related discharge, and 51% were completely unresponsive during both motor and sensory tests."  
Anterograde transport of WGA-HRP from the motor cortex demonstrated dense terminal label in RNp as contrasted with light label in RNm. Retrograde transport of WGA-HRP from RNm labeled many more cells in the cerebellar interpositus nucleus than in motor cortex. We concluded that input to RNm from the cerebellum is the likely source of the strong movement-related activity recorded from cells in the RNm. The absence of appreciable movement-related activity in parvicellular red nucleus provides a clear functional distinction between this division and the magnocellular division of the red nucleus."  

Behavioural Brain Research | Vol 28, Isss 1–2, Pgs 1-244, (April–May, 1988)
    This entire issue of this journal is focused on the red nucleus.  It is comprised of 36 different articles.  I've scanned through the titles very quickly without finding anything that explicitly specifies the innervation of the red muscle.  I'll now go back through them more slowly looking for hints.  I'm not sure I'll find any.   

Projections from the red nucleus and surrounding areas to the brainstem and spinal cord in the cat. An HRP and autoradiographical tracing study. 
Regarding the RN projections to the spinal cord, the autoradiographical tracing results revealed somatotopically organized contralateral RN projections to laminae V, VI and VII."  
My comment:   
    So maybe I need to look at laminae V, VI and VII.  

Target cells of rubrospinal tract fibres within the lumbar spinal cord 
This short review concerns the problem of how the red nucleus contributes to the initiation and execution of movements. However, it deals with only one aspect of this problem, and focusses on the question of which intrinsic spinal interneuronal networks are used by neurones in the red nucleus to induce movements. The evidence is reviewed that neurones in the red nucleus have access to interneurones with a great variety of functions, excitatory as well as inhibitory. These interneurones are interposed in a number of different spinal reflex pathways, and include both the first and last order interneurones of these pathways. Through them different sets of motoneurones may be affected. All types of interneurones involved are also used by other descending systems, e.g. by cortico- and/or reticulospinal systems, and integrate descending commands with information from various peripheral receptors."  
My comments:   
1.  Perhaps I need to look more closely at spinal interneurones and motor neurons. 
2.  Related citations at:

The Red Nucleus: Past, Present, and Future - 2000 (Goog) 
Full length PDF available online for free.    
     "The red nucleus (RN) can be divided into two histologically distinct structures: the parvocellular red nucleus (RNp) and the magnocellular red nucleus (RNm). ... Research has shown that RNm and its primary efferent pathway, the rubrospinal tract, comprise most of the red nuclei related structures from early vertebrates through the mammals."
Studies of the mammalian red nucleus demonstrate
that larger cells are found in RNm, whereas medium and small cells are typically found in RNp "  
tracts are also absent in boid snakes and sharks who use axial movements for locomotion rather than limbs [9]."  
     "Expansion of the pyramidal tract in primates has paralleled the regression of RNm [3]. One study has shown that axons from both the rubrospinal and pyramidal tracts end on the same segmental interneurons and propriospinal neurons [10]"
     "Haines [12] indicates that relatively few rubrospinal axons have been shown to extend below the cervical enlargement of the human spinal cord. Clinical findings
indicate that the human rubrospinal system exerts its control mainly over the upper extremity and has little influence over the lower extremity. The data strengthen the argument that RNm and its corresponding rubrospinal tract, with increasing dominance of the pyramidal tract, have shrunk to influence upper limb control only. ...

    It is clear that projections to and from the RNm have changed from early vertebrates through primates. While RNm influences all limb movements in lower vertebrates,
it appears delegated to upper limb control in primates.
"In mammals, such as the North American possum, data showed two cerebellar nuclei projecting contralaterally to the RN: the interposed nucleus to its magnocellular part and the lateral (dentate) nucleus to its parvocellular part." 
     "The RN of early vertebrates is a functionally and anatomically different structure than that of the human RN. RNm of lower vertebrates is part of a dominant motor pathway controlling movement of limbs.  Anatomically, RNm is the prevailing portion of the RN in these creatures. The telencephalization process and the development of the neocerebellum in primates has brought about a higher level of motor circuitry, possibly  causing the pyramidal tract to flourish and the RN to reorganize." 
"RNm appears to be a backup to the corticospinal tract, with both pathways sharing synapse locations in the spinal cord."  
My comments:     
    1.  "
RNm and its primary efferent pathway".  It is my observation that neurons which project a considerable distance, i.e. to targets beyond the same nucleus, are large (magnocellular) while neurons which project only a very short distance, i.e. to targets within the same nucleus are small (parvocellular). 
In mammals, such as the North American possum, data showed two cerebellar nuclei projecting contralaterally to the RN: the interposed nucleus to its magnocellular part and the lateral (dentate) nucleus to its parvocellular part."   
    2.  "
Rubrospinal tracts are also absent in boid snakes and sharks"  This contradicts Shark Muscles .   
    3.  "
One study has shown that axons from both the rubrospinal and pyramidal tracts end on the same segmental interneurons and propriospinal neurons [10]"  I need to find out where these "same segmental interneurons and propriospinal neurons" project.  This may provide a solid connection between the red nucleus and the red muscles.         

Demonstration of the Medullary Lamellae of the Human Red Nucleus with High-resolution Gradient-echo MR Imaging - 2000 (Goog)   
    "Human red nuclei are a pair of globular structures located in the midbrain and can be divided into the caudally located magnocellular and rostrally located parvicellular subnuclei (3).  
    From comparative neuroanatomic studies, it is known that the former is strongly developed in lower mammals, becomes less predominant among the apes, and in humans is only rudimentary. Indeed, there are only a few magnocellular neurons in the human red nucleus (1). They are gathered largely into two categories, the dorsomedial and the ventral groups, with an occasional single neuron scattered among the fibers of the superior cerebellar peduncle (1).  
    On the other hand, the parvicellular subnucleus of the red nucleus is less developed in lower mammals, more pronounced among the apes, and finds its highest development in humans. It forms the bulk of the human red nucleus and can be subdivided histologically by two medullary lamellae into three parts: the pars oralis, the pars dorsomedialis, and the pars caudalis (1, 3, 4).

The red nucleus and the rubrospinal projection in the mouse.