Symposium on the Role of the Vestibular Organs in Space Exploration (1970) / Chapter Skim
Currently Skimming:
ANATOMICAL ASPECTS ON THE FUNCTIONAL ORGANIZATION OF THE VESTIBULOSPINAL PROJECTION, WITH SEPCIAL REFERENCE TO THE SITES OF TERMINATION
ANATOMICAL ASPECTS ON THE FUNCTIONAL ORGANIZATION OF THE VESTIBULOSPINAL PROJECTION, WITH SEPCIAL REFERENCE TO THE SITES OF TERMINATION
Pages 167-182
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 167... ...
The spinal projection from the vestibular nuclei can be separated into two different fiber systems: the classical vestibulospinal tract and the fibers descending in the medial longitudinal fasciculus. Because of their origin from the medial vestibular nucleus and their medial course in the brainstem and the spinal cord, the latter is called the medial vestibulospinal tract, and the more laterally coursing classical vestibulospinal fibers is called the lateral vestibulospinal tract.
|
From page 168... ...
THE VESTIBULOSPINAL PROJECTION The fiber connections from the vestibular nuclei to the spinal cord can be separated into two different fiber systems: the classical vestibulospinal tract and the fibers descending in the medial longitudinal fasciculus. These two pathways should be called the lateral and the medial vestibulospinal tract, respectively, as proposed by Nyberg-Hansen (ref.
|
From page 169... ...
9) that the lateral vestibulospinal tract takes its origin solely from the lateral vestibular nucleus.
|
From page 170... ...
practical importance in physiological studies of the lateral vestibulospinal tract. As will be further commented upon in the section on the medial vestibulospinal tract, it follows from this arrangement that the only conclusive way to identify fibers from the vestibular nuclei descending in the medial longitudinal fasciculus in the spinal cord is to observe them in the area allotted to the fascicle in the cervical cord.
|
From page 171... ...
of a nerve cell in lamina VIII in a case with a lesion of the medial vestibular nucleus involving the origin of the medial vestibulospinal tract. (From refs.
|
From page 172... ...
in spinal extensor motoneurons following stimulation of the lateral vestibular nucleus, indeed indicates that this really may be the case. However, in accordance with the anatomical observations outlined above, physiological studies as well leave no doubt that a large number, if not the majority of lateral vestibulospinal tract fibers terminate on interneurons in laminae VII and VIII, and not directly on motoneurons (ref.
|
From page 173... ...
. The number of medial vestibulospinal fibers is very modest when compared with those in the lateral vestibulospinal tract, which is the major pathway from the vestibular nuclei to the spinal cord, as recently confirmed physiologically by Wilson, Wylie, and Marco (ref.
|
From page 174... ...
The area of termination is much less extensive than is that of the lateral vestibulospinal tract. FUNCTIONAL CONSIDERATIONS The lateral vestibular nucleus and the lateral vestibulospinal tract are known to exert a tonic facilitatory influence on postural tonus and spinal extensor mechanisms (for references, see ref.
|
From page 175... ...
-- Diagram of a transverse section of the spinal cord showing the location in the ventrolateral funiculus and the sites of termination within the spinal gray matter of pontinr reticulospinal and lateral vestibulospinal fibers. Note the similarities between the two pathways with regard to the course and sites of termination, (l-'rom ref.
|
From page 176... ...
There appears thus to be a satisfactory anatomical substratum for the physiologically demonstrated monosynaptical activation. Because of its restriction to the upper half of the spinal cord, and its origin from the medial vestibular nucleus, the medial vestibulospinal tract is generally assumed to be concerned with the adjustments of the tonus in the muscles of the head and neck and with movements of the head occurring simultaneously with conjugate deviation of the eyes, particularly in the horizontal plane (see refs.
|
From page 177... ...
However, recent physiological studies indicate that the medial and descending vestibular nucleus by way of the medial vestibulospinal tract exert a presynaptic inhibition of primary afferents in the spinal cord, and that this is the likely basis for the phasic inhibition of spinal reflexes occurring during REM sleep.
|
From page 178... ...
PETRAS, J M.: Cortical, Tectal and Tegmental Fiber Connections in the Spinal Cord of the Cat.
|
From page 179... ...
M.; AND MARCO, L A.: Projection to the Spinal Cord From the Medial and Descending Vestibular Nuclei of the Cat.
|
From page 180... ...
Pompeiano: I should like to mention the results of some unpublished experiments made recently by Cook, Cangiano, and myself, indicating that the effects of Vestibular nerve stimulation on the primary afferents in the lumbar cord are not mediated by the medial vestibulospinal tract nor by propriospinal descending pathways, but are transmitted to the spinal cord by collaterals from the vestibular nuclei to brainstem structures whose descending pathways course along the ventral quadrants. The problem of the distribution of (he vestibulospinal synapses within the somatodendritic complex of the extensor and Abnormal Motor Activities.
|
From page 181... ...
Do you still think all the cells project to the spinal cord or would you consider there might be interneurons in there also? Nyberg-Hansen: I have not personally done retrograde studies on this, but from the studies of Pompeianoand Brodal, it appears like all large, medium-sized cells and small neurons of the lateral nucleus project to the cord.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.