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Fig. 670. Diagram showing afferent (sensory) and efferent fibers

Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fasciculi.


Structure of the Gray Substance.—The gray substance consists of numerous nerve cells and nerve fibers held together by neuroglia. Throughout the greater part of the gray substance the neuroglia presents the appearance of a sponge-like network, but around the central canal and on the apices of the posterior columns it consists of the gelatinous substance already referred to. The nerve cells are multipolar, and vary greatly in size and shape. They consist of (1) motor cells of large size, which are situated in the anterior horn, and are especially numerous in the cervical and lumbar enlargements; the axons of most of these cells pass out to form the anterior nerve roots, but before leaving the white substance they frequently give off collaterals, which reënter and ramify in the gray substance. 113 (2) Cells of small or medium size, whose axons pass into the white matter, where some pursue an ascending, and others a descending course, but most of them divide in a T-shape manner into descending and ascending processes. They give off collaterals which enter and ramify in the gray substance, and the terminations of the axons behave in a similar manner. The lengths of these axons vary greatly: some are short and pass only between adjoining spinal segments, while others are longer and connect more distant segments. These cells and their processes constitute a series of association or intersegmental neurons (Fig. 668), which link together the different parts of the medulla spinalis. The axons of most of these cells are confined to that side of the medulla spinalis in which the nerve cells are situated, but some cross to the opposite side through the anterior commissure, and are termed crossed commissural fibers. Some of these latter end directly in the gray substance, while others enter the white substance, and ascend or descend in it for varying distances, before finally terminating in the gray substance. (3) Cells of the type II of Golgi, limited for the most part to the posterior column, are found also in the substantia gelatinosa of Rolando; their axons are short and entirely confined to the gray substance, in which they break up into numerous fine filaments. Most of the nerve cells are arranged in longitudinal columns, and appear as groups on transverse section (Figs. 669, 670, 671).



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Reference

Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.


Cite this page: Hill, M.A. (2024, April 22) Embryology Gray0670.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Gray0670.jpg

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current12:58, 17 October 2012Thumbnail for version as of 12:58, 17 October 2012800 × 504 (67 KB)Z8600021 (talk | contribs) ==Fig. 670. Diagram showing afferent (sensory) and efferent fibers== Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fascicu