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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
some cell types is termed the cone of origin. These granules disappear (chromatolysis) during fatigue or after prolonged stimulation of the nerve fibers connected with the cells. They are supposed to represent a store of nervous energy, and in various mental diseases are deficient or absent. The nucleus is, as a rule, a large, well-defined, spherical body, often presenting an intranuclear network, and containing a well-marked nucleolus.


FIG. 627– Pyramidal cell from the cerebral cortex of a mouse. (After Ramón y Cajal.) (See enlarged image)



FIG. 628– Cell of Purkinje from the cerebellum. Golgi method. (Cajal.) a. Axon. b. Collateral. c and d. Dendrons. (See enlarged image)

  In addition to the protoplasmic network described above, each nerve cell may be shown to have delicate neurofibrils running through its substance (Fig. 629); these fibrils are continuous with the fibrils of the axon, and are believed to convey nerve impulses. Golgi has also described an extracellular network, which is probably a supporting structure.

Nerve Fibers.—Nerve fibers are found universally in the peripheral nerves and in the white substance of the brain and medulla spinalis. They are of two kinds—viz., medullated or white fibers, and non-medullated or gray fibers.
  The medullated fibers form the white part of the brain and medulla spinalis, and also the greater part of every cranial and spinal nerve, and give to these structures

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