. Anatomy, descriptive and applied. Anatomy. THE SPINAL CORD AND BRAIN 811 branches soon after its tlqwrture from the cell; such axoncs ai\- called dendraxones. The axones and their collaterals end in terminal arborizations, tlu' telodendria. The axone is the distriljulive or emissive (cellulifugal) conductor of nerve im|)ulses. There is, therefore, a functional opposition attributable to the two extremities of the neurone, based upon its dynamic polarity and upon a physiologic principle which is established by all experi- ments to which the nerve system is submitted, namely, that nerve impuls
. Anatomy, descriptive and applied. Anatomy. THE SPINAL CORD AND BRAIN 811 branches soon after its tlqwrture from the cell; such axoncs ai\- called dendraxones. The axones and their collaterals end in terminal arborizations, tlu' telodendria. The axone is the distriljulive or emissive (cellulifugal) conductor of nerve im|)ulses. There is, therefore, a functional opposition attributable to the two extremities of the neurone, based upon its dynamic polarity and upon a physiologic principle which is established by all experi- ments to which the nerve system is submitted, namely, that nerve impulses pass through the neu- a d rone in a definite direction which is invariable and admitting of anatomic localization. The majority of the peripheral spinal and cerebral axones as well as those constituting the white sub- stance of the brain and cord are invested by a myelin sheath. The Collaterals ().—The collaterals are accessory branchings of the axones which are more numerous in the cyto]5roximal portion and are usually directed at right angles to the parent stem. Some axones possess few or no collaterals, while others possess many. The collaterals, especially those in the gray substance of the central axis, are frequently mye- linic. They unquestionably play an important part in the grouping and chaining of neurones within the system, in yielding up to neighboring neurones a por- tion of the impulse that the cell has received by its dendrites and transmits along its axone to a distance. Varieties of Axones.—Axones are divided into two main groups depending upon the ]3resence or absence of a myelin sheath—(I) myelinic axones and (II) amyelinic axones, or medullated and nomnedul- lated axones. Myelinic axones or medullated axis-cylinder processes are axones enveloped by a relatively thick sheath composed of semifluid phosphorized fat, which gives to the bundles of these structiu'es their opaque, white appearance. The myelin sheath is in tm-n invested by a deli
Size: 923px × 2708px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1913
