. Cunningham's Text-book of anatomy. Anatomy. Nerve - fibres. â- Nerve - fibres, ar- ranged in bundles of greater or less bulk, form the nerves which pervade every part of the body. They also constitute the greater part of the brain and spinal medulla. Nerve-fibres are the conduct- ing elements of the nervous system ;â they serve to bring the nerve-cells into relation both with each other and with the various tissues of the body. There are different varieties of nerve- fibres, but in all the leading and essential constituent is a delicate thread-like axon. The most obvious difference between i
. Cunningham's Text-book of anatomy. Anatomy. Nerve - fibres. â- Nerve - fibres, ar- ranged in bundles of greater or less bulk, form the nerves which pervade every part of the body. They also constitute the greater part of the brain and spinal medulla. Nerve-fibres are the conduct- ing elements of the nervous system ;â they serve to bring the nerve-cells into relation both with each other and with the various tissues of the body. There are different varieties of nerve- fibres, but in all the leading and essential constituent is a delicate thread-like axon. The most obvious difference between individual fibres depends upon the nature of the covering of the axon. When it is coated on the outside by a more or less thick sheath of a fatty substance, termed myelin, it is said to be a myelinated or medullated fibre. When the coating of myelin is absent, the fibre is termed a non-myelinated or a non-medullated fibre. A second sheathâthin, delicate, and membranous, and placed externally âmay also be present in both cases. It is termed the primitive sheath or the neurolemma. From a structural point of Fig. 448.âTwo Multipolar Nerve- cells (from a specimen prepared by the Golgi method). view, therefore, four different forms of nerve-fibre may be recognised:â Non-med ullatedâ 1. Naked axis-cylinders. 2. Axis-cylinders with primi- tive sheaths. Medullatedâ 3. Primitive sheath absent. 4. Primitive sheath present. Every nerve-fibre near its origin and as it approaches its termination is unprovided with sheaths of any kind, and is simply represented by a non- medullated naked axis- cylinder. The fibres of the olfactory nerves afford us an example of non - medullated fibres furnished with a primi- tive sheath. Medullated fibres are present in greater quantity in the cerebro-spinal system than non-medullated fibres. Thus, FlG all the nerves attached to the. 449. â Nerve-cell from Cerebellum (Cell of Pctrkinje) SHOWING THE BRANCHING OF THE DENDRITIC PROCESSES (from a photogr
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
