A manual of diseases of the nervous system . remities of thesheath is a little clear cementing substance, shownby the fine dotting in the figure. There is onenucleus (n) to each internode, about its middle;hence they are sometimes called internodal the nucleus is a little protoplasm, and itis probable that a very thin layer of protoplasmeverywhere lies between the sheath and the myelin. ,. , .^ Each internode may be conceived as a cell, a fat- inyelm, or white . • , . substance of cell according to Ranvier, consisting of membrane,Schwann; Ac,axis- nucleus, protoplasm, and fatty m
A manual of diseases of the nervous system . remities of thesheath is a little clear cementing substance, shownby the fine dotting in the figure. There is onenucleus (n) to each internode, about its middle;hence they are sometimes called internodal the nucleus is a little protoplasm, and itis probable that a very thin layer of protoplasmeverywhere lies between the sheath and the myelin. ,. , .^ Each internode may be conceived as a cell, a fat- inyelm, or white . • , . substance of cell according to Ranvier, consisting of membrane,Schwann; Ac,axis- nucleus, protoplasm, and fatty matter, the cells b( ingarranged end to end, and the axis-cylinder jiass-ing through them, as a string passes through aseries of tubular beads. The intemodes are shortertowards the termination of a nerve. It is importantnot to confound the nodes with other, imperfectdivisions, sometimes termed the incisions ofSchmidt (IS, Fig. 32,1). These are oblique, incomplete divisionsof the white substance. Many exist in each node. They are believed. Fig. 32.—Diagrumof the structureof nerve-fibres. Iand II, medul-lated, III, non-meduUated fibre ;S, sheath j M, cylinder; n, nu-cltus; N, node;IS, incision ofSt;limidt. (Proma preparation ofthe nerve-fibre ofa f withosmic acid.) PHYSIOLOGY OF NERVES. 47 by some hisfcologists to be of artificial origin, but their uniformcbaracter seems conclusive evidence that they depend on structuralconditions. The myelin, Eanvier suggests, must protect the axis-cylinder, sinceits almost liquid consistence will diffuse pressure on the nerve. Itmay also have an insulating action, which, while not essential forconduction, may render conduction more perfect, and possibly morerapid. The nodal segmentation keeps the almost liquid myelin uni-formly distributed along the fibre, and permits nutrient material toreach the axis-cylinder. The grey fibres, non-me(^ullated fibres, consist of an axis-cylinder, sheath, and nuclei (Fig. 32, III), but contain no
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnervoussystem, bookye
