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OBSEBVATIONS on SBNSOEY NERVE-ENDINGS in VOLUNTARY MUSCLES. THEEB Are at Least Three Kinds of Sensory End Organs in Voluntary Mu

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OBSEBVATIONS on SBNSOEY NERVE-ENDINGS in VOLUNTARY MUSCLES. THEEB Are at Least Three Kinds of Sensory End Organs in Voluntary Mu OBSEBVATIONS ON SBNSOEY NERVE-ENDINGS IN VOLUNTARY MUSCLES. Downloaded from BY ANGELO BUFFINI. Lecturer on Microscopical Anatomy, Royal University of Bologna. THEEB are at least three kinds of sensory end organs in voluntary muscles. Of these the most important is the http://brain.oxfordjournals.org/ muscle-spindle, and next to it comes the tendon organ; besides these the muscles possess a certain number of Pacinian corpuscles. I.—MUSCLE-SPINDLES. From the bistological and physiological facts which we now possess regarding muscle-spindles, there can, I think, by guest on June 8, 2016 no longer be a question as to their nature being sensorial. It was already, in 1888, conjectured by Kerschner, but Kolliker in the following year rejected his arguments. In 1892 I myself was able to strengthen the view by con- tributing for the first time an accurate histological descrip- tion of the nerve-ending; and in 1893 Sherrington actually demonstrated the existence of sensory nerves in muscle, and in the following year, by indisputable data obtained by experiment and microscopy, finally furnished conclusive proof that the spindle is an organ of sense In the past two years I have had the opportunity of preparing a large series of specimens of muscle-spindles from the cat. These have yielded me interesting results, which I will here summarise. In the muscle-spindles of the cat there exist three distinct types of nerve-endings, which I will call respectively the primary, secondary, and plate endings. SENSORY NEBVE-ENDINGS IN VOLUNTARY MUSCLES. 369 The Primary Form of Ending.—This is the nerve- ending which I described minutely and figured in 1892, and Sherrington has confirmed my description of it. The large nerve-fibre which goes to form thia ending just before it joins the spindle, almost always divides into two or more secondary branches ; these branches, after having passed through the capsule of the spindle, divide into tertiary branches, each of which approaches a muscle-fibre in the intrafusal muscle-bundle, and terminates on it. The myelin Downloaded from sheath is lost on the tertiary branches, and each then becomes broad and flat and riband-like, and then either winds spirally round the muscle fibre or runs along one side of it as a longitudinal band from which, from point to point and at varying intervals, troop-like terminal ex- http://brain.oxfordjournals.org/ pansions clasp the entire circumference of the fibre. Both these two modifications may co-exist and even lie juxta- posed in one and the same fibre. That is why it seemed, and still seems, to be well to give that ending the name of annulo-spiral ribbon ending. At the two extremities of this annulo-spiral ribbon ending the nerve terminates in diverse swollen knobs. The Secondary Form of Ending.—Besides the primary by guest on June 8, 2016 there is found another form of ending distinct from it in morphological character and in the individuality of the nerve- fibre whence it springs. It has not yet been described in any paper, but I have known of it for some years. The parent nerve-fibre here also divides into secondary branches, but usually only after having penetrated the spindle. The secondary branches soon break up into a number of varicose axis-cylinders, united by very delicate and short filaments. The varicosity of the nerve-fibrils is of various kind, rounded, bifid, triangular, leaflet-like, &c.; the varicosities seem always disposed in such a way as to recall the arrangement of a festoon-wreath of flowers. Hence I call this form of ter- mination the flower-wreath ending. The terminal expan- sions of the axis-cylinders of these nerve-fibres lie on the intrafusal muscle-fibres, but are hardly ever possessed of such long stalks as those of the primary ending. The Plate Ending.—The size of these endings is extra- 370 OBIGTNAL ABTICLES AND CLINICAL CASES. ordinarily variable. One finds some instances smaller than motor end-plates, some equal in size and some much larger; the last-named are the most usual. There is a difference between these and the ordinary motor end-plates; the terminal expansions of these plate-endings are attached to short and extremely delicate filaments, so that they form, as it were, chaplets, in which rounded axis-cylinders and cross-pieces of the finest delicacy succeed each other in turn. The chaplets which compose a plate-ending anas- Downloaded from tomose one with another by minute filaments, and at the extreme margin of the plate terminate with obvious enlarge- ments that are rounded off, on this side turned away from the plate. It is usual for a single individual fibre to pass to each plate-ending. http://brain.oxfordjournals.org/ I have not met with each of the above-described endings in every spindle; it is for that reason that it seems to me important to distinguish three forms1 of "spindles": (1) The spindle with complex nerve-ending; (2) the spindle with simpler nerve-ending; and (3) the spindle with simplest nerve- ending. In spindles of the first class there co-exist a primary form of ending, two secondary forms, and as many as twenty or more of the plate-endings. The primary end- by guest on June 8, 2016 ing and the two secondary are almost always found very near together; the plate-endings are set at various dis- tances, some in the proximal and some in the distal parts of the spindle. In spindles of the second class there occur a single primary form of ending, a single secondary form of ending, and a number of plate-endings, set as in the spindles of the first class. In spindles of the third class there exist a single primary form of ending and a few plate endings, always arranged as in the spindles of the two other classes. From this it is clear that, firstly, the primary form of ending, the annulo-spiral ribbon, is met with constantly in all spindles of the cat; secondly, that the secondary form of ending is that which can vary and even be wanting alto- 1 Aooad. Medico-fisioa di Firenze, February, 1896. SENSOBY NEBVE-ENDINGS IN VOLUNTABY MUSCLES. 371 gether. Hence the nomenclature I have ventured to propose and adopt. Of the three classes of spindles examples are not met with equal frequency. In the cat, examples of class 1 are the most numerous; examples of class 2 the least numerous. To the two older views which considered, on the one hand, that the muscle-spindle was an embryonic centre for the development of new muscle-fibres, or, on the other, a pathological product, we cannot, and ought not, to-day to Downloaded from allow anything more than a historical value. They are opinions which we have had, of necessity, to discard as our knowledge of these special nervous organs has progressed. Sherrington, besides having furnished some valuable addi- tions to our knowledge of the structure of these organs, has http://brain.oxfordjournals.org/ succeeded in demonstrating, by means of his experiments, that the myelinate nerve-fibres ending in them suffer no damage after the complete destruction of the anterior (motor) spinal nerve-root, and has proved that the nerve- fibres in question take their origin in the cells of the spinal ganglia. If to this experimental result be added now the new data afforded by my anatomical observations, it will be clearly evident that there is an indisputable basis of truth by guest on June 8, 2016 for the new view that the muscle-spindle is of sensorial nature. II.—TENDON OBGANS (GOLGI OBGANS). In 1892 I called the attention of histologists to two forms of nerve-ending that can be found in the tendon organs. The few observations which I then published I have since largely added to, and have further extended my enquiry to the structure of the tendon of the musculo-tendon organ, with the view of throwing light on certain facts which were laid stress upon by A. Cattaneo and Ciaccio. Together with the nerve-fibre proper to the Golgi tendon organ I find in the cat another much thinner myelinite nerve-fibre accom- panying the proper fibre. I call this the concomitant fibre. This fibre, arrived in contact with the mosculo-tendinous 372 OBIGINAL ABTICLE8 AND CLINICAL CASES. organ, loses the myelin sheath, and begins to undergo sub- division into a number of secondary fibres, and these latter are so tenous that only a very perfect reduction can reveal them in the preparation. These excessively minute fibres do not anastomose one with another, but they do form a plexiform network, more or less extensive, though never very extensive, because the number of their subdivisions is never very great. Generally they follow a direction from the tendinous end toward the muscular end of the Golgi Downloaded from organ, and terminate close to where the tendon passes into muscle-fibre, or in the muscle-fibre, even at some distance from the tendon of the organ. Their mode of ending con- sists in the formation of an apical beaded chaplet, the end bead being much larger than the more proximal. This http://brain.oxfordjournals.org/ ending sometimes can be seen to be not on the muscle-fibre proper, but on the membrane which Sherrington names the axial sheath, because it lies within his periaxial space. It seems, in fact, to me that these concomitant fibres, with their twisting course outside the Golgi tendon organ, adhere to it rather than strictly speaking penetrate it or belong to it. The existence of the above-described plexiform nerve- ending may be really rare, or its rarity may be only a seem- by guest on June 8, 2016 ing one, on account of the difficulty of regularly obtaining the exquisite and indispensable delicacy of reduction re- quired to make it visible to the eye of the observer.
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