On Motor and Sensory Nerve Systems in in Lumber Cord in Man

Abstract

Motor cells exist in the lumbar cord not only in cornu ventrale, but also in pars intermedia and cornu dorsale, and they are clearly distinguishable from the vegetative and sensory cells, through that they are very large in size, show a concave contour and are provided with many stout processes, giving them an appearance of rugged virility. Motor cells incornu ventrale are especially typical in their form. They have usually one long process each, which is thick and strongly stainable, but seeing that the total number of long processes is. larger than that of motor cells on the same cross section, it may be surmised that some cells send out two long processes each, or some of the processes branch out in 2 rami. The short processes number 5 to 7 per cell, are stout but somewhat weakly staining, and after a rather long course, mostly branch out in numerous rami and apparently end freely. Frequently, true anastomosis of short processes is observed between both motor cells. Motor cells in cornu ventrale may be divided into the medial and lateral groups. The cells in the former group are smaller both in number and size than the cells in the latter group. The former can be divided again into the ventral and dorsal subgroups. The dorsal subgroup is especially poor in development. The lateral group, on the other hand, is very well developed, and can be divided into the ventral, middle and dorsal subgroups, and especially in the lumbar swelling the number of motor cells increases, so that they may be justly subdivided further. Motor cells in pars intermedia are arranged sporadically, with prevalence in its medial parts, where 3 cells are usually seen on one cross section. In shape, they resemble the small motor cells in the medial group in cornu ventrale. Motor cells in cornu dorsale are seen in its lateral, medial and basal parts, where 1 or 2 each are found in the respective areas. They are also small in size. Motor cells in cornu ventrale, together with their long and. short processes, are found buried in a plexus of incoming nerve fibres. Of the plexus fibres, the motor fibres penetrate into the motor cell group chiefly through the tractus corticospinalis lateralis, the reflex sensory fibres through the entrance zone of dorsal root fibres, and the minute vegetative fibres from the circumference of the cell group. These fibres are all thinner than the short processes of motor cells. The incoming motor and sensory fibres are both better stainable and stouter than the vegetative fibres, so that the distinction between them is readily made. The end formation of these incoming fibres toward the motor cells is neither represented by pericellular reticular formation nor by annular or pin-head shaped corpuscles, as has been held hitherto, but by an intricate criss-cross run in every direction of the incoming fibres. They seem to end in simple branched endings around the short processes, rather than around the cell bodies. The transmission of stimuli seems to be accomplished by the following process. First, the stimuli carried by the incoming fibres excite the glial cells apparently of endocrinous nature, whose secretion secondarily excites the motor cells, in particular their short processes. The excitement ofthe motor cells is then transmitted by the way of the long processes to the periphery. Sensory cells in the lumbar cord stand midway between the motor and vegetative cells in size, and are morphologically readily distinguishablee from the latter two. Only few of them are rounded and feminine in appearance as those in the sensory nuclei in the brain stem, the majority being either spindleshaped or triangular in form. Their short processess are strongly stainable and stout, but stand behind those of motor cells both in number and length. They apparently end without branching or in a few branches, always sharply. These sensory cells are different in size and shape according to their localisation.