12 See Fürstner, Arch. für Psych., xiv. 422.
Vaso-motor Tracts.—These reflex centres are connected with the medulla by tracts which lie in the lateral columns of the spinal cord,13 although it is not determined in which part of these columns. It is not possible as yet to separate the constrictors from the dilators in this tract, nor to determine whether it transmits impulses in both directions or only from above downward. Nor is the course of associating fibres between reflex centres at different levels known. In cases of transverse myelitis the control of the medulla is removed from the vascular centres below the lesion, and the lack of vascular tone seen in the paralyzed limbs, together with the susceptibility to local irritation, is the result of this division of the vaso-motor tracts.
13 “Owsjanikow and Tschirijew,” Bull. de l'Acad. de St. Petersbourg, xviii. 18.
Medullary Centres.—It has been stated already that a general vaso-motor centre with both constrictor and dilator powers is situated in the medulla. This lies in two divisions on each side of the middle line, in or just beneath the floor of the fourth ventricle, from the calamus scriptorius up to the level of the sixth nerve-nucleus. Each division governs the vascular tone of its own side of the body,14 and lesions in its region in man produce unilateral vaso-motor symptoms.15 This centre can be excited to reflex action by strong irritation locally or through the blood, in which case a general constriction or dilatation of the vessels of the entire body will ensue. It seems probable, however, that the general centre in the medulla is made up of a number of special centres, each of which governs a definite set of organs. The vascular tone of the thoracic and abdominal viscera is certainly regulated by a series of such centres. Brown-Séquard and Schiff have produced hemorrhages in the lungs, pleura, stomach, intestines, and kidneys at different times by destructive lesions of the medulla, and the well-known experiments of Bernard, in which by puncture of the medulla local hyperæmia of the liver or kidneys was caused, producing glycosuria or polyuria, confirm this view. Lesions of these parts in man produce similar effects. Charcot has shown that in cerebral hemorrhage ecchymoses may be found in the stomach, pleura, and endocardium, and that pneumonia is especially frequent upon the paralyzed side. De Jonge16 has been able to collect thirteen cases of diabetes mellitus in which a lesion of the medulla (hemorrhage or tumor) was found after death; and Flatten17 has proven the existence of similar lesions in diabetes insipidus. The connection of these centres with the liver and kidneys has been traced elsewhere.18 The medulla contains a special centre for the vaso-motor nerves of the abdomen, which are in the domain of the splanchnic nerves. This centre is excited reflexly by impulses reaching it through the depressor nerve of Cyon from the heart; so that when that organ is overburdened it may be relieved by a fall of arterial pressure produced by dilatation of the abdominal vessels. Whether the connection of the medulla with the centres in the semilunar ganglion which preside directly over these vessels is made by way of the spinal cord or by way of the pneumogastric nerve is still undetermined, though the researches of Gaskell favor the former view. Gastric and intestinal disturbances are certainly produced by nervous lesions in the medulla, but whether they are due to vascular changes is uncertain. The vomiting of mucus and blood, and the large watery evacuations which accompany mental shock or anxiety, as well as the polyuria associated with mental effort, have been ascribed to irritation of local centres in the medulla governing the gastro-intestinal and urinary organs by impulses received from the cortex above. The spleen is under the control of vaso-motor centres, since section of the splenic branches of the semilunar ganglia will produce a great enlargement of the organ, and irritation of the cut end of these branches will produce contraction.19 The medulla also contains a vaso-dilator centre for the erectile tissues of the genital organs, irritation of which by mental action or local disease causes impulses to pass to the nervi erigentes by way of the spinal cord, resulting in a flow of blood to the parts. Although a centre has been thought to exist controlling the circulation in the lungs, whose paralysis has been supposed to explain the occurrence of sudden pulmonary œdema without other known cause, no definite facts regarding it are known. That the action of the heart is under the control of the medulla is a fact too well known to require more than a mention. The physiology of the nervous control of the heart cannot be discussed here.
14 Owsjanikow, Arbeiten aus d. Physiol. Instit. zu Leipzig, 1871.
15 M. A. Starr, “Sensory Tract in Central Nervous System,” Journ. Nerv. and Ment. Dis., July, 1884, pp. 396-398.
16 Arch. f. Psych., xiii.
17 Ibid.
18 See Tyson, “Diabetes Mellitus,” Pepper's System of Medicine, Vol. I. p. 195; Edes, “Diabetes Insipidus,” ibid., Vol. IV. p. 30.