Vasomotor nerve

“ The quantity of blood in any part of the body at any given time is dependent upon certain relations which exist between the blood-vessels and the nervous system. The walls of the arteries are abundantly supplied with involuntary muscular fibres, which have the power of contraction and relaxation. This power of contraction and relaxation is controlled by certain nerves called vasomotor nerves, because they cause or control motion in the vessels to which they are attached. ”

“ After establishing an artificial circulation of the brain Wiggins found that adding adrenalin to the nutritive fluid reduced the outflow, and it is supposed that adrenalin acts by stimulating the ends of the vasomotor nerves, rather than by stimulating the muscular coats of the arteries. The veins of the pia and dura mater have no middle muscular coat and no valves. The venous blood emerges from the skull in man mainly through the opening of the lateral sinuses into the internal jugular vein ”

“ The blood vessels of certain parts of the body have, in addition to vaso-constrictor nerves, nerves which relax their muscular wall, vaso-dilatator nerves. The latter are never furnished by the sympathetic, they are in the mucous membranes and glands at the oral end of the body furnished by the cranial portion of the autonomic system. In regions at the aboral end of the body they are furnished by the sacral portion of the autonomic system. Elsewhere the vaso-dilatators when present are derived from the nerve-cells of the spinal ganglia (Bayliss) . ”

“ Facility of motor discharge. Great concentration was necessary of course, but not sufficient. Persons in whom the flow of nervous energy tended to drain off over the nerves leading to the glands and the vascular system might betray great tension, not so much by movements as by a flow of perspiration (we have many excellent examples of this given by Manouvrier) [93] or by a violent beating of the heart, blushing and the like,—in short, by secretory and vasomotor effects. ”

“ It is a mistake to try to scramble to one’s feet immediately, because until the vasoconstrictor center recovers its ordinary activity, raising of the head above the level of the rest of the body is bound to result in its failure to receive sufficient blood, and so faintness will come on again. It has long been a practice to dash cold water in the face of a fainting person. The physiological value of this is in the sudden stimulation of the sensory nerves in the face by which is set up a stream of nervous discharges which will play upon the vasomotor center, and arouse it again to activity. ”

“ This necessarily causes a tortuosity of the vessel which can be easily seen in such arteries as the temporals, brachials, radials, and other arteries near the surface of the skin.
The exact mechanism of increase of blood pressure is not satisfactorily explained. The smaller arteries all over the body are supplied with vasoconstrictor and vasodilator nerve fibers from the sympathetic nervous system. Normally when an organ is actively functionating the vessels are widely dilated and the flow of blood is rapid. ”

“ But the mere cessation of vaso-motion will not account for such facts as the rapid and simultaneous development of erysipelatous inflammation, of corneal clouding and ulceration, of iritis and glaucoma, of nutrition-changes in hair and mucous membrane. I must, for the present, be content to believe it probable that there is a special set of efferent fibres in the trigeminus, emanating from the motor-root, whose office it is in some unknown way to preside over the equilibrium of molecular forces in the tissues to which the nerve is distributed ”

“ The heart's action grows feebler, often slower, the pulse weaker; blood-pressure sinks and arterial tension is diminished. Its physiological action is that of a direct stimulant to the heart and the pneumogastric nerve; its toxic action, that of a depressant. Upon the vaso-motor system the action is from the first that of a depressant. Dilatation of capillary vessels and increased afflux of blood manifest themselves in the flushed face, brilliant eyes, and warmth of surface which are familiar phenomena. Frequent repetition tends to permanently impair the activity of the peripheral circulation. ”

“ The vaso-dilator nerves for the limbs issue in the posterior spinal roots (Bayliss) . The posterior roots contain the afferent nerves (touch, pain, &c.) . Excitation of these fibres causes reflexly a rise of blood pressure directly, a vaso-dilatation of the part the nerves supply. Thus it is assured that the irritated or injured part receives immediately a greater supply of blood. The vaso-motor centre exerts a tonic influence over the calibre of the arterial and portal systems.
Much labour has been done. ”

“ The vaso-motor nerves end in a plexus of fibrils among the muscle fibres. Ganglion cells occupy the larger nodes of the nerve plexus. The ends of a torn artery retract, coil up within the external coat and prevent hemorrhage. The arteries contract when mechanically irritated and remain contracted for a long time after excision. They tend to contract when submitted to increased blood pressure. The capillaries cannot contract of themselves, but their lumen can be widened or narrowed by the varying contractility or turgidity of the tissues in which they run. ”

“ Stimulation of the central end of a sensory nerve, e.g., sciatic, brachial plexus, splanchnic, &c., causes a contraction of the renal vessels simultaneous with the rise in the aortic blood-pressure. Stimulation of the central end of the vagus causes a contraction of the kidney (where the vagus of the other side has been cut to eliminate reflex inhibition of the heart) , and the renal vessels contract whether the stimulation of the central end of the vagus cause a rise or a fall of the aortic blood-pressure. ”

“ When the artery is rolled under the finger, then it may seem that there is some thickening in its walls, though it is only heightened blood pressure from emotion that causes the feeling. This high blood pressure may, of course, of itself be an indication of danger whenever there is heart or kidney disease, but it often occurs as a passing event in nervous patients whose vasomotor control is so capricious that arterial tension and blood pressure may change at very short intervals as the result of excitement. ”

“ When there is a sudden rise in the blood-pressure in the arteries, due to vasomotor spasm of the peripheral systemic arterioles, and the heart-walls are strong and well nourished, palpitation is evoked; when the coronary branches are involved in the vasomotor spasm then angina is produced, and the heart-walls, acutely distended with blood, can scarcely contract in the face of the opposition presented to their contraction by the high arterial tension. ”

“ By many writers the vaso-motor nerves seem to be regarded as veritable physiological demons, whose unsleeping vigilance foresees and provides for all local wants; and it is supposed that, while the whole motor force acting on the blood is supplied by the heart's action, these nerves so regulate the caliber of the smaller arteries that they turn on or shut off the blood-current as may seem to be necessary. ”

“ Pressor effects, i.e. those causing increased constriction and rise of arterial pressure, may be produced by stimulating the central end of almost any afferent nerve, and especially that of a cutaneous nerve. Depressor effects are always obtained by stimulating the depressor nerve, and may be obtained by stimulating the afferent nerves under special conditions. That these reflex vaso-motor effects frequently occur is shown by the blush of shame, the blanching of the face by fear, the blanching of the skin by exposure to cold and the flushing which is produced by heat. ”

“ In the absence of plain muscular fibres contraction and dilatation of the capillaries can only be effected by a corresponding contraction and expansion of the nuclei of the endothelial cells. As fibrils derived from non-medullated nerves terminate in small end-butts in connection with the capillary membrane, we may assume that the nuclei of the endothelial cells are under the sway of vaso-motor nerve currents, that weak ones will expand, strong ones contract them. ”

“ Pressure on the nerve arouses its excitability, and compression of the artery shutting off the supply of blood from the disordered and susceptible muscles, tends to increase their irritability. Ligature of an artery supplying healthy muscles causes simple trembling of such organs. From the spasms of cerebral, spinal or meningeal inflammation tetany is distinguished by the absence of fever, and the complete intermissions of the paroxysms. ”

“ In animals, among whom such disorders are rare and whose spinal column is constantly horizontal, there is little or no change in the relative positions of the great organs at any time. In man, who is constantly altering the relationships of these viscera by lying, standing, stooping, the blood supply and venous return are subject to frequent interruptions, and strains are exerted upon the supporting structures of the blood vessels and thus the vasomotor mechanisms are taxed heavily. The head should be permitted to rest as nearly upon a level as the feet, though most people prefer some support. ”

“ There is a reason here, however, which is often left out of sight; not merely is the perpetually varying pressure specially harassing and exhausting to the nerve, but in many of these cases there is general arterial degeneration, and the sensory root of the nerve is exceedingly likely to be very badly nourished. [This result will be more directly brought about when the aneurism happens to press on the ganglion of a posterior root.] ”

“ Increased pulse pressure means increased volume output, but does not always mean increased velocity. The proper distribution of blood to the various organs of the body is regulated by the vasomotor system acting on the small arteries which contain considerable unstriated muscle. In order that there may be enough blood at all times and under varying conditions of rest and function, there must be a proper supply coming through the distributing vessels, the large arteries, those containing much elastic tissue, and only a very small amount of unstriated muscle tissue or none whatever. ”

“ To increase general arterial pressure two methods were used: the spinal cord was stimulated in the cervical region through platinum electrodes, or the left splanchnic nerves were stimulated after the left adrenal gland had been excluded from the circulation. This was done in order to avoid any influence which adrenal secretion might exert. It is assumed in these experiments that vessels supplying active muscles would be actively dilated, as Kaufmann [2] has shown, and would, therefore, in case of a general increase of blood pressure, deliver a larger volume of blood to the area they supply. ”

“ The tone of the vascular system is not disturbed when the great brain and mid brain is destroyed as far as the region of the pons Varolii, but as soon as the spinal bulb is injured or destroyed the arterial pressure falls very greatly, and the animal passes into the condition of surgical shock if kept alive by artificial respiration. Painting the floor of the fourth ventricle with a local anaesthetic, e.g. cocaine, has the same lowering effect on the blood pressure. Division of the cervical spinal cord or of the splanchnic nerves lowers the blood pressure greatly. ”

“ As innervation and circulation go hand in hand or closely follow each other, my own view is that both vaso-motor and molecular changes, temporary in character, probably occur in the central nervous system in grave hysterical cases.
Whatever the temporary conditions are, it is evident, on the one hand, that they are not states of simple anæmia or congestion, and, on the other hand, that they are not inflammations or atrophies. Patients with hysterical manifestations of the gravest kind as a rule are free for a time from their harassing and distressing symptoms. ”

“ The pressure thus exerted on the nerve-cells and fibers will not only prevent their performing their functions properly, but at the same time interfere with their nourishment, and consequently lead to a degeneration of their constituents. The deleterious effects of congestion of the intercranial blood-vessels are rendered apparent to us in yet another way—namely, by the feelings of fullness or tightness of the head experienced by many persons after partaking of alcoholic stimulants. ”

“ Whether from the extension of contiguous inflammation, from external pressure, or from blood tension, the morbid process has much in common; the circulation and nutrition in the vascular walls are interfered with, degenerations set in (softening, fatty, connective tissue) , which predispose to dilatation under the blood pressure. The pouch-like dilatations of the jugular consequent on bleeding, are essentially traumatic. The impaired innervation which lessens the resistance of the vascular walls is not to be forgotten. ”