Magnus-Kleijn Reflexes

Magnus-Kleijn reflexes (Magnus, de Kleijn) are tonic reflexes that coordinate the position of the trunk and limbs with the position of the head. The work of Magnus and his colleagues, mainly de Kleijn, showed that in the brainstem there is a complex system of reflex centers that ensure the maintenance of body positions and its return to the original position. These reflexes are divided into two large groups depending on whether they concern the maintenance of equilibrium of the body and its parts or the reaction to movements. Those reflexes that maintain the equilibrium of the body during standing, sitting, and lying are called static reflexes; those reflexes by which the organism reacts to active and passive movements and which partly compensate for the displacements occurring during them are called statokinetic reflexes. Static reflexes in turn can be divided into two large groups. At rest, the body assumes a certain posture determined by the regular distribution of tension throughout all muscles and a certain tonic fixation of individual parts of the limbs and trunk in various joints. Static reflexes that determine the posture of the body at rest are called position reflexes. The second group includes those static reflexes by which the body is able to return from various positions to the normal position. These reflexes are called setting reflexes. Position reflexes are studied on decerebrated animals, because decerebration (see.) eliminates setting reflexes, the center of which is located higher (midbrain, red nuclei), and thus allows the study of position reflexes in isolation. Here, first of all, the influence exerted on the general position of the body by the position of the head should be noted. In this case, it is necessary to distinguish between two kinds of influences. By changing the position of the head, one first changes its relation to the trunk, and secondly, produces a change in its position in space and thereby stimulates the vestibular apparatus. In the first case, it is a matter of the action of reflexogenic impulses created by irritation of the neck muscles - tonic neck reflexes, studied after preliminary destruction of both labyrinths. In the second case, labyrinthine reflexes are spoken of. For their study, fixation of the neck (bandage) is necessary, which eliminates the action of neck reflexes - Neck reflexes: turning the head strengthens the extensor tone in the limbs toward which the chin is turned and the flexor tone in the opposite limbs; bending the head leads to an increase in flexor tone, extension of the head - to an increase in extensor tone. In contrast to neck reflexes, labyrinthine reflexes always change the tone of all four limbs in the same direction. In addition to the tone of the limbs, labyrinthine reflexes also change the tone of the neck and trunk muscles and are particularly important for maintaining equilibrium. By acting on the neck muscles, labyrinthine reflexes cause their tension and thus secondarily cause the occurrence of neck reflexes. Therefore, one should speak of direct and indirect (through neck reflexes) influences of the labyrinth on the tone of the limbs. Labyrinthine and neck irritations also lead to changes in the position of the eyeballs, affecting the distribution of tension in the eye muscles. The tonic labyrinthine reflexes of this group cause, when the position of the head in space changes, such a movement of the eyeballs that they seem to strive to maintain their initial position. Quantitative measurements show that labyrinthine impulses are not sufficient to fully achieve this goal, and neck impulses must also be added. Just as in relation to the muscles of the trunk and limbs, and in relation to the eyeballs, labyrinthine and neck reflexes show algebraic summation. Setting reflexes. Animals in which the midbrain is preserved, in addition to those described, also exhibit setting reflexes. In other words, animals that have preserved the area of the red nuclei can not only maintain their posture due to the reflexes described, but can also return to the normal position if it is disturbed. A decerebrated animal stands if placed, falls if pushed, and cannot rise to its feet by itself; an animal with an intact midbrain, on the contrary, can return from any position to the normal position. In this setting function, many reflexes, the starting point of which are various receptor organs, also participate. First of all, labyrinthine setting reflexes are included here. For their study, the animal is subjected to preliminary transection of the brainstem above the level of the red nuclei. If such an operated rabbit is grasped in the pelvic region and held freely in the normal position in the air, then the front part of its body and head are in a completely correct posture, so that the back of the head is directed somewhat upward and the oral opening is somewhat below the horizontal. If, from this position, the pelvis is rotated around the frontal axis so that the sacrum assumes a vertical position and the oral end is directed upward or downward (a difference of 180°!), then in these positions the head of the animal does not change or hardly changes its position in space. Quite the same when rotating the pelvis around the vertical axis to the sides up to 180°, the position of the head in space does not change, because it performs compensatory rotation in the opposite direction. After extirpation of both labyrinths, all these reflexes disappear: the position of the animal can change in any direction, the head does not return to its original state. But if such a labyrinth-less animal is brought into contact with a table, then new reflexes leading to the same effect as labyrinthine ones are found in it. These so-called body reflexes are explained by the asymmetric irritation of the sensory nerves of the trunk and limbs - it is sufficient to make such irritation symmetrical by pressing a board on the free surface of the lying animal for them to disappear. After the head, the body must assume the normal position. This is achieved by neck setting reflexes, thanks to which first the front and then the back part of the body follow the changes in the position of the head. In essence, a whole chain of reflexes successively conditioning each other arises. But the body in its return to the normal position depends not only on these reflexes. If a rabbit is placed on its side on a table and its head is held in this position by force, then even under these conditions the body often assumes the normal position. Thus, here it returns to the normal position despite the neck setting reflex, which strives to keep it in the lateral position. Here too, reflexogenic impulses originate from the asymmetric irritation of the body surface. In general, thus, both the head and the body can be brought into the normal position by means of a double reflex mechanism: the head - by means of labyrinthine reflexes and those reflexes that are excited by asymmetric irritation of the body; the body - by means of neck setting reflexes, as well as those reflexes that are excited by asymmetric irritation of the body. The centers for the 4 setting reflexes mentioned are located in the midbrain and partly in the area of the pons Varolii. The second large group of reflexes described by Magnus consists of statokinetic reflexes, i.e., reflexes caused by active or passive movements. First of all, labyrinthine reflexes caused by rotation of the body are included here. Their study in humans has acquired great practical importance (diagnosis) through the work of Barany (Barany). If an animal is placed on a rotating disk so that its spine is directed along the radius and the head is turned toward the periphery of the circle, then rotation of the disk to the right causes the head to turn REFLEXES

520 to the left: rotational reaction of the head. Upon cessation of rotation, the head turns to the right: sequential rotational reaction of the head. With the same experimental setup, changes in eye position are also observed. During rotation to the right, the eyes deviate to the left, and upon cessation of rotation, to the right: the ocular rotational reaction and sequential reaction. By changing the animal's position and the direction of rotation, vertical and rotatory deviations can also be obtained. Finally, similar rotational reactions are observed from the trunk and limbs, especially in monkeys, in which their labyrinthine origin can be easily demonstrated.-In addition to rotational reactions, labyrinthine reactions to simple (non-circular) translational movement are also distinguished. If an animal is placed on a board and this board is moved vertically upward, at the beginning of the movement the limbs, especially the forelimbs, flex, and upon cessation of movement, on the contrary, extend: the lifting reaction. If a guinea pig with its head downward is supported in the air and slightly displaced downward, its forelimbs move in an oral direction and assume a position that can support the body weight upon contact with the ground: the jumping reaction. All the described reactions disappear after removal of the labyrinth.-In addition to labyrinthine reactions, the group of statokinetic reflexes also includes reactions to movements of individual parts of the body. Their number is large; the reflexogenic impulse causing them is irritation of the deep nerves of the trunk and limbs. In recent years, great attention has been paid to the study of Magnus-Kleijn reflexes and similar ones in humans, and they are beginning to acquire increasing importance in the clinic of diseases of the central nervous system. They appear with great clarity in embryos (Minkowski) and in the early period of extrauterine life (Schaltenbrand). This includes, for example, the Landau reflex: the child is held in the air by the researcher's hand with the back upward (the chest rests on the researcher's hand); the head extends at the same time, the spine also extends, and the lower extremities, so that the entire body takes the form of an arc open upward (6-8 months after birth). This also includes the Moro reflex: to shaking of the bed, to tapping on the abdomen, etc., the child responds with extension and abduction of the limbs and then, in the second phase of the reflex, their adduction and flexion.-The reflexes of the Magnus type are much weaker in the adult with an intact nervous system. But they can reappear with great clarity under certain pathological conditions, thereby acquiring significant diagnostic value. In the normal adult, the main reactions of the Magnus type are as follows: 1) the basic experiment of Shilder: rotation of the head to one side with arms extended and eyes closed (eyes remain closed in all subsequent experiments) leads to rotation of the trunk and deviation of the arms in the same direction and lifting of the corresponding upper extremity upward; 2) spontaneous lifting reaction - extended forward arms are spontaneously lifted upward, the right often higher than the left; 3) spontaneous divergence - under the same conditions, the arms diverge to the sides; 4) pronation phenomenon - arms are extended with palms upward, spontaneous pronation; 5) position retention - arms are extended forward, with one held horizontally, the other arm at 60° above or below; after 30 seconds, the subject should bring the second arm to the level of the first (horizontal); the task cannot be accomplished; in the first case, the arm ends up several centimeters above, in the second case below the horizontal, although the subject feels that he has brought the arms to exactly the same level. Under pathological conditions, the above phenomena may weaken, strengthen, or become perverted. Simons, one of the first to draw attention to the presence of Magnus-Kleijn reflexes in humans, showed that in hemiplegias, turning the head to one side leads to a change in the form of global synkineses, strengthening, depending on the experimental conditions, either the flexor or extensor tone. Furthermore, the research of a number of authors showed that reflexes of the Magnus-Kleijn type are strengthened in cerebellar lesions, and specifically, on the side of the lesion, the basic experiment, spontaneous lifting reactions, divergence, and pronation are strengthened. As special symptoms of the same group, the hyperflexion phenomenon and the imitation phenomenon appear in this context. Hyperflexion phenomenon: the heel of one foot should touch the knee of the other foot, which before the experiment is in a position of extreme flexion - the experiment fails, the heel touches a point above the knee. Imitation phenomenon: one leg is flexed at the knee and rests its heel on the bed, the other leg should be brought into a similar position from a position of extreme flexion or extension - the experiment fails, the imitating leg is always more flexed than the imitated one. Sometimes in cerebellar lesions, the matter may also go to the perversion of normal reactions. Thus, the basic experiment can be perverted in the sense that head rotation leads to deviation of the upper extremities in the opposite direction.-Weakening of reflexes of the Magnus-Kleijn type, as well as their complete disappearance, are observed in striopallidal syndromes (parkinsonism).

Lagereaktionen bei Kindern, Deutsche Zeitschr. f. Nervenheilkunde, B. LXXXVII, 1925; Simons A., Kopfhaltung und Muskeltonus, Zeitschr. f. d. ges. Neurol., B. LXXX, 1922.