Motor coordination

“ To accomplish a true reflex movement, a whole mechanism is necessary, set up in the spinal cord or the medulla. To choose voluntarily between several definite courses of action, cerebral centres are necessary, that is, crossways from which paths start, leading to motor mechanisms of diverse form but equal precision. ”

“ To start a mechanism that will produce well-ordered movement, as when I lift this book from the table, impulses or messages, whatever you like to call them, must first be transmitted from the body itself to the brain. Such messages may come to the brain by nerve-fibres from some organ of sense, it may be from the skin, or from the eyes, or from the muscles themselves, but they must be sent to the brain before the brain will send out messages along motor nerves to groups of muscles which are called into action, so as to perform a definite movement. ”

“ The lower motor centers, called also reflex centers, are located in the cord or brain stem, and their nerve cells give rise to the axons that form the motor nerves and connect with the muscles and glands. A muscle is thrown into action by nerve currents from its lower motor center. ”

“ How The Brain Produces Muscular Movements
The motor area is itself aroused to action by nerve currents entering it through axons coming from other parts of the cortex; and it is by way of the motor area that any other part of the cortex produces bodily movement. There are a few exceptions, as, for example, the movements of the eyes are produced generally by the "visual area" acting directly on the lower motor centers for the eye in the brain stem; but, in the main, any motor effect of brain action is exerted through the motor area. ”

“ This psychomotor side of the process, and not the mere muscle activity as such, is indeed the essential factor which should interest us. The results of exercise are a training of the central apparatus of the brain and not of the muscular periphery. The further development of those experiments soon led to complex questions, which referred not only to the mere change in the motor efficiency, but to the learning of particular groups of movements and to the influences on the exactitude and reliability of the movements. ”

“ On the other hand, as a great multitude of motor tracks can open simultaneously in this substance to one and the same excitation from the periphery, this disturbance may subdivide to any extent, and consequently dissipate itself in innumerable motor reactions which are merely nascent. Hence the office of the brain is sometimes to conduct the movement received to a chosen organ of reaction, and sometimes to open to this movement the totality of the motor tracks, so that it may manifest there all the potential reactions with which it is charged, and may divide and so disperse. ”

“ It cannot be used to affect the deep-lying structures, such as the brain, spinal cord, etc. The current-strength is not measured by a milliampere meter. It will produce muscular contraction only through the motor nerve supplying the muscle. ”

“ As Bryan well says, "The efficiency of a machine depends so far as we know upon the maximum force, rate, amplitude, and variety of direction of its movements and upon the exactness with which below these maxima the force, rate, amplitude, and direction of the movements can be controlled." The motor efficiency of a man depends upon his ability in all these respects. Moreover, the education of the small muscles and fine adjustments of larger ones is as near mental training as physical culture can get ”

“ In lifting an object in the hand I can discover no sensation of volitional energy. I perceive in the first place a slight tension about the head, but that this results from a contraction in the head muscles, and not from a feeling of the brain-discharge, is shown by the simple fact that I get the tension on the right side of the head when I move the right arm, whereas the motor discharge takes place in the opposite side of the brain.... ”

“ Closely connected with these facts, perhaps only a somewhat different aspect of them, is the phenomenon of motor mechanization. Any movement repeated tends to become a circular reaction, as it is called; that is, the end of one repetition serves as a cue for the beginning of the next. ”

“ It is the universal motor adapted in the most exquisite manner to every form and state of the lungs, which communicate their general motion to every part of the body, and set every wheel in its infinitely complex organism revolving upon its axis, and give to every muscle and nerve the power to expand and contract and vibrate in the performance of its use, and in this way to fill every organ in the whole universe of the body with the power of sensation. ”

“ The circuit which connects any one single perception with action, through sensory nerve, sensory centre, motor centre, motor nerve and muscle, is as purely mechanical as that of an electric circuit. Reflex motions such as breathing, and even more complex motions which by repetition have become reflex or instinctive, are also mechanical and involve no exercise of will. ”

“ A movement of attack has succeeded the simple movement of defence, and indicates a complete change in the nature of the motor reaction. In the first case the limb is withdrawn briskly from the painful stimulus; in the second the animal performs a series of co-ordinated purposive movements. The first reflex is automatic, and so no doubt is the second, since the frog is decerebrate. But a co-ordinated movement is not of necessity automatic from the outset; its automatism may be the sequel to voluntary education. Co-ordination is often a manifestation of cortical activity. ”

“ To learn swimming or skating by simple cogitation or mere visual observation is of course impossible. The new ideas requisite cannot be constructed without motor experience, and the training must include that motor experience. Hence the training for a new skilled motor manœuvre must be simply ad hoc, and is of itself no training for another motor co-ordination. ”

“ From the motor nerve-cells an impulse or command travels by motor nerve-fibres, one from each cell, to the muscles, which contract. If this took as long to happen as it takes to describe, even in outline, it would not be of much use to the earthworm. But the motor answer follows the sensory stimulus almost instantaneously. The great advantage of establishing or enregistering these reflex chains is that the answers are practically ready-made or inborn, not requiring to be learned. It is not necessary that the brain should be stimulated if there is a brain ”

“ We must remember that there exist at the base of the brain motor centres which serve to intermediate between the will and external acts. The will calls into action such or such centres, and these immediately determine the action of certain muscular groups. We know besides, that, according to the habits and education of the muscles, particular muscles can enter only with great difficulty upon isolated movements, and that the contraction of one muscle sometimes forces the contraction of others, even against the will. ”

“ For example, it is difficult to come to an understanding respecting the motor and sensory nerves, so long as we continue to talk as if we believed that "motility" resides in the spinal chord, and that the posterior roots are "sensitive." Motor force no more resides in the spinal chord, than explosive force resides in the lighted match; the motor-force is in the muscles, the explosive force is in the gunpowder ”

“ This, however, is not the case, but the strength of the motor sensation is purely proportional to the strength of the impulse to movement, which starts from the central organ innervating the motor nerves. This may be proved by observations made by physicians in cases of morbid alteration in the muscular effect. A patient whose arm or leg is half paralyzed, so that he can only move the limb with great effort, has a distinct feeling of this effort: the limb seems to him heavier than before, appearing as if weighted with lead ”

“ But while each motor center is thus connected by motor or efferent fibers with the muscles, recent work by Sherrington and Mott and by other observers has shown that it is also connected by sensory or afferent fibers with the muscles, the skin overlying them, the joints in their neighborhood, and the bones which they move. The 'motor area,' in fact, is not purely motor, but has sensory functions as well. ”

“ We conclude, accordingly, that perception of an object is not absolutely the same thing as motor response to the object, nor even as motor readiness to respond, although the transition from perception to motor readiness may be so quick that the whole reaction seems a unit. In reality, perception of the object precedes the motor adjustment, and is one factor in determining that adjustment. ”

“ This last tract is the main medium by which impulses initiated by electrical stimulation of the motor cortex reach the moto-neurones of the cord and through them influence the activity of the skeletal muscles. Of the function of the other tracts descending from the brain into the cord little is known except that mediately or immediately they excite or inhibit the spinal moto-neurones by various levels. How they harmonize one with another in their action or what their purpose in normal life may be is at present little more than conjecture. ”

“ Many physiologists claim that these cells are only excitable by the will. For the theory of motor centers they substitute that of psycho-motors. Reserving this discussion for another time and place, we may say that, whether we excite the cells or the fibers that arise from them, the result is the same.
All stimulation, whatever its nature or origin, acts upon a nerve according to its functions. Excite a motor nerve at any point of its course, and you produce movement; excite a sensory nerve, and the subject will feel a sensation which will vary with the nature of the nerve. ”

“ To say that motor-habits, with which when they are established consciousness may have little to do, can be registered in a flexible motor instrument and acted over and over again, is reasonable enough ”

“ It is, in the cases noted, at once sensory and motor, or at any rate involves motor elements. And the effect of the activity of such motor elements is both to increase the distinctness of the image and to prolong the duration of the process by which it is apprehended. The sensory process thus stands in intimate dependence on the motor. Nor would failure to move the eyes or any other organ with the movement of attention, if established, be conclusive as against the presence of motor elements. A motor impulse or idea does not always result in apparent peripheral movement. ”

“ Thus not only the motor, but the sensor nervous system also, and the mental functions, are capable of being exercised and need it; and the muscles again appear to acquire a deeper importance in gymnastics. ”

“ The nerves of the senses are not polar, do not therefore excite the brain, nor does this again affect the motor system. The muscle therefore arrives at a state of non-tension; it becomes relaxed, and along with it necessarily the organs of sense, which are thrown into activity by muscular motion. The arms and fingers, whose business is to touch, sink down; the feet which move, and thereby warm and animate the body, are slackened and bent together; the body is in the recumbent posture ”

“ The truth is that the muscles have nothing to do with the passage of the mental currents or waves from the Transmitter to the Receiver any more than they have to do with the transmission of nervous sensations from body to brain, or the motor impulses from brain to body. When you wish to close your hand you send a nervous current from your brain to the muscles controlling your hand. The current travels along the nervous system, and is by it distributed over the muscles causing them to contract. A current from a galvanic battery will cause the muscles to act in the same way. ”

“ It is rarely only one muscle that is thus excited to activity, there are usually several, and here we have the transition to instinctive action, which consists in a longer or shorter series of actions, that is, of motor combinations. These, too, are originally, at least, set a-going by a sense impression, an external stimulus which affects a sensory nerve exactly in the same way as in the reflex mechanism, and this stimulus is carried to a particular group of sensory nerve-cells in the central nervous organ, and from these transmitted by very fine inter-connexions to motor centres. ”

“ When the excitant is moved about over the different convolutions, the existence of the motor zone is made manifest by the successive movements of the animal; the sensitive zone is known by signs of sensation, while the indications of an intellectual zone are not thus positive. Observe what passes when we irritate the so-called motor region. We excite a certain point of the convolutions, and a movement is produced. Groping about with our electrodes, we find the effect limited to a small tract where at all the points the same movement is provoked, and that alone. ”

“ Thus, a sensation is propagated along the sensory nerve to the sensory nerve-centre, whence it is transmitted to the motor-centre, which acts as an accumulator of stored-up energy, a large flow of which is sent through the large conductor of the motor-nerve to the muscle, which it causes to contract and thus produces motion. It is thus that the simpler involuntary actions are produced by a process which is purely mechanical. In the more complex cases, in which consciousness and will are involved, the process is essentially the same, though more complicated. ”