Motor function

“ The particular function of the elements which are substituted for geometrical symmetry has been made clear; their presence lends variety and richness to the balance of motor impulses. But the natural motor response to stimulation has another characteristic which belongs to us as individuals. The motor response must be balanced, but also unified. In a picture, therefore, there must be a large outline in which all the elements are held together, corresponding to this requirement of unity. ”

“ Admitting the need of meeting these requirements; admitting again that we have little evidence that animals are dextral in their functions; admitting also the known results as to the control of the two halves of the muscular system by the opposite brain hemispheres respectively; admitting further that the motor speech function is performed by the hemisphere which controls the stronger side of the body, and is adjacent to the motor arm center in that hemisphere ”

“ The motor attitude of the animal towards the excitations of the external environment constitutes the predominant part of its objective world. The reactions with their sensori-motor effects are part and parcel of the total percept. Sensori-motor life gives reality to the world of objects. The spatial, the resistant, the material character of objects depends on our motor reactions which give content and reality to the world of things. ”

“ So apparently insignificant is the sensory side and so predominant is the motor side with its almost mechanically fatal reactions, that some physiologists put the whole mechanism of excitation and reaction in the lower animals under the category of tropisms, which may be positive or negative, according as the animal goes to or from the particular stimulus. ”

“ The lower we descend in the scale of animal life, the more prominent do the motor reactions become. Where life is predominantly of the instinctive type, the motor side of consciousness is more apparent. ”

“ 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. ”

“ 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. ”

“ On the other hand, we can conceive a center consisting of four sensory and four motor elements, in which, however, the junctions between the sensory and the motor elements are so imperfect that the nerve-currents meet with much resistance. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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 lower motor center is a group of motor and central neurones, lying anywhere in the cord or brain stem, and capable of directly arousing a certain coördinated muscular movement. One such unit gives flexion of the leg, another gives extension of the leg, a third gives the rapid alternation of flexion and extension that we see in the scratching movement of the dog. Such a motor center can be aroused to activity by a sensory stimulus, and the resulting movement is then called a reflex. ”

“ 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 ”

“ The motor mechanism is that which puts the whole in motion. It either generates its own motive power, like the steam-engine, the caloric engine, the electro-magnetic machine, etc., or it receives its impulse from some already existing natural force, like the water-wheel from a head of water, the windmill from wind, etc. ”

“ 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 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. ”

“ The "weaker and purer" sensory currents furnish "ideas of the environment," while the "motor feelings" only furnish "ideas of the organism." What he means by motor feelings as distinguished from motor impulses following normally upon the discharges of the sensori-motor centers it is difficult to see. He seems to think there can be motor without sensory phenomena, and to forget that all sensory currents, whether peripheral or internal may produce motor effects. ”

“ To the motor system that only which is its equal, and thus the movement of nature, can of necessity become an object. The motor system represented as a sense, cannot, however, perceive the borrowed or derived motion, not the planetary or massive motion, but the primary motion of the æther. The planetary motion is related to the primary motion as the oxydation is to the electrism, as chemical analysis to chemical affinity, and consequently also as respiration to smelling, as digestion to tasting, in short, as the material metatype to the spiritual antetype. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ Modern physiology, from its objective point of view, is engaged over finer and finer issues of microscopic and experimental work; and, from its subjective point of view, is becoming more and more psychological, seeking a higher level of interpretation, and a statement of the departmental life of the brain in terms of ever-increasing complexity. The motor centres, governing the voluntary purposeful movements of the body, are considered to be not simply motor, but “psycho-motor” ”

“ 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. ”

“ 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. ”

“ 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. ”

“ Moving objects exert, as is well known, a peculiar motor stimulation upon the eye, they draw our attention and our look after them. If the look really follows them ... we assume that they move. But if the eye, instead of following the moving objects, remains steadfastly at rest, it must be that the constant stimulus to motion which it receives is neutralized by an equally constant current of innervation flowing into its motor apparatus. ”

“ 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. ”

“ The growing complexity of the nervous system shunts the excitation received on to an ever larger variety of motor mechanisms, and so sketches out simultaneously an ever larger number of possible actions. ”

“ In all the foregoing chapters we have been considering only the muscular engines of the human machine, counting them over and comparing their construction and their mechanism with those of the internal-combustion engine of a motor cycle. But of the levers or crank-pins through which muscular engines exert their power we have said nothing hitherto. Nor shall we get any help by now spending time on the levers of a motor cycle. We have already confessed that they are arranged in a way which is quite different from that which we find in the human machine. ”

“ 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 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. ”

“ Such objects are of value as educational materials to the degree to which they call for necessary muscular adjustments similar to those which the race from the earliest times has experienced. Every sensation or thought, the psychologists affirm, naturally stimulates a motor adjustment which reinforces the original sensory or central impulse which originated the motion. ”