Rhythmic movements : a contribution to the physiology of the central nervous system

Abstract

Of all the dynamic activities which are evidenced throughout the animal Kingdom there is none so wide-spread nor is there any so fundamental as the act of rhythmic movement.ythmic movement. Such functions are present. everywhere - from the pulsating vacuole of the unicellular organism to the heating mammalian heart - and they may persist in action through the whole existence of the organism, from the beginning of life to its end.In the higher metazoa there are rhythmic functions some of which are continually in progress and the commencement and termination of which are coterminous with the boundaries of life. Such are the rhythmic movements of the intestine, of the heart and blood vessels, and of the act of respiration. These may progress throughout.life without interruption. But some of them may be interrupted for shorter or for longer durations of time. To them may be added other rhythmic functions -.the rhythmic reflexes so-called - which are evidenced in short; periods of activity. Of these rhythmic,reflexes the scratch-reflex is one of the most common occurrence, and another is that rhythmic act of progression to the elucidation of some properties of which this thesis is devoted.These great rhythmic activites - cf the intestinal tract, cf the vascular mechanism, of respiration, and of progression - are conditioned in different degress by the central and by the autonomics nervous systems; and they may be arranged in a series the order of which is determined by the relative importance of the central nervous factor. This series corresponds to another possible one in which the rhythmic functions are arranged in accordance with the morphological characteristics of the tissue the movements of which express the rhythmic activity.Sherrington has pointed out (19, p.312) that although a diffuse nervous system seems to be the only one in such invertebrates as Medusa, in the. higher animals another - the "synaptic" - is developed. This system co-exists with the diffuse and in various places dominates it. Even in the highest mammals the autonomic system of the viscera, of the heart, and of the blood-vessels remains diffuse.When attempting to arrange the rhythmic activities in an ordered series we may commence with those of the hollow viscera - the intestines and the heart - which are least controlled by the central nervous system. In the case of the intestines the musculature is of the visceral type and the control of the central nervous system is perhaps at its lowest. The musculature of the heart'is in closer approximation to that of the skeletal muscles, and the rhythmic mechanism is more under control than is that of the intestines.Next in order may he placed the rhythmic act of respiration. The contractile tissue is here of the skeletal type, and the nervous mechanism is one of the central nervous system - synaptic. The act proceeds rhythmically and continuously, but it may be stopped for a short time by the activity of inhibitory centres. It may be remarked here that although in the mammal the skeletal muscle is- the chief contractile tissue involved in the act, in lower vertebrates, such as the frog, there is in addition to the activity of the skeletal musculature of the mouth and throat and (in dyspnoea) of the flanks, an activity of a sheet of visceral muscle which covers the lungs and is a factor in the movements of the lungs themselves, (Kahn, II.; Francois-Pranck, 17, 13.)Finally we may place the rhythmic reflexes. These are again completely conditioned by the influence of the activity of the synaptic central nervous system upon an arrangement of skeletal muscles. But the acts are more under the influence of the higher centres. In the case of the scratchreflex this is probably less so than in the case of the rhythmic act of progression.We may say that there are two main types of rhythmic activity in the mammal. These are conditioned by the activity, on the one hand, of a diffuse nervous system and, on the other hand, of a synaptic nervous system. As an example of the latter we may take the act of respiration, and it the chief aim of this thesis to shew the close similarity thereto.of the rhythmic act of progression.