CHAPTER XIII 

 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



SECTION I. PRELIMINARY OBSERVATIONS PHYSICAL AND 

 TECHNICAL DATA. 



IN all the great functions of the body muscular movements play 

 an essential part. The circulation and the respiration, the two 

 functions most immediately essential to life, are kept up by the 

 contraction and relaxation of muscles. The movements of the 

 digestive canal, the regulation of the blood-supply to its glands and 

 to all parts of the body, and that immense class of movements 

 which we call voluntary, are all dependent upon muscular action, 

 which, again, is indebted for its initiation, continuance, or control, 

 to impulses passing along the nerves from the nerve-centres. 

 Hitherto we have not gone below the surface fact, that muscular 

 fibres have the power of contracting, either automatically, or in 

 response to suitable stimuli. In this chapter and the two next we 

 shall consider in detail the general properties of muscle, nerve, and 

 the other excitable tissues. 



Lying deeper than the peculiarities of individual muscles, muscular 

 tissue has certain common properties physical, chemical, and 

 physiological. The biceps muscle flexes the arm upon the elbow, 

 and the triceps extends it. The external rectus rotates the eyeball 

 outwards. The intercostal muscles elevate the ribs. The sphincter 

 ani seals up by a ring-like contraction the lower end of the alimentary 

 canal. These actions are very different, but the muscles that carry 

 them out are at bottom very similar. And it cannot be doubted 

 that the functional differences are due entirely, or almost entirely, 

 to differences of anatomical connection, on the one hand with bones 

 and tendons, on the other with the nerve-cells of the spinal cord and 

 brain. The common properties in which all the skeletal muscles 

 agree are the subject-matter of the general physiology of striated 

 muscle. 



The cardiac muscle differs more, both in structure and in function, 

 from the skeletal muscles than these do among themselves; the 

 smooth muscle of the intestines and bloodvessels still more. But 

 every muscular fibre, striped or unstriped, resembles every other 



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