Nutritional physiology / by Percy Goldthwait Stiles.

  • Stiles, Percy Goldthwait, 1875-1936.
Date:
1931
Catalogue details

Licence: In copyright

Credit: Nutritional physiology / by Percy Goldthwait Stiles. Source: Wellcome Collection.

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    CHAPTER IV THE WORK OF MUSCLES AND GLANDS We cannot enter upon a description of the alimentary canal and its activities until we have devoted some space to the physiology of contraction and secretion. Movement is the most familiar manifestation of animal life. When visible to the naked eye it is the expression of the shorten- ing of elongated units—cells or fibers—associated to form contractile tissues. In the human body there are three principal kinds of these tissues. The obvious external movements of the limbs and the features, the act of breathing, etc., are produced by what we call the skeletal muscles. Contractile tissue of another order forms the walls of the heart and furnishes the power for its beating. A third kind occurs in the walls of the alimentary tract, in the blood-vessels, and elsewhere. The term skeletal applied to a type of contractile tissue implies relationship to the bones. It is easy to see that external movements are made effective through the connec- tion of the muscles which produce them with bones acting as levers. In some instances the term is a misnomer, for there are some small muscles histologically like the rest which do not act upon bones. The large and conspicuous muscles are attached, usually at both ends, to the bones. We can generally observe that one end is more freely mov- able than the other. The comparatively fixed end is called the origin of the muscle, the end more subject to move- ment is its insertion. Whab is called a skeletal muscle is a bundle in which we can distinguish an active and a passive part. There are the true contractile elements and there is the connective tissue. The inactive substance forms a sheath enclosing the rest and also partitions which subdivide the interior.