CHAPTER III. 



SMOOTH MUSCLE AND CILIATED CELLS. 

 SMOOTH MUSCLE. 



There are two types of muscle which are independent of volun- 

 tary action, cardiac muscle which is striated and smooth muscle 

 which lacks transverse striations. Smooth muscle fibres are 

 elongated and pointed at both ends. They are generally collected 

 into bundles. These bundles are attached at their ends to the 

 membranous parts where they occur. 



The importance of plain or smooth muscle will be realized when 

 its wide distribution is considered. It is found in the lower half 

 of the gullet, the stomach, and intestines. In the alimentary canal 

 it occurs not only in the muscular coat, but as a layer in the mucous 

 membrane and in the villi. It is present likewise in the trachea, 

 bronchial tubes, bladder, ureters, uterus, glandular ducts, genital 

 organs, spleen, ciliary muscle and iris. The contractile element in 

 blood vessels consists of plain muscle. Thus it is by means of 

 smooth muscle that blood is shifted from one part to another and 

 emergencies are met. This adjustment is controlled largely through 

 the nervous system. 



Movements of the alimentary canal, mixing of the digestive 

 fluids with the food and onward propulsion of the contents, are 

 brought about by smooth muscle. Its function in regulating blood 

 supply and the mechanics of digestion are alone sufficient to 

 demonstrate its necessity in the organism. 



Extensibility and Elasticity. -The extensibility and elas- 

 ticity are similar to those properties in striated muscle. However 

 in the stomach, bladder and uterus the extensibility is much greater. 

 The capacity of these organs depends upon the power of extension, 

 for when empty they are contracted to a small size. 



Irritability. Electrical stimulation is relatively ineffective 



42 



