CHAPTER VII. 

 GENERAL PHYSIOLOGY OF MUSCLE -TISSUE. 



The Muscle-tissue. The muscle-tissue, which closely invests the 

 bones of the body and which is familiar to all as the flesh of animals, is the 

 immediate cause of the active movements of the body. This tissue is grouped 

 in masses of varying size and shape, which are technically known as muscles. 

 The majority of the muscles of the body are connected with the bones of the 

 skeleton in such a manner that, by an alteration in their form, they can 

 change not only the position of the bones with reference to one another, but 

 can also change the individual's relation to surrounding objects. They are 

 therefore, the active organs of both motion and locomotion, in contradistinc- 

 tion to the bones and joints, which are but passive agents in the performance 

 of the corresponding movements. In addition to the muscle masses which 

 are attached to the skeleton, there are also other collections of muscle- 

 tissue surrounding cavities such as the stomach, intestine, blood-vessels, etc., 

 which impart to their walls motility, and so influence the passage of material 

 through them. 



Muscles produce movement of the structures to which they are attached 

 by the property with which they are endowed of changing their shape, 

 shortening or contracting under the influence of a stimulus transmitted to 

 them from the nerve system. Muscles are divided into: 



1. Voluntary muscles, comprising those the activity of which is called 



forth by an act or effort of volition. 



2. Involuntary muscles, comprising those the activity of which is entirely 

 independent of the volition. 



The voluntary muscles are also known from their attachment to the 

 skeleton as skeletal, and from their microscopic appearance as striped or 

 striated muscles. Though for the most part these muscles are red, there 

 are certain muscles in man and other animals which are pale in color and 

 in many muscles pale fibers are extensively distributed among the red fibers. 

 The involuntary muscles, from their relation to the viscera of the body, are 

 known also as visceral, and from their microscopic appearance as plain, 

 smooth, or non-striated muscles. 



THE VOLUNTARY OR SKELETAL MUSCLE. 



All skeletal muscles consist of a central fleshy portion, the body or belly, 

 provided at either extremity with a tendon in the form of a cord or mem- 

 brane. The body is the active, contractile region, the source of the move- 

 ment; the tendon is the inactive region, the passive transmitter of the move- 

 ment to the bones. 



A skeletal muscle is a complex organ consisting of a framework of 

 connective tissue, supporting muscle-fibers, blood-vessels, nerves, and 



48 



