The Muscles : Part 1

Hygienic Physiology: with Special Reference to the Use of Alcoholic Drinks and Narcotics
by Joel Dorman Steele, Ph.D.

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"Behold the outward moving frame, Its living marbles jointed strong With glistening band and silvery thong, And link'd to reason's guiding reins By myriad rings in trembling chains, Each graven with the threaded zone Which claims it as the Master's own."

Analysis of the Muscles

The Use of the Muscles. - The skeleton is the image of death. Its unsightly appearance instinctively repels us. We have seen, however, what uses it sub serves in the body, and how the ugly-looking bones abound in nice contrivances and ingenious workmanship. In life, the framework is hidden by the flesh. This covering is a mass of muscles, which by their arrangement and their properties not only give form and symmetry to the body, but also produce its varied movements.

In Fig. 14, we see the large exterior muscles. Beneath these are many others; while deeply hidden within are tiny, delicate ones, too small to be seen with the naked eye. There are, in all, about five hundred, each having its special use, and all working in exquisite harmony and perfection.

Contractility. - The peculiar property of the muscles is their power of contraction, whereby they decrease in length and increase in thickness. This may be caused by an effort of the will, by cold, by a sharp blow, etc. It does not cease at death, but, in certain cold-blooded animals, a contraction of the muscles is often noticed long after the head has been cut off.

Arrangement of the Muscles. - The muscles are nearly all arranged in pairs, each with its antagonist, so that, as they contract and expand alternately, the bone to which they are attached is moved to and fro.

If you grasp the arm tightly with your hand just above the elbow joint, and bend the forearm, you will feel the muscle on the inside swell, and become hard and prominent, while the outside muscle will be relaxed. Now straighten the arm, and the swelling and hardness of the inside muscle will vanish, while the outside one will, in turn, become rigid. So, also, if you clasp the arm just below the elbow, and then open and shut the fingers, you can feel the alternate expanding and relaxing of the muscles on opposite sides of the arms.

If the muscles on one side of the face become palsied, those on the other side will draw the mouth that way. Squinting is caused by one of the straight muscles of the eye contracting more strongly than its antagonist.

Kinds of Muscles. - There are two kinds of muscles, the voluntary, which are under the control of our will, and the involuntary, which are not. Therefore our limbs stiffen or relax as we please, but the heart beats on by day and by night. The eyelid, however, is both voluntary and involuntary, so that while we wink constantly without effort, we can, to a certain extent, restrain or control the motion.

Structure of the Muscles. - If we take a piece of lean beef and wash out the red color, we can easily detect the fine fibers of which the meat is composed. In boiling corned beef for the table, the fibers often separate, owing to the dissolving of the delicate tissue which bound them together. By means of the microscope, we find that these fibers are made up of minute filaments (fibrils), and that each fibril is composed of a row of small cells arranged like a string of beads. This gives the muscles a peculiar striped (striated) appearance. The cells are filled with a fluid or semi fluid mass of living matter.

The binding of so many threads into one bundle confers great strength, according to a mechanical principle that we see exemplified in suspension bridges, where the weight is sustained, not by bars of iron, but by small wires twisted into massive ropes.

The Tendons. - The ends of the muscles are generally attached to the bone by strong, flexible, but inelastic tendons. The muscular fibers spring from the sides of the tendon, so that more of them can act upon the bone than if they went directly to it. Besides, the small, insensible tendon can better bear the exposure of passing over a joint, and be more easily lodged in some protecting groove, than the broad, sensitive muscle. This mode of attachment gives to the limbs strength, and elegance of form. therefore, for example, if the large muscles of the arm extended to the hand, they would make it bulky and clumsy. The tendons, however, reach only to the wrist, whence fine cords pass to the fingers.

Here we notice two other admirable arrangements. 1. If the long tendons at the wrist on contracting should rise, projections would be made an. Therefore the beauty of the slender joint be marred. To prevent this, a stout band or bracelet of ligament holds them down to their place. 2. In order to allow the tendon which moves the last joint of the finger to pass through, the tendon which moves the second joint divides at its attachment to the bone. This is the most economical mode of packing the muscles, as any other practicable arrangement would increase the bulk of the slender finger.

Since the tendon can not always pull in the direction of the desired motion, some contrivance is necessary to meet the want. The tendon (B) belonging to one of the muscles of the eye, for example, passes through a ring of cartilage, an. Therefore a rotary motion is secured.

The Levers of the Body. In producing the motions of the body, the muscles use the bones as levers. We see an illustration of the first class of levers in the movements of the head. The back or front of the head is the weight to be lifted, the backbone is the fulcrum on which the lever turns, and the muscles at the back or front of the neck exert the power by which we toss or bow the head.

When we raise the body on tiptoe, we have an instance of the second class. Here, our toes resting on the ground form the fulcrum the muscles of the calf acting through the tendon of the heel, are the power and the weight is borne by the ankle joint.

An illustration of the third class is found in lifting the hand from the elbow. The hand is the weight, the elbow the fulcrum, and the power is applied by the biceps muscle at its attachment to the radius In this form of the lever there is great loss of force, because it is applied at such a distance from the weight, but there is a gain of velocity, since the hand moves so far by such a slight contraction of the muscle. The hand is required to perform quick motions, and therefore this mode of attachment is desirable.