The Muscular System : Part 5

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 19 of 27)

Practical Work

The reddish muscle found in a piece of beef is a good example of striated muscle. The clear ring surrounding the intestine of a cat (shown by cross section) and the outer portion of the preparation from the cow's stomach, sold at the butcher shop under the name of tripe, are good examples of non-striated muscular tissue. The heart of any animal, of course, shows the heart muscle.

To show the Structure of Striated Muscle. - Boil a tough piece of beef, as a cut from the neck, until the connective tissue has thoroughly softened. Then with some pointed instrument, separate the main piece into its fiber bundles and these in turn into their smallest divisions. The smallest divisions obtainable are the muscle cells or fibers.

To show Striated Fibers. - Place a small muscle from the leg of a frog in a fifty-per-cent solution of alcohol and leave it there for half a day or longer. Then cover with water on a glass slide, and with a couple of fine needles tease out the small muscle threads. Protect with a cover glass and examine with a microscope, first with a low and then with a high power. The striations, sarcolemma, and sometimes the nuclei and nerve plates, may be distinguished in such a preparation.

To show Non-striated Cells. - Place a clean section of the small intestine of a cat in a mixture of one part of nitric acid and four parts of water and leave for four or five hours. Thoroughly wash out the acid with water and separate the muscular layer from the mucous membrane. Cover a small portion of the muscle with water on a glass slide and tease out, with needles, until it is as finely divided as possible. Examine with a microscope, first with a low and then with a high power. The cells appear as very fine, spindle-shaped bodies.

To illustrate Muscular Stimulus and Contraction. - Separate the muscles at the back of the thigh of a frog which has just been killed and draw the large sciatic nerve to the surface. Cut this as high up as possible and, with a sharp knife and a small pair of scissors, dissect it out to the knee. Now cut out entirely the large muscle of the calf of the leg but leave attached to it the nerve, the lower tendon, and the bones of the knee. Mount on an upright support, as shown in Fig. 120, and fasten the tendon to a lever below by a thread or small wire hook:

1. Lay the nerve over the ends of the wires from a small battery which are attached to the support at A, and arrange a second break in the circuit at B. At this place the battery circuit is made and broken either by a telegraph key or by simply touching and separating the wires. Note that the muscle gives a single contraction, or twitch, both when the current is made and when it is broken.

2. Remove the current and pinch the end of the nerve, noting the result. With very fine wires, connect the battery directly to the ends of the muscle. Stimulate by making and breaking the current as before. In this experiment the muscle cells are stimulated by the direct action of the current and not by the current acting on the nerve.

3. With the wires attached to either the muscle or the nerve, make and break the current in rapid succession. This causes the muscle to enter into a second contraction before it has relaxed from the first, and if the shocks follow in rapid succession, to continue in the contracted state. This condition, which represents the method of contraction of the muscles in the body, is called tetanus.

Note. - In these experiments a twitching of the muscle is frequently observed when no stimulus is being applied. This is due to the drying out of the nerve and is prevented by keeping it wet with a physiological salt solution.

To show the Action of Levers. - With a light but stiff wooden bar, a spring balance, and a wedge-shaped fulcrum, show:

1. The position of the weight, the fulcrum, and the power in the different classes of levers, and also the weight-arm and the power-arm in each case.

2. The direction moved by the power and the weight respectively in the use of the different classes of levers.

3. That when the power-arm and weight-arm are equal, the power equals the weight and moves through the same distance.

4. That when the power-arm is longer than the weight-arm, the weight is greater, but moves through a shorter distance than the power.

5. That when the weight-arm is longer than the power-arm, the power is greater and moves through a shorter distance than the weight.

To show the Loss of Power in the Use of the Body Levers. - Construct a frame similar to, but larger than, that shown in Fig. 120, (about 12 inches high), and hang a small spring balance (250 grams capacity) at the place where the muscle is attached. Fasten the end of a lever to the upright piece, at a point on a level with the end of the balance hook. (The nail or screw used for this purpose must pass loosely through the lever, and serve as a pivot upon which it can turn.) The lever should consist of a light piece of wood, and should have a length at least three times as great as the distance from the hook to the turning point. Connect the balance hook with the lever by a thread or string, and then hang upon it a small body of known weight. Note the amount of force exerted at the balance in order to support the weight at different places on the lever. At what point is the force just equal to the weight? Where is it twice as great? Where three times? Show that the force required to support the weight increases proportionally as the weight-arm and as the distance through which the weight may be moved by the lever. Apply to the action of the biceps muscle in lifting weights on the forearm.

A Study of the Action of the Biceps Muscle. - Place the fingers upon the tendon of the biceps where it connects with the radius of the forearm. With the forearm resting upon the table, note that the tendon is somewhat loose and flaccid, but that with the slightest effort to raise the forearm it quickly tightens. Now transfer the fingers to the body of the muscle, and sweep the forearm through two or three complete movements, noting the changes in the length and thickness of the muscle. Lay the forearm again on the table, back of hand down, and place a heavy weight (a flatiron or a hammer) upon the hand. Note the effort required to raise the weight, and then shift it along the arm. Observe that the nearer it approaches the elbow the lighter it seems. Account for the difference in the effort required to raise the weight at different places. Does the effort vary as the distance from the tendon?

D.C. Heath and Co. - Publishers
Original copyright 1909