The experimental method was obtained from the official website of the Fourth Military Medical University
Operation method
Effect of load on muscle contraction
Principle
The negative abutment applied to a muscle before it contracts is the preload. Preload can change the initial length of the muscle before contraction, within a certain paradigm. The longer the initial length, the greater the amplitude of muscle contraction, so that the muscle reaches the optimal initial length of the preload for the optimal preload. The load encountered after the beginning of muscle contraction is called afterload; within a certain range, with the increase of afterload, the muscle contraction tension increases, and the shortening speed and amplitude decreases; when the afterload increases to a certain value, the muscle tension reaches the maximum, but the muscle can't be shortened, and the work done is zero, in the appropriate afterload conditions, the muscle can do the maximum work.
Materials and Instruments
Toad or frog Move I. The effect of preload on muscle contraction 1. Preparation of sciatic nerve and intestinal muscle specimen: Referring to the method of preparing sciatic nerve specimen in the guided experiment of action potential of sciatic nerve trunk, isolate the sciatic nerve to the slapped fossa, hitch the sciatic nerve to the gastrocnemius muscle, cut off all the thigh muscles around the knee joint and scrape the femur clean with ordinary scissors, then cut off the middle part of the femur, retaining the lower part of the femur for about 1 centimeter. The Achilles tendon was cut and the gastrocnemius muscle was freed to the knee joint, and then the rest of the calf was cut off with the knee capsule. A small hole is made in the Achilles tendon with a probe and set aside. The sciatic nerve is gently touched with a zinc-copper bow moistened with Ren's solution. If the gastrocnemius muscle contracts rapidly and markedly, the specimen is excitable and can be placed in a Petri dish containing Ren's solution. Caveat I. During the experiment, the initial length of the screw and the stimulation parameters were kept unchanged.The next stimulus was applied at the same interval (0.5-1 min) to ensure that the muscles had the same rest time, and Ren's solution was added to protect the specimen. For more product details, please visit Aladdin Scientific website.
Ren's solution
Notated drum, myotome Electromagnetic marker, universal support table, electrical stimulator, frog surgical instruments, straightedge, petri dish
2. Fix the sciatic nerve specimen in the actuator. Screw the rear loading screw away from the tracing lever, adjust the initial length screw so that the lever is in a horizontal position, adjust the tracing pen so that the tip of the pen is tangential to the drum surface of the marking pattern.
3. Choose suitable stimulation conditions. The wave width is about 0.5ms. Stimulate the sciatic nerve with a single pulse of maximum (or medium) stimulation intensity, the muscle contraction can be seen once, and the first linear curve is drawn on the striated drum, and the striated drum is rotated by hand for about 1cm, and then add 10g of weights under the lever, stimulate it once more, and then a linear curve is drawn, and then rotate the drum once again, and then add weights one after another in the same way as above, until the striated drum is no longer in the horizontal position. Until the muscles no longer contract.
4. Processing and calculating the results of the experiment Measure the height H of each contraction with a ruler, and trace the length L of the lever (from the fulcrum to the tip of the pen) and the distance l (from the fulcrum to the hanging weights). Calculate the actual height h to which the weight is lifted and the work done by the muscle according to the principle of proportionality of the sides of similar triangles (see the figure); fill in Table (3-1) and graph it on coordinate paper (use the horizontal coordinate to indicate the weight of the weight, i.e., the weight of the load, and the vertical coordinate to indicate the work done, and note the optimum front load for this experiment).
Two similar triangles: HLL is the large triangle and hll is the small triangle. H is the contracted height of the stroke on the drum; L is the length of the traced lever and L is the position of the lever when the muscle is contracted; l is the distance from the axis of rotation to the hammer, and h is the height to which the hammer is actually raised.
Units of measure: Length: cm Weight: g
Work done by muscle contraction = weight of weight W(g) x actual height of weight lifted h(cm) = Wx lH/L (g.cm).
If the resulting value is multiplied by 981, it is the work expressed in ergs (Erg).
II Effect of afterload on muscle contraction
A specimen of sciatic nerve a gastrocnemius muscle with good excitability was fixed in the actuator. The after-loading screw of the actuator lever is rotated upward against the lever to ensure that the muscle is loaded only after the beginning of contraction. Experimental method.
Calculate the work done by the muscle under the condition of after-loading in the same way as described above, and fill in Table (3-1), and indicate it by drawing on coordinate paper. Note the optimum afterload.
