Experiments on the relationship between load and skeletal muscle contraction
Experiments on the relationship between load and skeletal muscle contraction
This experimental method was obtained from the official website of the Fourth Military Medical University
Operation method
Experiments on the relationship between load and skeletal muscle contraction
Principle
The performance of contraction is characterized by the amount of force and/or shortening that occurs during contraction, as well as the velocity at which tension or shortening occurs. If the length of the muscle remains unchanged during contraction and only the tension increases, then this form of contraction is called isometric contraction (isometric contraction); contraction only occurs when the muscle shortens and the tension remains unchanged, called isotonic contraction (isotonic contraction). The load that the muscle undergoes before contraction is called preload (preload), which gives the muscle a certain initial length. The resistance encountered by the muscle during contraction is called afterload, which causes the muscle to contract with a corresponding tension. Within certain limits, muscle contraction can be intensified with an increase in preload. If the preload is too large, it will lead to the weakening of the muscle contraction force; the larger the afterload, the larger the tension generated during muscle contraction, the later the start of the shortening time, the slower the shortening speed and the smaller the shortening amplitude. When the load reaches a certain value, it can lead to a muscle contraction that produces only tension, while the length remains unchanged (isometric contraction).
Materials and Instruments
Ren's Liquid BL-420 Bio-signal Acquisition and Processing System Frog Surgical Instruments Muscle Groove Tension Transducer Iron Column Stand Double Concave Clamp Suspendable Small Weights Circular Gauge Straight Ruler Move I. Preparation of frog sciatic nerve gastrocnemius muscle specimens Caveat 1. the wire on the gastrocnemius tendon must be tied tightly and securely to prevent slipping due to excessive loading. 2. A single maximal stimulus should be used, and other stimulus parameters should not be changed arbitrarily in the same set of experiments. 3. Before changing the load for stimulation, the muscle should be fully relaxed and rested for 1~2min, and the muscle should be rinsed with Ren's solution to prevent drying of the specimen. For more product details, please visit Aladdin Scientific website.
Fix the specimen in the muscle groove
III. Experimental Observation Program
1. The effect of constant afterload and varying preload on skeletal muscle contraction.
(1) Start the biosignal acquisition and processing system and enter the experimental state.
(2) Firstly, screw the screw on the lower side of the horizontal lever of the muscle groove, because the lever is supported by the top of the screw, so the length of the muscle before contraction remains unchanged, and then hang 100g weights at the appropriate position on the horizontal lever (1cm from the pivot point), stimulate the sciatic nerve with a single maximum stimulus intensity, and record the contraction curve of the gastrocnemius muscle, the muscle contraction of this time, the preload of the muscle contraction is 0g, and the afterload of the muscle contraction is 100g.
(3) Turn down the screw on the lower side of the horizontal lever of the muscle groove so that it leaves the lever, and hang a 10g weight (i.e., preload) at the same appropriate position on the horizontal lever. Then, the screw was rotated upward until it was just against the lever, and then a 90g weight was added to the 10g weight, and the sciatic nerve was stimulated with a single maximum stimulus intensity, and the gastrocnemius muscle contraction curve was recorded, at which time the afterload of muscle contraction was still 100g.
(4) Change the preload (initial length) of the muscle to 20g, 30g, 40g, 50g, 60g, 70g, 80g, 90g, 100g, and the afterload to 100g as described above, and record the contraction curve of the muscle.
(5) Calculate the mechanical work of the skeletal muscle at different preloads and fill in the table below to plot the curve of muscle preload versus muscle work. Measure the height H' of the curve recorded by moving the lever up by 1 cm at the weight connection of the lever, and use this as a calibration value. Muscle work = weight of load applied (W) x distance moved (i.e. raised) by the load (h). h can be calculated by dividing the height of the contraction curve, H, by H', the height of the curve when the load is moved 1 cm. That is, muscle work (g-cm) = weight of load applied (W) × (H/H').
2. The effect of changing the afterload on the contraction of skeletal muscle by keeping the preload constant.
(1) Stimulate the sciatic nerve with a single maximum stimulus intensity and record the contraction curve of the gastrocnemius muscle. The preload and afterload of the muscle contraction at this time were both zero.
(2) Suspend a 10g weight at the appropriate position of a horizontal lever in the muscle groove and turn down the screw on the lower side of the lever to move it away from the lever, so that the muscle is elongated, and this initial length is always maintained thereafter. The sciatic nerve was stimulated with a single maximum stimulus intensity, and the contraction curve of the gastrocnemius muscle was recorded, at which time the muscle contracted with a preload of 10 g and an afterload of 10 g as well.
(3) Rotate the screw upward so that it just holds the lever to keep the initial length of the muscle unchanged, then add 10 g to the original 10 g load, stimulate the sciatic nerve, and record the contraction curve of the muscle, at which time the preload of contraction is still 10 g, and the postload is increased to 20 g.
(4) According to the above method, the weight of the preload (initial length) of the muscle was not changed, while the afterload was gradually increased to 30g, 40g, 50g, 60g, 70g, 80g, 90g, 100g, and the contraction curve of the muscle was recorded.
(5) Calculate the mechanical work of the skeletal muscle at different afterloads and fill in the table below to plot the curve of muscle afterload in relation to the work done by the muscle.