This experimental method was obtained from the official website of the Fourth Military Medical University
Operation method
Mechanical analysis of skeletal muscle contraction experiment
Principle
Muscle, nerve and gland tissues are called excitable tissues, and their excitability is large, and the excitability of different tissues and cells is not the same, and the excitability of muscle tissues is mainly manifested as contractile activities. Stimulation (stimulation) to make the excitable tissues excited, it is necessary to achieve a certain amount of stimulation, that is, the stimulation intensity, stimulation time and intensity - time rate of change must reach a certain value. By fixing the latter two conditions, changing the stimulus intensity, recording and measuring the muscle contraction tension, you can determine the muscle tissue just occurred in the excitement of the stimulus known as the threshold stimulus (threshold stimulus), the intensity of the threshold stimulus known as the threshold strength (threshold strength). With the increase of the stimulus strength, the muscle contraction tension also increases accordingly, the stimulus strength is greater than the threshold stimulus is called suprathreshold stimulus (suprathreshold stimulus), can cause the organization to produce the maximum excitation of the smallest stimulus is called the maximum stimulus (maximal stimulus). When a whole skeletal muscle or a single muscle cell is stimulated by a threshold or suprathreshold stimulus, an action potential occurs first, followed by a contraction, which is called a single twitch. The whole process of contraction can be divided into two periods: systole and diastole, with the former having a shorter duration than the latter. If the muscle is stimulated with continuous pulses, the form of muscle contraction will vary with the frequency of the stimulus. At a low frequency of stimulation, the single contraction process (including the diastolic period) induced by the previous stimulus is over by the time each new stimulus arrives, so that each stimulus induces a separate single contraction. When the frequency of stimulation increases to a certain limit, the subsequent stimulus may appear before the end of the diastolic phase of the previous contraction, so the muscle in the incomplete diastole (itself is still in a certain degree of shortening or tension exists) on the basis of a new contraction, which occurs in the contraction process of the composite, so that continuous, the muscle will be manifested in the incomplete contraction of the tonic (incomplete) tetanus), which is characterized by each new contraction appears in the diastolic process of the previous contraction, forming a sawtooth shape on the tracing curve; if the frequency of stimulation continues to increase, the muscle may start a new contraction before the end of the systolic phase of the previous contraction or at the apex of the systolic phase, and then the changes in tension or length of each contraction can be fused and superimposed, so that the jaggedness of the tracing curve disappears, this is the complete tetanus (cetanus). This is complete tetanus.
Materials and Instruments
Frogs Toads Move I. Preparation of frog sciatic nerve gastrocnemius muscle specimens (3) Observation recording. Click the "Stimulation" button, select the minimum stimulus intensity (0.1V), and then gradually increase the stimulus intensity to record the threshold stimulus and maximum stimulus value. Figure 1 Caveat 1. After each stimulation to cause muscle contraction must be separated by a certain time (0.5 ~ 1min), and commonly used Ren's fluid to wet the specimen to ensure muscle excitability. 2. The frequency of stimulation should be gradually increased from low, and the duration of stimulation at each frequency should not be too long. 3. If muscle contracture occurs without giving stimulation, the instrument grounding should be checked to see if it is good, and if necessary, a ground wire can be connected to the muscle groove or the iron column frame. For more product details, please visit Aladdin Scientific website.
Ren's Liquid BL-420 Bio-signal Acquisition and Processing System Frog Surgical Instruments Muscle Groove Tension Transducer Iron Column Stand Double Concave Clamps
Connecting the experimental apparatus
The sciatic nerve gastrocnemius muscle specimen was fixed in the muscle groove, the femoral stump was fixed in the small hole of the muscle groove, the Achilles tendon of the gastrocnemius muscle was tied to the focus point of the suspension beam of the tension transducer through the ligature, the transducer was fixed in the double-concave clamps of the iron column frame, and was connected to the input channel jack of the biosignal acquisition and processing system. The sciatic nerve is placed on the stimulating electrode of the muscle groove, and the stimulating electrode is connected to the stimulating output jack.
III. Experimental Observation Items
1. The effect of stimulation intensity on skeletal muscle contraction tension.
(1) Move the biconcave clamp and tighten the ligature wire.
(2) Stimulation parameter settings. Single-shot mode, wave width 0.1-0.3ms.
(4) Measure the muscle contraction tension corresponding to each stimulus intensity; measure the duration of the systolic and diastolic phases of the muscle during the maximal stimulus, and compare the difference between the two (Fig. 1).
2. Effect of stimulus frequency on the form of skeletal muscle contraction.
(1) Choose a continuous single stimulus with a wave width of 0.3 to 0.5 ms, maximum stimulus intensity, and a stimulus interval greater than the time course of muscle contraction, and record the single contraction tension curve of the muscle.
(2) Choose double stimulation (the rest of the stimulation parameters remain unchanged), change the stimulation wave interval so that the stimulation interval time is smaller than the muscle single-contraction time interval and longer than the systole time, and record the composite curve of the two contractions.
(3) Choose continuous stimulation, the rest of the stimulation parameters remain unchanged, adjust the stimulation frequency from low to high, and record the tension curves of incomplete tonic contraction and complete tonic contraction of the muscle (Figure 2).
Figure 2