Muscle Lab

Introduction Jan Swammerdam, who demonstrated that an isolated frog muscle could be made to contract when the sciatic nerve was irritated with a metal object, conducted the first muscle experiments between 1661 and 1665. Later, between 1737-1798 Luigi Galvani determined that frog muscle responded to electrical currents. The kymograph, which was invented in the late 1840’s lead to the revolution of experimental physiology because it enabled muscle contractions to be analyzed and recorded. The muscle cell or fiber is the basic unit of a muscle. The frog gastrocnemius muscle contains many muscle fibers. Each of these fibers has its own threshold and responds all-or-none (twitch) when stimulated. All of the fibers in a muscle do not have the same threshold and when a stimulus is applied to the muscle does not necessarily excite all the fibers in it. The threshold is the intensity of a stimulus, which brings about a response. As the intensity of the stimulus increases above the threshold, more and more fibers are stimulated and the response becomes vast. The strength of the muscle contraction therefore can be increased in two ways: by stimulating existing active motor units and by increasing the number of active motor units. The force that a muscle can generate is dependent upon the total number of muscle fibers. So muscles with small cross-sectional areas are not able to generate large forces as those with large cross-sectional areas. Muscle fibers cannot continually lift. After a short time, the muscle will lose its ability to shorten and will ultimately fail. Due to the accumulation of waste products and the depletion of stored energy materials, a muscle is said to have lost its contractility and become fatigued. Eventually, stimulus intensity is reached beyond which the response is constant. When this occurs the stimulus is called the maximal stimulus mark, which is the point where all fibers in the muscle are stimulated and responding all-or-none. The frog muscle is used in this laboratory exercise in place of mammalian muscle because of its tolerance to temperature change and handling. The objective in this experiment is to recorded the twitch threshold, maximal twitch response, summation, fatigue for frog skeletal muscle and its motor nerve and tetanus

Method The hardware was connected as seen in figure 1 and the MP30 and the BSLSTM stimulator were turned on. The stimulator settings were established by turning the level knob counterclockwise until it stopped at 0 volts. The key was then turned to the right to set the Range at 10V. Next, the reference switch was flipped and fixed to 15ms. The BSL PRO software was launched on the host computer and a new file was created. To ensure the stimulator was working, the On/Off button was used to turn the stimulator ON. The Pulse light was checked to ensure it was blinking on the front of the BSLSTM.

Figure 1: shows the simulator setup

Calibration Channel 1 was brought up, while the controls on the BSL Stimulator was set to a level of 0 Volts the Cal 1 button was clicked in the Scaling window. The Cal 1 Input Value now reflected the actual reading on Channel 1. The Cal 2 Input Value was determined then manually entered. Channel 2 was brought up in the scaling window, while only the S-hook was attached to the SS12LA Force Transducer; the Cal 1 button was clicked. The 50-gram weight was attached to the S-hook and the Cal 2 button clicked was clicked and the setup window closed.

Results:
Sciatic Nerve 1st Leg and 2nd Leg

Figure 2: shows the response of the sciatic nerve in the first leg and second leg.

12.66Hz at summation
Fatigue: 24.39 Hz
Tetanus: 59 seconds

Figure 3: shows the graph that was used to assess the summation, fatigue, tetanus and threshold of the first leg.

Sciatic Nerve 2nd Leg

Discussion:

Works Cited

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