Amphibian Muscle Experiments Lecture Notes

Apparatus and Preparation

• Apparatus Required: Basic Setup

  • Rectangular Myograph board with box
  • Myograph stand
  • Isotonic lever with long and short arms (longer arm acts as stylus)
  • Needles and thread for hooking the tendon
  • Step-down transformer (220V AC to 2-6V DC)
  • Induction coil or student stimulator
  • Smoked drum for recording graphs

• Muscle Preparation

  • Use the Gastrocnemius muscle with knee joint for in vitro experiments
  • Hang the preparation using a piece of thread and knee joint as support
  • Connect the long tendon to the isotonic lever without touching the muscle
  • Ensure knee joint is pinned and muscle set correctly (preloaded vs. afterloaded)

Primary and Secondary Circuits

• Primary Circuit

  • 220V AC transformed to 2-6V DC
  • Connected to primary circuit screws and then to contact blocks

• Secondary Circuit

  • Receives induced current from primary circuit
  • Stimulates the muscle preparation
  • Can deliver single or multiple stimuli using student stimulator

Graph Recording and Analysis

• Recording Setup

  • Smoked drum rotation speed: 64mm/sec
  • Baseline tracing with tuning fork for time marking (100 Hz, 0.1 sec per peak)
  • Single stimulus applied for recording simple muscle twitch

• Simple Muscle Twitch Graph

  • Parts of the graph
    • Point A: Stimulation
    • Point B: Contraction starts
    • Point C: Midpoint
    • Point D: Relaxation starts
    • AB: Latent period
    • BC: Contraction period
    • CD: Relaxation period
    • CE: Height of contraction
  • Graph shows muscle twitch with key points marked
  • Difference in preloaded vs. afterloaded setups
    • Preloaded: physiological curves below baseline, higher contraction height
    • Afterloaded: no physiological curve, lower contraction height

Multiple Stimuli and Fatigue

• Fatigue Curve

  • Application of multiple stimuli at regular intervals
  • Gradual increase in latent period and decrease in contraction height
  • Latent period shortening and height increase due to beneficial effects (increased temperature, calcium availability)
  • Later, contraction height decreases, latent period increases, muscle remains contracted (contraction remainder)

• Contraction Remainder

  • Muscle remains in contracted state, not returning to baseline
  • Caused by ATP loss, calcium not pumped back into sarcoplasmic reticulum
  • Reversible by resting muscle and applying fresh saline

Effects of Temperature

• Effect of Hot and Cold Saline
  • Normal curve vs. heated saline (up to 40°C)
    • Latent period shortens, contraction height increases (beneficial effect)
  • Cold saline application
    • Latent period increases, contraction height decreases
  • Graphs show temperature effects on muscle contraction

Two Successive Stimuli

• Summation and Tetany
  • First contraction followed by second stimulus during latent period shows no new contraction
  • Second stimulus during contraction period shows summation (increased contraction height)
  • Second stimulus during relaxation shows second contraction, with greater height than first

Graph Varnishing and Preservation

• Permanent Fixation
  • Cut smoked paper with graphs
  • Immerse in 2% celloidin resin or methylene spirit for permanent fixation
  • Dry and preserve fixed graphs for study

Summary

• Understand apparatus setup and muscle preparation
• Differentiate between preloaded and afterloaded preparations
• Analyze simple muscle twitch and fatigue curves
• Observe effects of temperature and multiple stimuli on muscle contraction
• Study graph preservation techniques for documentation

Final Note

• For further reading, refer to additional curves and detailed explanations in the textbook.