A SINGLE MUSCLE TWITCH AND TETANIC CONTRACTION Li

A SINGLE MUSCLE TWITCH AND TETANIC CONTRACTION Li Jingxin Physiologcal Department

A SINGLE MUSCLE TWITCH • When a muscle is stimulated, it contracts after a latent period and this is immediately followed by relaxation, this is called single muscle twitch. Start stimulating 1 2 3 1. latent period 2. contraction period 3. relaxation period

TETANIC CONTRACTION • When a muscle is stimulated at very high frequency(100/s), the successive contractions completely fuse together and cannot be distinguished one from the other. This state of sustained contraction is called Tetanization.

Prepare a nerve and muscle preparation Sciatic nerve-gastrocnemius of frog

Quadriceps femoris biceps femoris Semimembranous muscle biceps femoris semimembranous muscle femur

procedure 1. fix the knee joint with the help of pins 2. tie the tendon and cut it below the thread 3. cut all the structures below the knee joint except gastrocnemius muscle

• 4. connect the tendon to tension transducer with hook of clip • 5. Place the nerve over electrodes

Tension transducer Sciatic nerve-gastrocnemius muscle preparation or Powerlab Stimulus output

Set up stimulator • Open the computer double click “chart for windows” • Set up select “stimulator” : Mode “pulse” ; select “set number of pulses 10 or 15” • Select “ stimulator panel”: frequency 1; pulse duration 1 ms; Amplitude 3 v • Select “Even marker” select “channel 2” • Switch on “stimulator” , Adjust “ sampling velocity and sensitivity” and obtain a normal curve.

Observation • 1. Increase frequency 6 stimuli/second • 2. Go on increasing frequency 15 stimuli/second

IMPORTANT QUESTIONS • 1. What is a single muscle contraction or twitch? What does it consist of? • 2. what is TETANIC CONTRACTION? What is its cause?