VPB 121: Veterinary Physiology - II (2+1)

SIMPLE MUSCLE CURVE - PROCEDURE

• Muscle-nerve preparation as previous exercise and arrange the electrical apparatus for faradic current to induce electrical stimulation.
• Adjust the distance between the primary and secondary coils to get single maximal break induced stimuli.
• Fix the simple electrode on the moist fiber paper on the frog board. Gently place the nerve on the electrodes without tension .
• Keep the cross block in the myograph stand to hold the muscle grip exactly horizontal to the main axis of the myograph stand and fix the femur .
• Tie the thread from the tendon to the isotonic lever with a distance of 1.5 - 2” and 90° angle.
• Keep the afterload screw in released position and fix the dead weight after the knot of the thread towards the afterload screw.
• Keep the writing point of the lever at appropriate distance from the fulcrum and ensure the free movement of the pointer with optimum pressure over the recording drum about 3” height for every contraction of the muscle.
• Once this adjustment is made the base of the myographic stand should not be disturbed.
• The pointer should be applied to the drum or removed away from the drum only by means of the knob at the base of the myograph stand.
• Switch on the recording drum. When the contact arm touches the contact knob the muscle is stimulated to contract and the pointer of the isotonic lever moves up on the recording drum to draw a curve.
• Switch off the Kymograph and rotate the drum by hand till the contact arm touches the contact knob.
• At this position , circuit was completed and nerve was stimulated.
• Mark a line on the base line by raising the lever about 1 centimeter with finger and label it as A. This point represents the point of stimulus.
• Similarly make arcs
  • at the point where curve leaves the base line, label it as B.
  • at the highest point of curve (C) and
  • at the point where curve retouches the base line (D)
• Move the lever point away from the drum. Set the drum rotating with the same speed as before and record vibrations of a tuning fork of known frequency (100 vibrations per second) below the base line.
• The distance between two peaks will be 1/100 th of a sec. Measure the time interval (seconds) for Latent (AB), Contraction (BC) and Relaxation periods (CD).
• Latent period is the time interval between application of stimulus and onset of contraction.It is due to
  • Time required for conducting nerve impulse along nerve fibre to the motor end plate.
  • Time taken for the release of neuro transmitter i.e. Acetyl Choline from nerve terminal and its diffusion in the neuro muscular junction
  • Time taken for chemical changes to occur in the muscle (true latent period) and
  • The time taken for overcoming the inertia of the lever.
• Latent period – 0.01 second, Contraction period – 0.04 second, Relaxation period – 0.05 second.
• Relaxation is a passive process while contraction is an active process. Hence the relaxation period is longer than contraction period.