Abstract:

BACKGROUND: In the previous verification tests, muscle contraction is induced by electric stimulation. Therefore, the detected surface electromyogram signal is mixed with applied electric current. So the relations between surface electromyogram signal, muscle contraction and upper motor centers can not be fully analyzed, especially the latter one.
OBJECTIVE: To assess the relations between surface electromyogram signal, muscle contraction and upper or lower motor centers in New Zealand rabbit gastrocnemius muscle.
METHODS: The right heel tendon of a conscious rabbit was pricked by an acupuncture needle to induce gastrocnemius muscle contraction. The right sciatic nerve was severed under the local anesthesia. The intensity and category of the gastrocnemius muscle surface electromyogram signal were measured respectively when pricking the right heel tendon, clamping the distal end of the severed sciatic nerve, pricking the right gastrocnemius muscle and inducing passive gastrocnemius muscle movement. Then the spinal cord was cut off at L3 plane under the local anesthesia. The gastrocnemius muscle contraction was induced by pricking the left heel tendon. The intensity and category of the gastrocnemius muscle surface electromygram signal were measured.
RESULTS AND CONCLUSION: Under normal condition, a high magnitude (400 μV) and wide bottom (4 seconds) voluntary wave was detected when voluntary gastrocnemius muscle contraction was induced by pricking the heel tendon. After cutting off the spinal cord, a low magnitude ( < 100 μV) and narrow bottom ( < 1 second) reflex wave was detected when reflexive gastrocnemius muscle contraction was induced by pricking the heel tendon. After severing the sciatic nerve, muscle contraction cannot be induced when pricking the heel tendon, the muscle or the sciatic nerve distal end. However, some very low magnitude ( < 10 μV) and very narrow bottom ( < 0.5 second) interference wave was detected during the procedures above. No surface electromyogram signal was detected when gastrocnemius muscle was in the passive motion. These findings suggest that rabbit gastrocnemius muscle surface electromyogram signal is generated before the muscle contraction. It is a combination of drive electrical signal transmitted to muscles, which is based on upper motor center, supplemented by lower motor center. Surface electromyogram signal cannot be generated by muscle contraction itself.