Question

7. Electrical and contractile events of muscle are related, and their timing is sequential. Explain these pictures - what happens during the lag? Twitch Omv- action potential Skeletal -90 mV contraction cardiac - relaxation phase contraction phase delay Action potential teau phase Muscle contraction Muscle contraction MV or muscle contraction MV or musde contraction 100 300 100 200 200 Time (ma) Time (ma)

Answer 1

Excitation (action potential) and Contraction of muscle

According to Huxley and Taylor (1958), the excitation and contraction of muscle based on composite optical and electro-physiological experiment and the movement of calcium ions. The muscle contraction is very quickly stimulated during nerve supplying. When the action potential spread over the muscle fibre membrane, the action potential is also transmitted to the interior of the muscle fibre through the T-tubule system and this stimulus causes muscle contraction. The action potential spread first along the cell fibre membrane, sarcolemma and T-tubule system. The cisternal vesicle contain calcium ions. When the action potential reach the sarcolemma throughout the T-tubule system and the vesicles liberate Ca⁺⁺ ions in around the sarcoplasmic fluid. The Ca⁺⁺ ions diffuse in near about myofibrils where they strongly bind with troponin and it is start the muscle contraction. Once the Ca⁺⁺ ions released from cisternal vesicles and diffused to the myofibrils, the contraction of muscle continue as long as the Ca⁺⁺ ions are still present in high concentration. However a continually active calcium pump situated in the wall of the longitudinal tubules of the sarcoplasmic reticulum pump, the Ca⁺⁺ ions back into the longitudinal tubule. Therefore muscle contraction occurs after action potential but the removaal of Ca⁺⁺ ions through the saarcoplasmic pump almost soon then it cases relaxation of the muscle again. The muscle contraction may be expressed in the following manners.