bme403_muslec5_2006

bme403_muslec5_2006 - Muscle Sliding Filament Theory The...

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Muscle Sliding Filament Theory The interaction of actin and myosin and ATP hydrolysis underlies muscle contraction. ATP ADP + Pi + energy In the absence of ATP muscles are rigid with actin and myosin attached. This is called rigor mortis. Using the analogy of a canoe paddle(myosin head) and water(actin) this is when the paddle is dragging in the water after the power stroke. Note that the paddle is cocked in the downward position analogous to the near 45 degree angle of the myosin head during rigor mortis. With the expenditure of energy a canoe paddle can be lifted out of the water. This step relates to binding and partial hydrolysis of ATP which when complete repositions the myosin head to 90 degrees with respect to actin but not binding to actin. This is now the relaxed state which is analogous to a paddle positioned above the water in the forward position(like waiting to start paddling at the start of a race). The initiation of a contraction requires the liberation of calcium ion on the inside of the muscle cell. This step will be discussed later under excitation-contraction coupling. The power stroke consists of dipping the paddle into the water and a backwards pull which corresponds to actin-myosin attachment and return to the 45 degree conformation. ADP and Pi are also liberated. This brings us back to the rigor mortis state. This cycle will continue as long as ATP is present and calcium ion continues to be present . Excitation-Contraction Coupling The neuromuscular junction is where the motor nerve transmits the nerve impulse to the muscle. Each muscle fiber has one neuromuscular junction. When an action potential
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bme403_muslec5_2006 - Muscle Sliding Filament Theory The...

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