Lecture 14 – Muscle Physiology II

During t tuble ap conformationcal change of dhp

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During T-tuble AP, conformationcal change of DHP receptor act via the foot processes  to open rYR Ca channel Ca is released from the later sacs of the SR into the cytosol activating cross-bridge  cycling Rise in cytosolic Ca arising from a single action potential is enough hto saturate all the  troponin binding sites on the thin filaments
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End of Contraction Terminated by the removal of Ca from troponin which is cuased by lowering the cytosolic  Ca back to its prelease level This occurs because the membranes of SR contain Ca-ATPases Active transport proteins ADDITIONAL role of ATP in muscle contraction This takes time – elevated Ca levels for a long time after the initial AP
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Summary of Neuron AP and Muscle Contraction
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Changes in banding pattern during sarcomere shortening H-zone shortens Becomes just the length of the dead zone I band shortens Because there is more actin-myosin overlap
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A band is same width Timing of Cellular Events  Threshold releases Ca Threshold is quick, normal AP  CA spikes and then slowly decreases WHILE TROP is still becoming inactive TROP complex decreases in a gradient Force of contraction increases as TROP action decreases
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Timing of Ca and Force Production
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Mechanics of Single Fiber Contraction Types of Contraction Tension – the force extered on an object by a contracting muscle Load – the force exterted on the muscle by and object (usually the weight of an object) Muscle tension and load are opposing forces Whtereh a muscle fiber shortends depends on the relative magnitude of load and  tension For a muscle fibr to shortn and move a load, muscle tension must be greater than the  opposing load When a muscle develops tension but does not shorten (or lengthen) the  contraction is isometric Such contraction occurs when the muscle suppors a load in a constant position or  attempts to move a load when the load is greater than the tension developed by the  muscle
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A contraction in which the sarcomere changes length while the load remains  constant is isotonic Isotonic Contraction Depending on the relative magnitudes of tension and opposing load, isotonic contraction  can either result in shortenind or lengthening of the muscle If tension is greater than load, shorteing occurs and its is called concentric contraction If load is greater than tension, lengthening occurs and it is called eccentric contraction
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