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Lecture

3. Contraction.docx

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Department
Kinesiology
Course Code
Kinesiology 2230A/B
Professor
Glen Belfry

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Description
Lecture 3 Spinal Cord Injury • You lose all function below the injury Sacral: lose all but some innervation to lower legs Lumbar: lose some function in legs (may have some adduction of legs) Thoracic: lose function below arms Cervical: lose all function below the neck If there is a shearing action that occurs you will lose the connection below that area • Nerve fibres do heal in a minor fashion but if there is a major section of a nerve injured it will never heal. Animations: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter45/animations.html# Recall: The action potential in the post-synaptic terminal is similar to that of the nerves, except that the stimulation for depolarization is not voltage but the binding of acetylcholine to ligand-gated channels. • Assuming the stimulus ceases, the acetyl-cholinesterase splits the acetylcholine to create choline and acetic acid • Choline is reabsorbed back into the pre-synaptic terminal. Acetic acid is lost. The action potential moves down the cell (sarcolemma) membrane. AP then passes through T tubules which are perpendicular to the myofibrils. This stimulates the release of calcium from the sarcoplasmic reticulum (where it is stored). • This bathes the contractile proteins which gives a contraction of the filaments. (fence like structure) The Sarcoplasmic Reticulum functions to uptake calcium from the sarcoplasm and to release calcium into the sarcoplasm to initiate contraction and sequester it during relaxation Triad On both sides of a T-tubule are dilated end sacs of the sarcoplasmic reticulum called the terminal cisternae. A T-tubule, together with its two terminal cisternae, is called a muscle triad • Terminal cisternae is where the calcium is stored. As long as there is calcium available, the interaction of myosin and actin will continue to occur. • When the action potential ceases, calcium is moved back into SR. This is an energy consuming process - Ca+ ATPase pump Muscle Contraction ATP use: Na/K ATPase pump during nerve conduction, contraction of muscle (myosin head), Ca+ ATPase pump after relaxation Mechanism of Muscular Contraction Sliding Filament Hypothesis: a cycle of repetitive events that cause a thin filament to slide over a thick filament and generate tension in the muscle H zone (at rest) is the distance between the two actin filaments • As the muscle contracts, the myosin doesn’t change position but the H zone shortens I band is the distance of one end of the myosin and the other myosin on the other side of the z line • Also gets smaller during contraction A band is the length of myosin itself • Doesn’t change Mechanism of Actin and Myosin Interaction Slide 61 shows animation of myosin and actin interaction Tropomyosin ropes around actin covers the active sites on actin to which myosin binds in order to generate force • Troponin moves tropomyosin that has been covering the binding sites of the myosin head when it combines with released calcium  It has a high affinity to calcium (calcium release bathing myofibrils)  Tropomyosin shifts once troponin interacts w/ calcium Magnesium activates ATP hydrolysis. This initiates the splitting of the ATP molecule in the presence of Myosin ATPase  Energy is released  Myosin head swivels  Muscle begins to shorten Myosin head is still attached to tropomyosin when it splits When ATP binds to myosin head, that is what signals release of myosin head from tropomyosin • Very little energy required, do not need to split an ATP Link between actin, myosin and ATP • Energy is provided fo
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