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Lecture

Muscle function

2 Pages
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Department
Physiology
Course Code
Physiology 3120
Professor
Tom Stavraky

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Human Physiology Wednesday, October 7, 2009 Sliding Filament Theory • T-tubule is continuous with extracellular fluid • Thin & thick filament lengths didn’t change • Sarcomere length shortens • Myosin (thick) pulls on the actin filaments, such that the filaments slide past each other Length-Tension Curve • Maximal length of sarcomere is 3.65 microns  Tension at this point is very low • When the filaments overlap, cross-bridges can form  Maximal tension occurs at maximal overlap  Length of sarcomere is about 2.25 – 2.00 microns • When thin filaments overlap with themselves, friction prevents tension from reaching maximum • When either filaments come in contact with the Z-lines, there is no tension Excitation-Contraction Coupling • The process by which an AP in muscle leads to release of calcium from sarcoplasmic reticulum, crossbridge activity, and contraction • T-tubule is continuation of cell membrane  Thus, APs generated on end plate can travel deep into the muscle itself  Wraps around the myofibrils  Comes in contact (or very close to it) with the lateral sacs/terminal cisternae of sarcoplasmic reticulum • Sequence of events 1. AP on muscle cell travels down the T-tubules 2. Dihydropyridine (DHP) receptor/Ca channel (voltage sensor) on T-tubule changes conformation due to the AP 3. DHP receptor opens ryanodine receptor/Ca channel on sarcoplasmic reticulum 4. Ca released from terminal cisternae of SR  S
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