BIOL273 Lecture Notes - Endoplasmic Reticulum, Troponin, Sarcomere
27 May 2013
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Coupling: steps in initiation of contraction: when the muscle cell"s motor end plate depolarizes, an action potential sweeps across the cell"s membrane, and along it"s t-tubules. Ca++ concentration inside sarcoplasmic reticulum (sr) is about 100x cytoplasm of muscle cell > ca++ rushes out to cytoplasm (happens at many sites in the cell) Diffusion over a short distance is the fastest way to get sth accomplished (action potentials, synapse: ca++ bind to troponin molecules > unmasking of binding sites > contraction begins. Built into the sarcoplasmic reticulum are active transporters for ca++ = atpase pumps move ca++ from cytoplasm back into sr > concentration of ca++ falls rapidly in cytoplasm > contraction turns off. Action potential on nerve cell and action potential on muscle cell is similar (when diffusion takes place at the synapse.
