ANAT 025 Lecture Notes - Lecture 6: Endoplasmic Reticulum, Myosin Head, Sarcolemma
25 May 2020
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Document Summary
Resting sarcolemma is polarized, meaning a voltage exists across membrane. Inside of cell is negative compared to outside. Action potential is caused by changes in electrical charges. Ach released from motor neuron binds to ach receptors on sarcolemma. Causes chemically gated ion channels (ligands) on sarcolemma to open. K+ efflux out of cell rapidly brings cell back to initial resting membrane voltage. Ionic conditions of resting state are restored by na+-k+ Excitation-contraction (e-c) coupling: events that transmit ap along sarcolemma (excitation) are coupled to sliding of myofilaments (contraction) Ap is propagated along sarcolemma and down into t-tubules, where voltage- sensitive proteins in tubules stimulate ca2+ release from sr (sarcoplasmic. Ap is brief and ends before contraction is seen. Voltage-sensitive proteins in t tubules change shape, causing sr to release ca2+ to cytosol. At higher intracellular ca2+ concentrations, ca2+ binds to troponin. Troponin changes shape and moves tropomyosin away from myosin-binding sites.
