Myocardial Mechanics

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Myocardial Mechanics

Electrical contraction - muscle contraction --> T tubules and intercalated discs rapidly transmit action potentials in the myocardium. Calcium levels rise during the plateau phase. Calcium entry into the cell and release from intracellular stores (SR) bind and displace the troponin/tropomyosin complex from actin.

Myosin contracts actin, and filament sliding commences --> contraction.

Consequence of sliding filaments

Muscle tension should be proportionate to crossbridges/number of interactions between myosin and actin. The number of crossbridges should be proportional to sarcomere length.

Short sarcomeres have overlapping thin filaments --> tension should be proportionate to muscle length.

Muscle length before contraction should be related to how much tension there will be. Sarcomere length before stimulation against tension generated upon stimulation goes up to a point (where overly contracted) then around peak it is optimum resting length, then from ther goes down as over-stretched.

Length-tension relationship

For part of it there is a linear relationship between length and tension. Used papillary muscle to test the prediction (as it's difficult to dissect out the ventricle wall, so outer ventricle muscle is used). used electrodes. Measurmentwas under isometric conditions. Stimulated muscle to contract but it didn't actually change length (isometric). Isotonic = no change in tension

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