Lect18 - Jan31 - Muscle IV and Cardio I

Lect18 - Jan31 - Muscle IV and Cardio I - Frequency...

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Muscle 1, 2 & 3 Frequency and Spatial Summation 1/22/11 26 AKA Unfused Tetany Fig. 8-18, p. 271 Fig. 8-17, p. 270 Frequency summation = temporal summation. since the duration of a nerve AP is less than the duration of a muscle AP which is also less than the duration of a muscle contration, summation may occur. Successive activation --> increases the contractile for due to the increase in stready state Ca2+ concentration. In skeletal muscle, this increases the duration of crossbridge cycling --> increased sarcomere shortening. stimulate again before it relaxes - unfused tetany - increase the amount of tension stimulate at high frequency. activate the skeletal muscle again before it begins to relax (decrease Ca2+ concentration). At very high frequency --> fusion = tetany Also able to grade force of contraction by recruiting more motor units. Motor units also have di f erent sizes. The increment of tension development is de±nied by the size of the motor units being recruited. small motor units large motor units
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Smooth Muscle Contractile Proteins & Excitation – Contraction Coupling Myosin & Actin + Tropomyosin. No troponin . There are three other regulatory proteins, Calmodulin , Caldesmon & Calponin (not shown). Myosin and Actin not organized into sarcomeres long strands of actin linked in lattice structure. Actin and their regulatory proteins are linked at Dense Bodies . Myosin staggered between dense bodies along actin and regulatory proteins. 1/22/11 27 Fig. 8-31, p. 295 Smooth muscle - has actin, myosin, and tropomyosin. No troponin. smooth muscle has no striations - di f erent physical relationship between A and M. Actin formas a lattice network, connected together at Dense Bodies. M staggered along the lattice. M binding to A depends on ~p (phosphorylation) of myosin light chain (MLC). M binds to A if MLC~p. This ~p is mediated by Ca2+ binding to Calmodulin. Ca2+ is still required for muscle contration in smooth muscle. additional regulatory
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Lect18 - Jan31 - Muscle IV and Cardio I - Frequency...

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