Advanced Physiology Weekly Questions - Week 10 (H1) PDF

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Summary

Describe/define the source of both active and passive force during the musclecontraction----Thin actin and thick myosinLTR = isometric force only – force developed by muscle and load are equivalent- Active force – this is whats happening at degree of overlap at each casemuscle is set in terms of len...

Description

Desc r i be/ defi net hes our c eofbot hac t i v eandpas s i v ef or cedur i ngt hemus c l e c ont r act i on

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Thi nac t i nandt hi c kmy os i n L TR=i s omet r i cf or c eonl y–f or c edevel opedbymusc l eandl oadar eequi v al ent

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When we stretch muscle but don’t stimulate it The more u stretch muscle = more muscle pull on force transducer More we stretch muscle = higher force produced in passive way (higher passive force) Long lengths see increases in passive force More we stretch = suboptimal overlap of thick and thin filaments = passive increase but active force decrease - Need sarcomere to be optimal so some degree of stretch important but overstretch muscle it compromises the overlap of filaments so active force starts to decrease - Passive increases = active decreases

- Total force = sum of passive and active force at any one time - Increase of force at optimal overlap but continue stretch = total force decrease because active component contributes less and less to overall force production - Muscle extreme stretch = total force really just by passive forces but rmb no overlap of filaments o Passive increase = active decrease = total force responds accordingly based on sum of those 2 forces - Max force generation = sarcomere needs to be at optimum lengths = optimal overlap of thick and thin filaments to produce active force The length-tension relationship (LTR) is the interaction between thin actin and thick myosin filament which overlap to form cross-bridges during isometric contractions (equal muscle force and load). This relationship is shown in the stress (kg/cm^2) vs length (fraction of optimum) graph. Active force described the degree of overlapping myofilaments at different muscle lengths. Ascending limb of the LTR, sarcomere length is short/suboptimal. Force is therefore suboptimal. This is because at short sarcomere length, the filaments are compacted together resulting in less crossbridge formation. Following this is the plateau region where there is optimal sarcomere relationship. Here, there is maximal force produced as there is optimal interaction between the filaments. As we continue to increase length (descending limb), the sarcomere length begins to excessively stretch. This results in decrease in overlapping of the myofilaments and hence less force is produced. Passive force is the force produced when the muscle is stretched but not stimulated. The more the muscle stretches the higher the force is produced (passively). As a result of increased passive force, there is pulling on the muscle force transducer. This force is dependent on the elastic component of the muscle tendons. However, as passive force increases there will consequently be a decrease in active force due to less cross-bridge formation of myofilaments during excessive stretching (descending limb). Total force is the sum of both passive and active force at any one point in time during muscle contraction. At optimal length, interaction of myofilaments account for the great proportion of active force produced, resulting in an increase of total force as well. As excessive stretching of the muscle increases and less force is produced, there is a decrease in active force which limits overall force despite increase in passive force - decrease in total force produced....