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Flashcards in Myocardial mechanics Deck (21)
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What kind of signalling leads to myocardial contraction



What two structures lead to rapid transmission of action potentials in the myocardium

Intercalated discs and T-tubules


When does calcium concentration rise during the myocardial potential

During the plateau phase - 100nm to 1-10um


By what mechanism does calcium rise intracellularly

Calcium induced calcium release - Calcium intracellularly is able to activate calcium release from intracellular stores in the sarcoplasmic reticulum


How does calcium interact with the troponin/tropomyosin complex with actin

1. Troponin I moves away from the actin/tropomyosin filament, allowing tropomyosin molecule to move away from the myosin binding site
2. Transmission through troponin T, tropomyosin is pushed away from the myosin binding site into the actin groove - myosin head is able to interact with actin to form cross bridge linkage


What is muscle tension proportional to?

The number of crossbridges formed


What is the number of crossbridges formed proportional to and why

Sarcomere length - If the sarcomere is too short the thin filaments overlap creating less tension
If they are too long then there are reduced areas for crossbridge formation between thick and thin filaments


Define isometric contraction

Contraction where the length of the muscle is fixed but the amount of tension is changed due to contraction


Define isotonic contration

The amount of tension on the muscle is fixed but upon contraction, the length of the muscle shortens - provided that the force of contraction is greater than the preload


At what length of the sarcomere is the max tension produced and why

2.2um because the max number of crossbridge formation occurs at this length


What produces the 2.2um sarcomere length in the heart

10-12mmHg filling pressure - pre-systole


How is papillary muscle used to investigate force-velocity relationship

Tension transducer connected to papillary muscle
Papillary muscle initially stretched from pre load - represents sarcomere length after diastole
It's then stimulated to lift an afterload - Represents the force in which ventricles act against to eject blood (arterial blood pressure)


Why is Vmax a constant

Indicates the cardiac muscles contractility which stays the same - investigation into speed


What happens to speed of contraction as the afterload is increased and what is the physiological reason behind this

Slows down - Higher afterload represents higher blood pressure in the arteries so the slower the heart is able to eject blood


What happens to any given afterload if you increase the preload

There is an increased velocity - increasing preload increases max force


what causes a change in contractility

When the heart changes the output per beat when the end diastolic volume is constant


How does contractility increase

Due to increased calcium concentrations intracellularly causing more crossbridge formations per stimulus


What is a chronotropic effect

A change in rate


What is an inotropic effect

A change in contractility


What effect does noradrenaline have on contraction

Positive inotropic and chronotropic effects (increased max force and max velocity of contraction)


How does frequency of contraction also influence the force of contraction

An increase in frequency causes an increase in contractility - because the intracellular calcium builds up due to there not being enough time between beats for it to be removed to its pre original concentration.