Myocardial mechanics Flashcards
What kind of signalling leads to myocardial contraction
Electrical
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
- Troponin I moves away from the actin/tropomyosin filament, allowing tropomyosin molecule to move away from the myosin binding site
- 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.
