L12 - Myocardial Mechanics Flashcards Preview

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Flashcards in L12 - Myocardial Mechanics Deck (39)
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What describes the electrical excitation leading to contraction

Excitation - contraction - coupling


What does excitation contraction coupling describe

The electrical excitation leading to the contraction


What is the role of the T-tubules

Cause activation of many sarcomeres at one time
Leads to a faster contraction


What is the structure of the T-tubules - how does this relate to their function

Invaginations of the sarcolemma
They allow the depolarisation to spread deep into the cell


What do intercalated discs contain

Ion channels


What is the role of the intercalated discs
What does this form?

Between the ion channels - this ionically links the myofibrils forming a functional syncitium


Describe the sarcoplasmic reticulum

Fluid filled membranous sac - acts a as Ca store


Where are the cisterns found

At the end of the SR


What do T-tubules and cisterns form



Describe the sliding filament theory / state for a relaxed muscle

Ca in sarcoplasm low
Ca pumps sequester Ca in SR
Tropomyosin obscures the actin-myosin binding site preventing cross bridge formation


What is the role of calsequesterin

Binds to free Ca in the SR - gives impression that Ca is SR is low so pumps can work faster


Describe sliding filament theory when muscle is contraction

Propagation of AP along T-tub activation of VGCC
CA SR rises
Ca binds to Tn-C
Conf change in tropomysosin - actin mysoing binding site exposed
Cross bridge can form and cycling can occur if ATp/ADP/Pi available


What is muscle tension proportional to

The number of cross bridges


What is the number of cross bridges proportional to

The length of the sarcomere


What produces a maximum tension generation

An optimum resting length


Why isnt max tension gen. with short sarcomeres

Because of overlapping thin filaments


What isnt max tension gen. with long sarcomeres

Reduced area for cross bridge formation so less tension is generated


What differs between the heart and other muscles - what are the implications of this

Heart is not bound by any joints so it is possible for it to go beyond the optimum length
This leads to less force ==> so more blood left in with each contraction and can lead to heart failure


What is the optimum sarcomere length for cardiomyocytes

2.2 - 2.6 um


Describe the process that would be undertaken to measure length-tension

Clamped muscle held fixed at one end - other end attached to a force transducer
Electrical stimulation via electrode
Record l of muscle and force gen by the contraction
Lengthen muscle and repeat over a range of muscle lengths


What happens to the active force as sarcomere length increases

Starts increasing to a maximum and then decrease


What happens to passive force as sarcomere length increases

At 0 until high sarcomere length then increases


What happens to total force as sarcomere length increases

Increases - peaks - begins to decrease as active force decreases BUT passive force increases so total froce begins to increase


Describe how an engineer would model a cardiomyocyte

One contractile element with a critcal damper to prevent oscilations
One spring in parallel - representing the neck of the cross bridge
One spring in series - representing the accessory protein of the sarcomere (titin)


What length sarcomere is produced by a 10-12 mmHg filling pressure

2.2. um
this is the presystolic volume


What is a key difference in the regulation of tension between cardiac and skeletal myocyte

In cardiac greater regulation at the cellular level
In skeletal muscle to cause greater tension more fibres are recruited
In caridac the force produced by each myocyte is changed


What is isotonic contraction

Where tension does not change but the length does change


What is isometric contraction

Length is unchanged but the tension does change


Describe the relationship of the muscle, pre load and the afteload

Muscle is streched by the preload which stimulates it to lift the afterload


What is the preload

Initial streching of the sarcomere length
The ventricular end diastolic volume