Physiology - Force Generation by the Heart Flashcards
Cardiac muscles have neuromuscular junctions. True or false?
False, they don’t. Instead they have gap junctions which couple the cardiac myocytes together. Slide 5
What are desmosomes role in cardiac muscle?
Provide mechanical adhesion between each cardiac cell. Make sure the tension developed by one cell will pass on to the next. Slide 6
What is a muscle cell composed of?
Many myofibrils.
They have alternating segments of thick and thin filaments called actin and myosin. Slide 7
Muscle contraction depends on what 2 external molecules and what role do they play?
ATP - phosphorylates myosin head
Ca - binds to troponin causes tropomyosin to unveil the active site on actin for myosin to bind. Slide 12
How does the action potential stimulate the contraction of muscle cells?
During the plateau phase there is an influx of Ca. Ca triggers the release of more Ca from the sarcoplasmic reticulum. This allows the Ca to bind to troponin and contraction can occur. Slide 18
What is significant between the long refractor period from the muscle action potential to the end of the contraction?
No other action potentials cause trigger more contractions otherwise there would be tetanic contraction. Slide 22
What are the two ways stroke volume can be regulated?
Extrinsic and intrinsic mechanisms. Slide 24
What is the intrinsic control of stroke volume and how does it work?
Changes in the length of muscle fibres when it is relaxed cause cause different stroke volumes.
The end diastolic volume can determine the cardiac preload. Slide 25
What is the Frank-Starling Mechanism?
The more the ventricle is filled during diastole, the larger the volume ejected during systole. Slide 26
What can effect end diastolic volume?
Increased venous return. Slide 26
What impact does an increased afterload have?
The heart is at first unable to eject the full SV so it increases the EDV.
This means the force of contraction increases and if it continues for a while it can cause hypertrophy of the muscle to overcome resistance. Slide 31
What is the extrinsic control of stroke volume?
Nerves and hormones. Slide 32
Which part of the heart is innervated by the sympathetic nerve fibres and what impact does it have on that muscle?
The ventricular muscle.
The sympathetic fibres cause an increase in the force of contraction which is a positive inotropic effect. Slide 32
What are the hormones which are the extrinsic control of stroke volume?
Adrenaline and noradrenaline from the adrenal glands. Slide 38
