Force generation by the heart Flashcards
(39 cards)
what are striations caused by?
regular arrangements of contractile protein
what are cardiac myocytes electrically coupled with?
gap junctions
what are gap junctions?
protein channels which form low resistance electrical communication pathways between neighbouring myocytes
- they ensure that each electrical excitation reaches all the cardiac myocytes
where are desmosomes found?
within intercalated discs
what is purpose of desmosomes?
provide mechanical adhesion between adjacent cardiac cells
- They ensure that the tension developed by one cell is transmitted to the next
simply what is purpose of gap junctions & desmosomes?
gap junctions = allow spread of action potential
desmosomes = allow adhesion
what is actin?
(thin filaments) causes the lighter appearance in myofibrils & fibers
what is myocyin?
(thick filaments) cause the darker appearance
what are myofibrils?
- they are found inside cardiac muscle cells (like lots of tubes in a muscle fibre)
- contain alternating segments of thick & thin protein filaments
what are sarcomeres?
each myofibril = has several sarcomeres
sarcomere is the area between actin (between light & dark on myofibril)
what is the sliding filament theory?
explanation of how muscle shortens and produces force
= overlap of actin and myosin filaments, shortening the sarcomere
- calcium needs to bind to troponin to change conformation so exposed binding site on actin for myocyin
- myocyin heads cross-bridge and bind to actin which then makes conformational change resulting in the overlap - thin filament pulled inward during contraction
what are the 2 requirements for cross bridging in muscle contraction?
- ATP
- calcium
what is tropomyosin and troponin?
they physically cover myocyin binding site on actin
- when muscle relaxed tropomyosin and troponin cover binding site
(Ca2+ binds to change conformation and uncover)
where does calcium get released from in action potential - so it can bind to troponin and tropomyosin?
- released from sarcoplasmic reticulum
- the release of Ca2+ from SR is dependent on the presence of extra-cellular Ca2+
what happens with calcium once action potential passed?
- Ca2+ influx ceases
- Ca2+ re-sequestered in SR by Ca2+ ATPase & heart muscle relaxes
what is the importance of the long refractory period?
so muscle can’t contract before other contraction finished so not sustained contraction as sustained contraction bad for heart (tetanic contraction)
→because if you could produce another action potential then loop would just keep going and sustained contraction
= by the time it’s ready to produce another action potential - contraction already over so it’s all good to contract again
what is a refractory period?
period following action potential where it isn’t possible to produce another action potential
what is stroke volume?
the volume of blood ejected by each ventricle per heart beat
how to calculate stroke volume?
SV = End Diastolic Volume (EDV) – End Systolic Volume (ESV)
what is stroke volume regulated by?
INTRINSIC and EXTRINSIC mechanisms
what is diastolic length/stretch of myocardial fibers determined by?
the end diastolic volume = the volume of blood within each ventricle at the end of diastole
what determines the cardiac preload?
= end diastolic volume
what is the cardiac preload?
the diastolic length/diastolic stretch of myocardial fibers
= the force that stretches the cardiac muscle prior to contraction
what is relationship between end diastolic volume and venous return?
end diastolic volume is determined by the venous return to the heart (larger EDV means larger cardiac preload)
