force generation by the heart Flashcards
what is the composition of cardiac muscle
- striated -> caused by regular arrangement of contractile protein
- cardiac monocytes are electrically coupled by gap junctions
- protein channels that form low resistance electrical communication pathways between myocytes
- these communication pathways ensure all cardiac myocytes recieve the electrical excitation
- desmosomes provide mechanical adhesion between cardiac cells
- one muscle fibre is one muscle cell
what is the structure of striated muscle fibres?
- contains many myofibrils (contractile units)
- actin (thin filaments) cause the lighter appearance
- myocin (thick filaments) cause darker appaerance
- within each myobibril actin and myocin are aranged into sacromeres
how is muscle tension produced?q
by sliding of actin filaments on myocin filaments - shortens and produces force
what does force generation depend on?
ATP-dependetn interacton between thick (myosin) and thin (actin) filaments
T/F - ATP is required for both contraction and relaxation?
true
- to help from/ destroy cross bridge structure
what is required to switch on cross bridge formation?
Ca++
binds to troponin , allowing myocin to attach to actin
where is Ca++ released from?
the sarcoplasmic reticulum (SR)
-release is dependent on presence of extra-cellular Ca++ (need it to enter cell)
during what phase of the cardiac cycle does the ventricular muscle relax?
diastole
during what phase of the cardiac cycle does the ventricular muscle contract?
systole
what is the refractory period?
a period following an action potential in which it is not possible to produce another action potential
what does the long refractory period do?
- protects heart
- prevents generation of tetanic (sustained contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.) contractions in the cardiac muscle
what is stroke volume?
the volume of blood ejected by each ventricle per heart beat
how do you calculate SV?
end diastolic volume (EDV) - end systolic volume (ESV) = SV
define intrinsic
within the heart muscle
define extrinsic
nervous and hormonal control
how is optimal length in cardiac muscle achieved?
by stretching the muscle
how is the affinity of troponin for Ca++ increased?
by stretching muscle
- achieved by bringing in more blood
define afterload
the resistance into which heart is pumping
describe extrinsic control of stroke volume
- involves nerves and hormones
- sympathetic nerve fibres
- noradrenaline
- stimulation of sympathetic nerves increases the force of contraction = inotropic effect
what is the effect of sympathetic stimulation on ventricular contraction
- peak ventricular pressure rises
- force contraction increases
- reduces the duration of systole
what is cardiac output?
the volume of blood pumped by each ventricle per minute
how do you calculate cardiac output?
CO= SV x HR
what is the resting CO in a health adult?
approx. 5 litres per minute
