force generation by the heart

Question 1

what is the composition of cardiac muscle

Answer 1

• 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

Question 2

what is the structure of striated muscle fibres?

Answer 2

• 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

Question 3

how is muscle tension produced?q

Answer 3

by sliding of actin filaments on myocin filaments - shortens and produces force

Question 4

what does force generation depend on?

Answer 4

ATP-dependetn interacton between thick (myosin) and thin (actin) filaments

Question 5

T/F - ATP is required for both contraction and relaxation?

Answer 5

true

- to help from/ destroy cross bridge structure

Question 6

what is required to switch on cross bridge formation?

Answer 6

Ca++

binds to troponin , allowing myocin to attach to actin

Question 7

where is Ca++ released from?

Answer 7

the sarcoplasmic reticulum (SR)

-release is dependent on presence of extra-cellular Ca++ (need it to enter cell)

Question 8

during what phase of the cardiac cycle does the ventricular muscle relax?

Answer 8

diastole

Question 9

during what phase of the cardiac cycle does the ventricular muscle contract?

Answer 9

systole

Question 10

what is the refractory period?

Answer 10

a period following an action potential in which it is not possible to produce another action potential

Question 11

what does the long refractory period do?

Answer 11

• 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

Question 12

what is stroke volume?

Answer 12

the volume of blood ejected by each ventricle per heart beat

Question 13

how do you calculate SV?

Answer 13

end diastolic volume (EDV) - end systolic volume (ESV) = SV

Question 14

define intrinsic

Answer 14

within the heart muscle

Question 15

define extrinsic

Answer 15

nervous and hormonal control

Question 16

how is optimal length in cardiac muscle achieved?

Answer 16

by stretching the muscle

Question 17

how is the affinity of troponin for Ca++ increased?

Answer 17

by stretching muscle

- achieved by bringing in more blood

Question 18

define afterload

Answer 18

the resistance into which heart is pumping

Question 19

describe extrinsic control of stroke volume

Answer 19

• involves nerves and hormones
• sympathetic nerve fibres
• noradrenaline
• stimulation of sympathetic nerves increases the force of contraction = inotropic effect

Question 20

what is the effect of sympathetic stimulation on ventricular contraction

Answer 20

• peak ventricular pressure rises
• force contraction increases
• reduces the duration of systole

Question 21

what is cardiac output?

Answer 21

the volume of blood pumped by each ventricle per minute

Question 22

how do you calculate cardiac output?

Answer 22

CO= SV x HR

Question 23

what is the resting CO in a health adult?

Answer 23

approx. 5 litres per minute