Force of Contraction

Question 1

can nerve activation modify activity of striated cardiac muscles

Answer 1

No

only ANS has effect on activity

Question 2

what does cell-to-cell conduction mean

Answer 2

occurs due to gap junctions low resistance electrical communication between neighbouring myocytes

Question 3

what 2 types of junction occur between intercalated discs

Answer 3

desmosomes

gap junctions

Question 4

what is the purpose of desmosomes between intercalated discs of myocytes

Answer 4

provide tension

Question 5

by what means do myocytes contract after excitation

Answer 5

All or none

Question 6

what are muscle fibres (cells) made up of

Answer 6

myofibrils (contractile units)

Question 7

what myofibrils made up of

Answer 7

actin: thin filaments, light
myosin: thick filaments, dark

Question 8

what forms the scaromere of muscle fibres

Answer 8

actin + myosin

Question 9

how is muscle tension produced

Answer 9

by sliding actin filaments on myosin filaments

Question 10

what is muscle tension dependant on

Answer 10

Calcium

ATP

Question 11

what proteins are present on actin filament

Answer 11

tropomyosin

troponin

Question 12

what is the troponin-tropomyosin complex’s role

Answer 12

binding site of myosin forming cross bridges

Question 13

what binds to troponin

Answer 13

calcium

Question 14

what doe action potentials that excite cardiac muscle depend on

Answer 14

entry of Ca into cell triggers the release of Ca from the sarcoplasmic rectiulum (calcium induced calcium release)

Question 15

where is Calcium stored in myocytes

Answer 15

sarcoplasmic reticulum

Question 16

when does Ca enter the sarcoplasmic reticulum

Answer 16

in plateau

Question 17

why is there a long refractory period

Answer 17

prevents generation of tetanic contraction

Question 18

what is the refractory period

Answer 18

period following an AP where it is not possible to produce an AP

Question 19

what happens during the plateau phase of the ventricles

Answer 19

Na channels are depolarised closed state so can’t open

Question 20

what happens during the descending phase of myocytes

Answer 20

K channels open

K efflux

Question 21

how can SV be calculated

Answer 21

end diastolic volume (EDV) - End systolic volume (ESV)

Question 22

how is the heart regulated intrinsically

Answer 22

due to diastolic lenght and stretch of myocardial fibres

more stretch = bigger SV

Question 23

what is diastolic length/stretch determined by

Answer 23

the volume of blood in each ventricle at the end of diastole

Question 24

what does the EDV determine

Answer 24

cardiac preload

Question 25

what is EDV determined by

Answer 25

venous return

Question 26

what does Frank Starlings Curve show

Answer 26

Relationship between venous return, END DIASTOLIC VOLUME and STROKE VOLUME

Question 27

the more the ventricle is fulled with blood during diastole (EDV) the greater/less the volume of ejected blood will be during the resulting systolic contraction (SV)

Answer 27

greater

Question 28

if venous return of the right ventricle increases what else is increased and what does this lead to

Answer 28

EDV of the right ventricle | therefore increased SV to the pulmonary artery

Question 29

if venous return of the left ventricle increases what else is increased and what does this lead to

Answer 29

EDV of the left ventricle therefore increased SV into aorta

Question 30

what is afterload

Answer 30

resistance into which the heart is pumping

Question 31

what happens if after load increases

Answer 31

at first the heart is unable to eject full SV so EDV increases force of contraction increases by Frank Starling mechanism

Question 32

how does the heart compensate for a prolonged continued increased after load eg. untreated hypertenion

Answer 32

ventricular increased muscle mass (ventricular hypertrophy) overcomes resistance

Question 33

other than increasing SV what other effect does stretch have

Answer 33

increases affinity of troponin for Ca

Question 34

what 2 extrinsic mechanisms effect the heart

Answer 34

neves - ANS | hormones

Question 35

what nerves affect the ventricles

Answer 35

Sympathetic | noradrenaline increases HR acts on B1

Question 36

what 2 effects does the sympathetic NS have on the heart

Answer 36

Positive chronotropic effect | Positive Inotropic effect

Question 37

as well as increasing rate of contraction what other effect does the sympathetic NS have on heart contraction

Answer 37

increases force

Question 38

why does the force of contraction increase by action of the sympathetic NS

Answer 38

due to activation of Ca channels | peak ventricular pressure rises: rate of pressure change during systole increases (reducing duration of systole)

Question 39

what mediates the activation of Ca channels

Answer 39

cAMP

Question 40

how does the rate of ventricular relaxation increase

Answer 40

by the increasing rate of Ca pumping reducing the duration of systole

Question 41

what direction does a positive inotropic effect have on Frank Starlings Law and why

Answer 41

shift to the left | increased SV therefore peak ventricular pressure rises, contractility of the heart at a given EDV rises

Question 42

what direction does a negative inotropic effect eg in heart failure have on Frank Starlings Law

Answer 42

shift to right

Question 43

what 2 hormones effect the heart by having chronotropic and inotropic effects

Answer 43

adrenaline and noradrenaline (minor compared with sympathetic NS)

Question 44

define cardiac output

Answer 44

volume fo blood pumped by each ventricle per minute

Question 45

equation to calculate CO

Answer 45

CO = SV x HR