Control of heart function

Question 1

What are the 3 phases of nodal cell action potential?

Answer 1

Prepotential (phase 4), upstroke (phase 0) and repolarisation (phase 3). Continually repeats.

Question 2

In a nodal cell action potential what causes the upstroke phase?

Answer 2

Calcium influx.

Question 3

In a nodal cell action potential what causes the repolarisation phase?

Answer 3

Potassium efflux.

Question 4

In a nodal cell action potential what causes the prepotential phase?

Answer 4

Sodium influx through funny channel.

Question 5

What results in different parts of the heart having different action potential shapes? e.g why does the bundle of his have a different action potential shape to the SAN

Answer 5

Different ion currents flowing and different ion channel expression in cell membrane.

Question 6

5 phases of cardiac muscle action potential?

Answer 6

Upstroke (Phase 0), Early repolarisation (Phase 1), Plateau (phase 2), repolarisation (phase 3), Resting membrane potential (phase 4).

Question 7

Why is there a plateau phase in cardiac muscle action potential?

Answer 7

Maintains cell at level of depolarisation. Long, slow contraction is required to produce effective pump.

Question 8

What is the absolute refractory period?

Answer 8

Time during which no AP can be initiated regardless of stimulus strength.

Question 9

What is the relative refractory period?

Answer 9

Time during which an AP can be initiated if larger stimulus is provided.

Question 10

Depolarisation/upstroke in cardiac muscle action potential is caused by what?

Answer 10

Sodium influx.

Question 11

Early repolarisation in cardiac muscle action potential is caused by what?

Answer 11

Potassium efflux.

Question 12

Plateau in cardiac muscle action potential is caused by what?

Answer 12

Calcium influx.

Question 13

Repolarisation in cardiac muscle action potential is caused by what?

Answer 13

Potassium efflux.

Question 14

How does parasympathetic nervous system decrease heart rate in relation to the action potential fired from SAN?

Answer 14

Makes prepotential slower. Overall action potential is slower.

Question 15

How does sympathetic nervous system increase heart rate in relation to the action potential initiated by SAN?

Answer 15

Makes prepotential (phase 4) faster. Overall action potential is faster.

Question 16

What is positive chronotropy?

Answer 16

Increase in heart rate.

Question 17

What is positive inotropy?

Answer 17

Increase in contractility.

Question 18

What is your main parasympathetic nerve?

Answer 18

Vagus nerve.

Question 19

What receptor is at preganglionic synapse?

Answer 19

Nicotinic acetylcholine receptor.

Question 20

Where is vasomotor centre located?

Answer 20

Medulla and lower third of pons.

Question 21

What is the pressor area in vasomotor centre responsible for?

Answer 21

Vasoconstriction.

Question 22

What is the depressor area in vasomotor centre responsible for?

Answer 22

Vasodilation.

Question 23

Lateral portions of vasomotor centre regulate what?

Answer 23

Heart rate and contractility.

Question 24

Medial portion of vasomotor centre does what?

Answer 24

Decreases heart rate via vagus nerve.

Question 25

What receptor on the heart do parasympathetic nerves act on?

Answer 25

M2 receptor.

Question 26

How does acting on M2 receptor inhibit contractility?

Answer 26

Activates Gi protein which inactivates adenylate cyclase.

Question 27

What receptor on the heart do sympathetic nerves act on?

Answer 27

Beta 1 receptor.

Question 28

What in the kidney is innervated by sympathetic nervous system?

Answer 28

Afferent and efferent arterioles but afferent is the primary site of sympathetic activity.

Question 29

How does sympathetic nervous system act on the kidneys to increase blood volume?

Answer 29

Acts on alpha one adrenoreceptor to cause vasoconstriction of afferent arteriole that enters glomerular capsule. Decrease in glomerular filtration which results in decreased sodium excretion. Increase in blood volume.

Question 30

What receptor do sympathetic nerves act on to secrete renin?

Answer 30

Beta 1 adrenoreceptor.

Question 31

Where are volume sensors in cardiovascular system?

Answer 31

Large pulmonary vessels, right atria.

Question 32

What occurs when less blood is arriving in the right atria?

Answer 32

Decrease in filling, decrease in baroreceptor firing and so increase in SNS activity.

Question 33

What occurs when lots of blood is arriving in the right atria?

Answer 33

Increase in distention, increase in baroreceptor firing and so decrease in SNS activity.

Question 34

What nerves do volume and pressure sensors send signals through?

Answer 34

Glossopharyngeal and vagus nerves.

Question 35

Where are pressure sensors in the cardiovascular system?

Answer 35

Aortic arch, carotid sinus and afferent arterioles in the kidney.

Question 36

How do pressure sensors regulate heart rate?

Answer 36

Increase in pressure, increase in baroreceptor firing, decrease in SNS activity. Vice versa.

Question 37

What does constriction of veins do to venous return?

Answer 37

Reduces compliance and increases venous return.

Question 38

What is central venous pressure?

Answer 38

Mean pressure in right atrium.

Question 39

What increases venous pressure and hence increases venous return?

Answer 39

Increase in blood volume, skeletal muscle pump, respiratory movements and SNS activation of veins.

Question 40

Local vasodilators?

Answer 40

Nitric oxide and prostacyclin.

Question 41

Local vasoconstrictors?

Answer 41

Thromboxane A2 and endothelins.

Question 42

Systemic vasodilators

Answer 42

Kinins (stimulate NO synthesis) and atrial natriuretic peptide (ANP).

Question 43

What receptor does vasopressin bind to cause vasoconstriction?

Answer 43

V1 receptor.

Question 44

What hormones does angiotensin II increase release of?

Answer 44

AVP and aldosterone.

Question 45

When is atrial natriuretic peptide released?

Answer 45

Secreted from the atria in response to stretch to lower blood pressure.