Control of heart function Flashcards
What are the 3 phases of nodal cell action potential?
Prepotential (phase 4), upstroke (phase 0) and repolarisation (phase 3). Continually repeats.
In a nodal cell action potential what causes the upstroke phase?
Calcium influx.
In a nodal cell action potential what causes the repolarisation phase?
Potassium efflux.
In a nodal cell action potential what causes the prepotential phase?
Sodium influx through funny channel.
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
Different ion currents flowing and different ion channel expression in cell membrane.
5 phases of cardiac muscle action potential?
Upstroke (Phase 0), Early repolarisation (Phase 1), Plateau (phase 2), repolarisation (phase 3), Resting membrane potential (phase 4).
Why is there a plateau phase in cardiac muscle action potential?
Maintains cell at level of depolarisation. Long, slow contraction is required to produce effective pump.
What is the absolute refractory period?
Time during which no AP can be initiated regardless of stimulus strength.
What is the relative refractory period?
Time during which an AP can be initiated if larger stimulus is provided.
Depolarisation/upstroke in cardiac muscle action potential is caused by what?
Sodium influx.
Early repolarisation in cardiac muscle action potential is caused by what?
Potassium efflux.
Plateau in cardiac muscle action potential is caused by what?
Calcium influx.
Repolarisation in cardiac muscle action potential is caused by what?
Potassium efflux.
How does parasympathetic nervous system decrease heart rate in relation to the action potential fired from SAN?
Makes prepotential slower. Overall action potential is slower.
How does sympathetic nervous system increase heart rate in relation to the action potential initiated by SAN?
Makes prepotential (phase 4) faster. Overall action potential is faster.
What is positive chronotropy?
Increase in heart rate.
What is positive inotropy?
Increase in contractility.
What is your main parasympathetic nerve?
Vagus nerve.
What receptor is at preganglionic synapse?
Nicotinic acetylcholine receptor.
Where is vasomotor centre located?
Medulla and lower third of pons.
What is the pressor area in vasomotor centre responsible for?
Vasoconstriction.
What is the depressor area in vasomotor centre responsible for?
Vasodilation.
Lateral portions of vasomotor centre regulate what?
Heart rate and contractility.
Medial portion of vasomotor centre does what?
Decreases heart rate via vagus nerve.
What receptor on the heart do parasympathetic nerves act on?
M2 receptor.
How does acting on M2 receptor inhibit contractility?
Activates Gi protein which inactivates adenylate cyclase.
What receptor on the heart do sympathetic nerves act on?
Beta 1 receptor.
What in the kidney is innervated by sympathetic nervous system?
Afferent and efferent arterioles but afferent is the primary site of sympathetic activity.
How does sympathetic nervous system act on the kidneys to increase blood volume?
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.
What receptor do sympathetic nerves act on to secrete renin?
Beta 1 adrenoreceptor.
Where are volume sensors in cardiovascular system?
Large pulmonary vessels, right atria.
What occurs when less blood is arriving in the right atria?
Decrease in filling, decrease in baroreceptor firing and so increase in SNS activity.
What occurs when lots of blood is arriving in the right atria?
Increase in distention, increase in baroreceptor firing and so decrease in SNS activity.
What nerves do volume and pressure sensors send signals through?
Glossopharyngeal and vagus nerves.
Where are pressure sensors in the cardiovascular system?
Aortic arch, carotid sinus and afferent arterioles in the kidney.
How do pressure sensors regulate heart rate?
Increase in pressure, increase in baroreceptor firing, decrease in SNS activity. Vice versa.
What does constriction of veins do to venous return?
Reduces compliance and increases venous return.
What is central venous pressure?
Mean pressure in right atrium.
What increases venous pressure and hence increases venous return?
Increase in blood volume, skeletal muscle pump, respiratory movements and SNS activation of veins.
Local vasodilators?
Nitric oxide and prostacyclin.
Local vasoconstrictors?
Thromboxane A2 and endothelins.
Systemic vasodilators
Kinins (stimulate NO synthesis) and atrial natriuretic peptide (ANP).
What receptor does vasopressin bind to cause vasoconstriction?
V1 receptor.
What hormones does angiotensin II increase release of?
AVP and aldosterone.
When is atrial natriuretic peptide released?
Secreted from the atria in response to stretch to lower blood pressure.
