Cardiac output - Electrical events and heart rate Flashcards
What drives heart rate?
Waves of electrical activity that induces the cardiac muscles to contract.
What are the two pacemaker cells of the heart?
The atrioventricular node and the sinoatrial node.
What does the atrioventricular node do?
It connects the atria and ventricles and delays the signal to allow the atria to contract before the ventricle.
What are bundles of his?
Fast conducting myocytes that connect to the Purkinje fibres.
What are the properties of Purkinje fibres?
They are very wide to allow rapid conduction throughout the ventricle and simultaneous contraction.
What causes the pacemaker cells of the SA node to trigger an action potential?
A low resting membrane potential and Na+ leakage, leading to depolarisation.
What is the mechanism behind the action potentials in the pacemaker cells?
Sodium ions leak through the F-type channels and calcium ions move through the T-type (transient) channels to cause a threshold graded depolarisation. The opening of voltage-gated calcium L-type channels is responsible for the rapid depolarisation phase. The reopening of potassium channels and closing of calcium channels are responsible for the repolarisation phase.
What is the mechanisms behind the contraction of ventricular cardiomyocytes?
The rapid opening of voltage-gated sodium channels is responsible for the depolarisation phase. The prolonged plateau of depolarisation is due to the slow but prolonged opening of voltage-gated calcium channels and closure of potassium channels. The opening of potassium channels results in the repolarisation phase.
How does calcium produce the contraction of the cardiac muscles?
The entry of extracellular calcium ions causes the release of calcium from the sarcoplasmic reticulum. There is excitation-contraction coupling.
What is the purpose of cardiac muscles refractory period?
It allows the ventricles to fill with blood prior to pumping.
What is the definition of the refractory period?
It is the time required before it is possible to re-stimulate muscle contraction.
What does the sympathetic system innervate?
The whole heart.
What does the parasympathetic system innervate?
The SA and AV nodes.
What does the vagus nerve do and what system is it part of?
Reduce the heart beat - part of the parasympathetic system.
What does the sympathetic ganglia do and what system are they apart of?
They increase the heartbeat and regulate the force/stroke volume - part of the sympathetic system.
