Topic 1 CVS Lecture 2 Flashcards
What is the predicted maximum heart rate?
220-age(years)
What effect does exercise training have on resting heart rate?
Decreases resting heart rate.
How can heart rate be used to measure aerobic fitness?
The fitter you are the quicker your heart rate will return to resting rate.
Why do cardiac muscle cells have a long absolute refractory period?
To help maintain coordination between the cells to keep order in contraction to make an effective heartbeat.
How is electrical conduction passed along cardiac myocytes?
They are connected via gap junctions which allow ion flow.
How do the sino-atrial node cells perform their pacemaking ability?
They generate spontaneous action potentials of about 75 per minute which then travel throughout the heart, keeping the pace.
Where do the electrical impulses travel after leaving the sino-atrial node?
The pass along the atrial surfaces and to the atrio-ventricular node. They then pass through the interventricular septum along the bundles of His to the Purjinke fibres in the ventricles which rapidly conduct allowing synchronised contractions of the ventricles.
Why are action potentials conducted more slowly in the atrioventricular node?
The delay makes sure that the atria contract first so that the blood is pumped into the ventricles before their contraction, making blood circulation more efficient.
Describe the shape of a ventricular action potential.
The initial depolarisation is steep, it then plateaus before re-polarising.
What causes the initial sharp depolarisation?
It is caused by the opening of ‘fast’ voltage gated Na channels.
What gives the ventricular action potential its plateau shape?
‘Slow’ voltage gated Ca channels remain open after the initial depolarisation for some time. Their equilibrium potential of +120mV is what maintains the plateau of the action potential.
What causes the re-polarisation of the ventricular action potential?
Voltage gated Na channels open due to the depolarisation and this re-polarises the cell.
Describe the flow of K, Na and Ca ions during a ventricular action potential.
Na flows into the cell as voltage gated Na channels open.
Ca flows into the cell when the voltage gated Ca channels open.
K flows out of the cell when the voltage gated K channels open.
Why is the pacemaker current called the ‘funny’ current?
It is funny because instead of reacting to depolarisation, the cascade is triggered by hyperpolarisation caused by the opening of K channels of the previous AP.
What causes the inital depolarisation of the sino-atrial AP?
Slow Na channels open, causing a slow depolarisation unlike in the ventricular AP which is done by fast Na channels.
