Cardiovascular Physiology Flashcards
What is the resting potential of cardiac pacemaker cells?
-55 to -60
What is the stimulus for the cardiac pacemaker action potential generated by, at what level does depolarisation occur?
Na funny channels which slowly leak into the cell. When they reach a threshold the n L-type calcium channels open and cause the action potential. depolarisation is at -40mV.
How does the site of innervation of the PNS and SNS differ in the heart?
The PNS tends to impact nodal function whereas the SNS affects all areas.
Mechanism of PNS slowing heart rate
Act increases the permeability to potassium ions. These will leak out of the cell and cause the membrane potential to become more negative.
What effects does sympathetic stimulation have on the heart?
Increases nodal firing rate
Increases conductibility throughout all areas of the heart
Increases strength of contraction
What is the mechanism by which SNS has its cardiac effects?
It likely increases permeability to Na and Ca ions.
Which division of the circulation is not innervated by the sympathetic nervous system?
Capillaries (although pre-capillary sphincters and met arterioles may be innervated).
Where, anatomically, is the vasomotor centre located?
In the medulla and lower third of the pons.
Equation that predicts venous return.
