Cardiovascular Physiology 21 Flashcards
What is resting autonomic tone?
The fact that both the sympathetic and parasympathetic systems are active at a steady background level
When will one system of the autonomic nervous system dominate?
When one fires at a rate above tonic level
Why are the Parasympathetic and Sympathetic systems on the heart considered extrinsic factors?
Because they originate outside the heart
What is responsible for initiating heart rate?
The conducting myocytes of the SA node
How does increases Sympathetic stimulation affect the pacemaker potential?
It increases the slope of the pacemaker potential (a faster depolarization to threshold)
How does sympathetic innervation increase the slope of the Pacemaker potential?
It increases F-type and T-type channel permeability
What do the F-type channels allow for?
Sodium to enter the cell
What do T-type channels allow for?
Calcium to enter the cell
What does an increase in permeability of F-type and T-type channels by the Sympathetic nervous system do?
Allows more positive to enter the cell allowing the SA node to reach threshold faster increasing the heart rate
How does Increase Parasympathetic stimulation of the SA node affect the slope of the Pacemaker potential?
It decreases the slope of the pacemaker potential causing a slower depolarization to threshold
How does Parasympathetic stimulation decrease heart rate?
- It decreases F-type channel permeability
* It increases potassium permeability
What does the decrease in F-type channel permeability by the parasympathetic nervous system do?
Reduces the movement of sodium into the cell decreasing the rate of depolarization
How does the increase in potassium permeability by the Parasympathetic nervous system decrease the heart rate?
Increased potassium permeability hyperpolarizes the cell making it harder to reach threshold because it is hyperpolarized
