-Action potentials are conducted more slowly from the atria to the ventricles.
Table 3-1. Autonomic Effects on the Heart and Blood Vessels
Conduction velocity (AV node)
ßi i (atria only) Muscarinic
Vascular smooth muscle
Constriction a, Constriction a, Relaxation p2
AV = atrioventricular.
- The mechanism is decreased inward Ca2+ current and increased inward K+ current.
3. Sympathetic effects on heart rate and conduction velocity
- Norepinephrine is the neurotransmitter, acting at pi receptors.
a. Positive chronotropic effect
-increases heart rate by increasing the rate of phase 4 depolarization.
- More action potentials occur per unit time because threshold potential is reached more quickly and more frequently.
- The mechanism is increased If, the inward Na+ current that is responsible for phase 4 depolarization in the SA node.
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