Concept Check

• The sympathetic and parasympathetic branches of the autonomic nervous system have different effects on nodal tissues within the heart. What are these effects?

  Sympathetic neurons release norepinephrine (NE), which increases both the heart rate and force of contraction through stimulation of beta receptors on nodal cells and contractile cells. Parasympathetic neurons release acetylcholine (ACh), which decreases both the heart rate and the force of contraction by stimulating muscarinic receptors on nodal cells and contractile cells.