13. Modulating pacemaker rate

The autonomic nervous system can change the rate at _ without _.

which pacemaker cells reach threshold, replacing their intrinsic rhythm

Sympathetic input can _ and can increase the _. Either change lets the cell _.

raise the pacemaker-cell membrane potential, slope of the pacemaker potential, reach threshold sooner and increases heart rate

A shorter interval between pacemaker action potentials produces a _.

higher contraction frequency in the connected cardiac muscle.

The heart therefore has an _ but remains adjustable by inputs from the brain and _ nervous system

intrinsic rhythm, autonomic