Final answer:
The intrinsic rate of the SA node, which is the natural pace without autonomic nervous system input, is c. 60-100 beats per minute (bpm).
Step-by-step explanation:
The intrinsic rate of the SA node is c. 60-100 bpm. The sinoatrial (SA) node, often termed the pacemaker of the heart, has an inherent rhythm that dictates the normal heart rate. Without any modulation by the autonomic nervous system, this rate would hover around 100 bpm.
However, the parasympathetic nerves, which usually predominate over sympathetic input at rest, apply a slowing effect, resulting in a normal resting heart rate in the region of 60-80 bpm. Extensive physical activity or stress would engage the sympathetic nerves, potentially raising the heart rate significantly above 100 bpm, but the baseline intrinsic pace of the SA node itself is within that 60-100 bpm range.