What is a normal heart rate for healthy adults at rest, and what neural inputs c

Normal heart rate for a adult at rest is anywhere from 60 to 100 BPM, there are a lot of factors that can contribute to this. Example if the person is an athlete they will have a significantly lower heart rate. Electrolyte levels, primarily Potassium. Is the person dehydrated, overhydrated. Did they just eat? Any preexisting condition?

A normal resting heart rate for adults ranges from 60 to 100 beats a minute.
Many factors can influence heart rate, including:

-Activity level
-Fitness level
-Air temperature
-Body position (standing up or lying down, for example)
-Emotions
-Body size
-Medications

When all nervous system input to the heart is blocked,heart rate increases to about 100 bpm.
In the normal resting conditions the vagal tone (the constant activity of the vagus nerve) keeps the heart rate at what it stays normally around 60-80 bpm.
During stressful conditions, the sympathetic activity tends to increase heart rate to much more over 100bpm.
If all the input is severed, then due to the removal of the constant effect of vagal tone, the HR rises and stays around 100 bpm.

The normal resting heart rate is 60-100 beats per minute (BPM), although trained athletes often have slower heart rates have slower heart rates at rest.  The autonomic division modulates heart rate, heart rate is based upon factors of health and fitness, as well trained athletes have a slower heart rate on average, another factor may be if someone is anxious or excited as heart rates can reach 125 BPM or higher. Age may also be a factor as children tend to have higher heart rates than adults. Heart rate is initiated by autorhythmic cells in the SA node, but it is modulated by neural and hormonal input. The sympathetic and parasympathetic branches of the autonomic division influence heart rate through antagonistic control. Parasympathetic activity slows heart rate while sympathetic activity speeds it up.  Sympathetic neurons secrete norepinephrine which cause a sodium and calcium ion influx, increasing rate of depolarization and thus, increasing heart rate. Parasympathetic neurons secrete Acetylcholine which increases potassium ion influx but decreases calcium influx which causes cells to become hyperpolarized and rate of depolarization decreases, causing a drop in heart rate.  Normally, tonic control of the heart rate is dominated by the parasympathetic branch. This control can be shown by blocking all autonomic input to the heart. The spontaneous depolarization rate of the SA node is 90-100 BPM. To achieve the average of 70 BPM, tonic parasympathetic activity must slow the intrinsic rate down from 90 BPM.

Silverthorn, D.U. (2013). Human Physiology, An Integrated Approach. 6E: 487,495-497.