Regulation of Heart Rates

The brain's cardiovascular center activates the ANS based on inputs received from sensory receptors.

For example, proprioceptors in muscles and joints sense changes in body position, and baroreceptors inside blood vessels detect changes in blood pressure.

Once activated, the ANS releases hormones and neurotransmitters to regulate heart rate.

The sympathetic division of the ANS increases the heart rate during emotional and physical stress.

It promotes norepinephrine release, accelerating depolarization in the SA and AV nodes. Further, physical activity or stress stimulates the adrenal medullae to release epinephrine and norepinephrine, increasing the heart rate.

The parasympathetic division of the ANS predominates at rest and reduces the heart rate. It acts via the release of acetylcholine, slowing the spontaneous depolarization in the SA and AV nodes.

In addition, conditions like hypoxia, acidosis, and alkalosis can depress cardiac activity.

Ion concentrations also affect cardiac function. High blood potassium and sodium lower heart rate and contractility, while more intracellular calcium raises it.

Lastly, age and sex also influence heart rate. Babies and adult females typically exhibit higher heart rates.