Normal resting heart rates range from 60â100 bpm. Bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people and do not necessarily require special attention.achycardia is a fast heart rate, defined as above 100 bpm at rest. Bradycardia is a slow heart rate, defined as below 60 bpm at rest. During sleep a slow heartbeat with rates around 40â50 BPM is common and is considered normal.
The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine (noradrenaline) and epinephrine (adrenaline).
Serotonin-norepinephrine reuptake inhibitors (SNRIs) also inhibit the reuptake of serotonin. In addition, they inhibit the re-absorption of another neurotransmitter called nor-epinephrine. Just like serotonin is associated with positive feelings, nor-epinephrine is associated with alertness and energy.