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).
Alpha 2 Receptors. Alpha 2 receptors are located on secretory terminals of some postsynaptic adrenergic neurons. When these terminals secrete norepinephrine the neurotransmitter binds with these receptors as well as with adrenergic receptors on the other side of the synapse.The presynaptic neuron's response is to decrease the amount of NE being released -- it is a negative feedback mechanism.lpha 2 Receptors. Alpha 2 receptors are located on secretory terminals of some postsynaptic adrenergic neurons. When these terminals secrete norepinephrine the neurotransmitter binds with these receptors as well as with adrenergic receptors on the other side of the synapse.