What are the adrenergic and cholinergic systems, and how do they differ?

a) The adrenergic and cholinergic systems are the two main divisions of the autonomic nervous system, distinguished by their primary neurotransmitters and receptors.

• The adrenergic system primarily uses norepinephrine (noradrenaline) and epinephrine (adrenaline) as neurotransmitters. Its receptors are adrenergic receptors ($\alpha$ and $\beta$ subtypes). This system is largely associated with the sympathetic nervous system, mediating "fight or flight" responses like increased heart rate, bronchodilation, and vasoconstriction.

• The cholinergic system primarily uses acetylcholine as its neurotransmitter. Its receptors are cholinergic receptors (nicotinic and muscarinic subtypes). This system is largely associated with the parasympathetic nervous system, mediating "rest and digest" functions like decreased heart rate, bronchoconstriction, and increased gastrointestinal activity. It also functions at neuromuscular junctions and all autonomic ganglia.