Question

I'm having a difficult time understanding alpha and beta receptors. Also the differences between Muscarinic and Nicotinic receptors. I was given an assignment to match what receptors cause what changes in the organs. I searched on ninja nerd and he only goes over alpha 1 and beta 2. HELP

Answer 1

Adrenalin and Acetylcholine are two major neurotransmitters in the nervous system. Dopamine, serotonin, GABA, Glycine, etc are some other neurotransmitters. Each exert their effects through several sub types of receptors. ACh is predominantly linked to parasympathetic responses while adrenergic receptors are linked to sympathetic nervous system.

Nicotinic and muscarinic receptors are subtypes of Acetylcholine receptors. The basic differences between them and their major locations are listed in the table below:

	Nicotinic Receptors	Muscarinic Receptor
	Central cholinoreceptor	Peripheral Cholinoreceptor
Signalling mechanism	Linked to ion channel	G-protein coupled receptor
Location	Excitatory	Excitatory or inhibitory
Locations	Autonomic Ganglia Stimulation(sympathetic and parasympathetic)	On all organs that receive postganglioninc parasympathetic fibers
	Adrenal Medulla - Release of Adrenalin and Noradrenalin	Heart - Inhibition (M2)
	Skeletal muscle contraction (at neuromuscular junction)	Exocrine Glands contraction (M3)
		Smooth muscle contraction (M3) - GIT, bronchi, urinary tract

A brief summary of the various functions of the Alpha and beta adrenergic receptors is given below:

Alpha 1	Alpha 2	Beta 1	Beta 2	Beta 3
Vasoconstriction	Inhibit release of norepinephrine	Tachycardia	Vasodilation	Adipose tissue
Increases peripheral resistance	Inhibit Ach release	Increase lipolysis	Slightly decreased peripheral resistance	Coronary vessels
Increased BP	Inhibit release of insulin	Increase contractility of myocardiu	Bronchodilation	Urinary bladder
Mydriasis		Increase release of renin	Increased glycogenolysis in liver and muscle
Increase closure of sphincter of bladder			Increased release of glucagon
			Relaxed uterine smooth muscle