Alpha-2 Receptors etc.

In the lecture I was a bit short on explaining issues regarding these receptors: The classification of such receptors of course is based on struture-activity studies, eventually confirmed by molecular biology/cloning. Initially these were seen to function as pre-synaptic receptors whose stimulation by norepinephrine (NE)  reduced NE discharge and thus represented a self-regulatory process. Later it was found that agonists of alpha-2 receptors were present in many tissues and functioned sometimes independent of innervation/neurotransmission pathways, both in the periphery and centrally. You just should be aware of this in principle, and you don't have to memorize the long list of individual functions I copied from theWikipedia:

• decrease release of acetylcholine
• decrease release of norepinephrine
• Inhibit norepinephrine system in brain
• inhibition of lipolsis in adipose tissue
• inhibition of insulin release in pancreas
• induction of glucagon release from pancreas
• platelet aggregation
• contraction of sphincters of the gastrointestinal tract
• ↓ Secretion from salivary gland
• relax gastrointestinal tract (presynaptic effect)
• decreased aqueous humor fluid production from the ciliary body 

I am sure you are glad we are not telling you to remember this at this time!