TOPIC 2 - The ANS Flashcards
What is the genral organisation of the ANS?
CNS –> Peripheral ganglion –> Taregt cell
Preganglionic neuron –> peripheral ganglion –> target cell
The adrenal medulla is an exception in the sympathetic pathway. what do chromaffin cells do?
Chromaffin cells release mainly adrenaline (epinephrine) (and noradrenaline ).
what is the function of preganglionic neurons?
Are always cholinergic fibres so release ACh acetylcholine as their primary neurotransmitter.
ACh activates nicotinic ACh receptors on the postsynpatic cell.
What is the difference between the sympathetic and parasympathetic system?
Sympathetic:
- fight or flight
- short cholinergic preganglionic neurons
- long adrenergic postganglionic neurons.
- Target tissues express alpha and beta adrenergic receptors
Parasympathetic:
- Rest and digest
- long cholinergic pregnaglionic neurons
- short adrenergic postganglionic neurons
- target tissue expresses muscarinic ACh receptors.
What 2 else regulates ANS output?
Forebrain and visceral afferents.
What receptors do acetylcholine and noradrenaline act upon?
- nAChR nicotinic receptors
- mAChr muscarinic receptors
- a- and b-adrenoreceptors.
what does curare do?
Curare binds to acetylcholine receptors and can block effects of nictotine and acetylcholine on nicotinic receptors.
What are muscarinic receptors?
Muscarinic receptors have 5 types M1-5 which are G-protein coupled receptors. They recognise acetylcholine.
What does atropine do?
Atropine antagonises and blocks the effects of muscarinic actions (parasympathetic).
Explain the difference between the muscarnic receptors 1-5.
M1, M3, M5 = odd receptors are coupled to Gq type proteins.
M2 and M4 = even receptors are coupled to Gi inhibitory G protein - which inhibits adenylyl cylase so decreases second messenger cAMP. Activation of these receptors, activated the GIRK (potassium channels), so switches these on and also cause inhibition of voltage gates calcium channels.
What do M2 receptors do?
M2 receptor agonists which activate GIRK potassium channels and inhibit L-type calcium channels.
- M2 receptors are coupled to adenylyl cyclase through Gi - inhibts enzyme adenlylcycalse so decreases cAMP which inhibits the opening of L-type Ca 2+ channels, so decreases the contractility.
- M2 receptors mediate the effects of pilocarpine and slows heart rate - by opening GIRK (potassium channel).
What do M1 and and M3 receptors do?
Gq coupled receptors.
Activating Gq receptors will increase calcium, so stimulate the contraction of smooth muscle.
What is glaucoma and how is it treated?
glaucoma occurs when drainage tubes within the eye becomes slightly blocked. Prevents eye fluid from draining properly causing increased pressure that can damage the optic nerve.
Pilocarpine eyedrops treats glaucome - reduces pressure in eye so fluid can be drained from eye.
drugs can be used to enhance cholinergic transmission - cholinomimetric - e.g anticholinesterase drugs. how do these work?
They inhibit the enzyme acetyl cholinesterase as indirectly increases levels of acetylcholine which increases activation of cholinergic receptors.
Mutiple subtypes of adrenoreceptors include B1 and B2. what do they do?
B1 in heart increases heart rate (tachycardia) and increased contractility (as is a Gs coupled receptor).
B2 in bronchi - causes relaxation
