Flashcards in The Autonomic NS Deck (33):
What is the origin of the parasympathetic NS?
Cranio-sacral (cranial nerves III, VII, IX and X and S2-S4)
What do the preganglionic neurones of the ANS release and which receptors does it act on?
Acts on nicotinic ACh receptors
What do postganglionic neurones release and which receptors do they correspond with?
Sympathetic: releases noradrenaline which acts on adrenergic receptors
Parasympathetic: releases acetylcholine which acts on muscarinic receptors
What is the sympathetic exception?
The sympathetic innervation releases ACh which acts on muscarinic receptors
What is the mode of action of both types of ACh receptor?
Muscarinic = G protein coupled
Nicotinic = integral ion channel
Under basal conditions, which NS is more dominant?
Which receptors are located in the lungs and what do they activate?
Beta 2 = relaxation (SNS)
M3 = contraction/constriction of airways (PNS)
Which receptors does salbutamol act on?
Beta 2 adrenoreceptors in the lungs
What receptors occur in the heart and what do they activate?
Beta 1 = increase rate and force of contraction (SNS)
M2 = decrease rate (PNS)
Which parasympathetic nerve innervates the heart and where does it synapse?
Vagus nerve (cranial nerve X)
Synapses at the epicardial surface or SAN and AVN
Where does the sympathetic NS synapse in the heart?
SAN, AVN and myocardium
What do we call an effect that changes heart rate?
What do we call an effect that changes force of contraction?
What kind of receptor is the beta 1 adrenoceptor in the heart?
G protein coupled (G alpha s)
What is the mode of action of the beta 1 receptors to increase HR?
Stimulates adenyl cyclase to increase production of cAMP
cAMP is a cyclic nucleotide therefore more HCN channels open
Speeds up pacemaker potential therefore APs fire sooner
What type of receptor is the M2 receptor in the heart?
G protein coupled (G alpha i)
What is the mode of action of M2 receptors to decrease HR?
Inhibit adenyl cyclase to decrease production of cAMP
Less HCN channels are opened
Increase in K+ conductance
Takes the potential further from threshold so takes longer to fire an AP
How do beta 1 receptors in the heart act to increase force of contraction?
Increased production of cAMP
PKA phosphorylates calcium channels to increase calcium entry
Which are the only 2 types of vasculature to have beta 2 adrenoceptors as well as alpha 1?
Coronary and skeletal muscle vasculature
What is vasomotor tone?
A basal level of sympathetic output acting to keep the vessels at a particular width.
How does the body dilate and constrict blood vessels?
Dilate: decrease sympathetic output
Constrict: increase sympathetic output
Which receptors does adrenaline have a higher affinity for?
Has a higher affinity for beta 2 receptors than alpha 1 receptors
What is the mode of action of beta 2 receptors causing vasodilation?
Increased production of cAMP
Increased activation of PKA
Opens K+ channels and inhibits MLCK so contraction cannot occur
What is the mode of action of alpha 1 receptors to cause vasoconstriction?
Phospholipase C activation
IP3 binds to receptors on intracellular calcium stores
Increase in intracellular calcium
Bind to CaM and regulates MLCK to allow contraction
Give examples of metabolites with vasodilator effects
What types of drugs are sympathomimetics?
Alpha adrenoceptor agonists
Beta adrenoceptors agonists
Adrenaline is a sympathomimetic administered for what?
What would alpha 1 antagonists be used for and why?
Dilate vessels as blocks NA binding to alpha 1 receptors
What would we use beta adrenoreceptor antagonists for?
Decreasing heart rate
Why is atenolol better than propranolol?
Atenolol is selective to beta 1 receptors (cardio-selective) whereas propranolol acts on beta 1 and beta 2 receptors. This means propranolol will cause bronchoconstriction as well as decreasing HR.
What are muscarinic agonists used for?
Activates constrictor pupillae muscle to reduce the pressure in the eye
What are muscarinic antagonists used for?
Dilation of pupils