Autonomic NS and CVS Flashcards
What transmitters and post-synaptic receptors are used in parasympathetic neurotransmission?
Pre-ganglionic releases Ach -> nicotinic Ach receptors ->
Postganglionic Ach -> muscarinic (cholinergic) receptors to target tissue
What transmitters and post-synaptic receptors are used in sympathetic neurotransmission?What are the 2 exceptions to this?
Preganglionic releases Ach -> nicotinic Ach receptors
Postganglionic releases NA
Exception:
1. Cholingergic innervation to sweat glands (Ach released to target tissue)
- Chromaffin cells recieve Ach from pre-ganglionic and release adrenaline into bloodstream
What are the largest ganglia in the ANS and where do they synapse and innervate?
2 coeliac ganglia: synapse with post-ganglionic neurones in upper abdomen and innervate most of GIT
What defines an adrenoceptor?
A G protein-coupled receptor that responds to NA and adrenaline: alpha 1+2 and beta 1+2
Why are muscarinic receptors not adrenoceptors even though they’re G protein-coupled receptors?
They are cholinergic (respond to Ach), not NA and adrenaline.
Briefly describe the action of baroreceptors, where are they located?
Carotid sinus and aortic arch:
Hypotension -> less pressure/stretch -> less baroreceptor firing -> increased sympathietic/decreased PS = vasoconstriction, increased HR/contractility/BP
Carotid massage/increased pressure -> (+) baroreceptors -> increased AV node refractory period/decreased HR and vasodilation
Where are the atrial receptors? What do they do?
R atria, sense low venous pressure
Where do receptors of the aortic arch and carotid sinus transmit PS innervation to?
Aortic arch -> VAGUS
Carotid sinus -> CN IX
-> solitary nucleus (in medulla oblongata)
Explain how sympathetic nerves influence the heart
Postganglionic fibres from T1-4 -> release NA on B1 adrenoceptors -> increase HR and FOC
What are the 2 types of Ca2+ channels in a pacemaker cell?
T Type: initiate depolarisation
L Type: open for the main upstroke
What type of adrenoceptor do most arteries and veins have vs skeletal and coronary muscle? Which is more common
Vessels/veins: a1
Skeletal/coronary muscle: b2
b2>a1
What happens to pacemaker cells once NA has been released onto B1 adrenoceptors in the heart? (2 things)
Activates adenylyl cyclase (ATP - cAMP)
cAMP is ligand to HCN channels -> more funny current -> faster AP -> (+) HR
cAMP -> PKA -> phosphorylation of calcium channels increase calcium entry during AP -> CICR -> (+) FOC
How are pacemaker cells influenced parasympathetically? (2)
M2 receptors inhibitory:
1. decrease cAMP -> less HCN channel action -> lower HR
- Increased K+ conductance: MP stays (-) despite HCN channels allowing small Na+ influxes
Which adrenoceptor does adrenaline have a higher affinity for between B2 and A1? What is the overall effect?
B2: vasodilation easier than vasoconstriction
What happens when a1 adrenoceptors in vessels are activated?
GQ pathway:
Phospholipase C -> PIP2 dissociates into IP3 and DAG
- IP3 increases Ca2+ influx from SER
- DAG -> PKA
=increased intracellular Ca2+ -> sm muscle contraction
What happens when B2 adrenoceptors in vessels are activated?
GS pathway:
Increased cAMP -> (+) PKA
- Opens K+ channels -> cell stays hyperpolarisation
- Phosphorylates and inactivates myosin light chain kinase necessary for smooth muscle contraction
=vasodilation
What is Dobutamine used for?
B1 agonist: increases HR
Name a B2 agonist drug and its action on the body
Salbutamol
Heart: vasodilator
Lungs (asthma): bronchodilator
What does chronotropic and inotropic mean? Which input and receptor do both of these things?
Chronotropic: Increase HR
Inotropic: increase FOC
NA on B1 receptors in heart pacemaker cells
Which ion are HCN channels sensitive to? (other than Na+)
K+: Repolarisation (less k+) -> (+) HCN
*less intracellular K+ means MP becomes more (-), so HCN channels allow more Na+ influx to bring MP back up
Which vessels have B2 and A1 adrenoceptors?
Liver, skeletal muscle, myocardium
Name one muscarinic agonist and one antagonist
Agonist: pilocarpine
Antagonist: Atropine
When should and shouldn’t you give propanolol?
Propanolol is a non-specific B1 AND B2 antagonist:
- decreases HR and FOC (antagonizing B1)
- bronchoconstriction (antagonizing B2) = don’t give in asthma
When could you give adrenaline?
Anaphylactic shock