Autonomic NS and CVS Flashcards
What are the sympathetic effects of the…
a) pupil of eye
b) Airways to the lungs
c) Heart
d) Sweat Glands
a) dilate
b) relax
c) Increase HR
d) Increase localized secretion
What transmitters and post-synaptic receptors are used in parasympathetic neurotransmission?
Pre ganglionic releases Ach into nicotinic Ach receptors which allow an influx of Na+ and efflux of K+ to propel the AP down the post-ganglionic neurone
The post-ganglionic neurone releases Ach at muscarinic (cholinergic) receptors at the target tissue
What transmitters and post-synaptic receptors are used in sympathetic neurotransmission?
What are the 2 exceptions to this?
Pre ganglionic releases Ach into nicotinic Ach receptors, postganglionic is usually noradrenergic and NA is released
Exception:
1. Sympathetic innervation to sweat glands is cholinergic (releases Ach to the target tissue) onto muscarinic receptors
- Chromaffin cells of the adrenal medulla recieve Ach input from the preganglionic and release adrenaline into the bloodstream
What are the largest ganglia in the ANS and where do they synapse and innervate?
2 coeliac ganglia, they synapse with post-ganglionic neurones in the upper abdomen and innervate most of the GI tract
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? What are they instead?
They respond to Ach, not NA and adrenaline. Therefore, they’re cholinergic
What is the significance of the medulla oblongata?
“Controls the CVS”: contains cardio-accelerator centre, cardio-inhibitor center, vasomotor centre
Where are the baroreceptors? What do they do?
Carotid sinus and aortic arch: They’re sensitive to stretch and can detect high pressures in arterioles, when activated (stretched) they send afferent messages to the medulla oblongata to vasodilate
Where are the atrial receptors? What do they do?
Sense low pressure in veins and R atrium
What is the region in which nerves are gathered that controls the sympathetic and parasympathetic output?
Solitary nucleus (in the medulla oblongata)
Explain how the VAGUS n influences the heart
Synapses with postganglionic cells on the epicardial surface or within the walls at the SA and AV node
Releases Ach at the M2 muscarinic receptors (inhibitory) to
1. Decrease HR
2. Decrease AV node conduction velocity
Explain how sympathetic nerves influence the heart
Postganglionic fibres arise from T1-T4 parts of the sympathetic chain and innervate the SA node, AV node and myocardium:
Release NA on B1 adrenoceptors to
1. Increase HR
2. Increase force of contraction
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?
a1 adrenoceptor
What type of adrenoceptor to coronary and skeletal muscle vessels also specifically have?
B2 adrenoceptors
What happens to pacemaker cells once NA has been released onto B1 adrenoceptors in the heart?
(2 things)
- Activates adenylyl cyclase which converts ATP – cyclic AMP
- Cyclic AMP is a ligand to HCN channels
- HCN channels allow more funny current (inward flow of Na+)
- Threshold is reached faster and Ca2+ channels for depolarisation
Therefore, the next AP is generated quicker and HR increases
In addition: Cyclic AMP activates PKA
- phosphorylation of calcium channels increase calcium entry during AP
- Increases Calcium-induced calcium release (sarcoplasmic reticulum)
- Increased force of contraction
How are pacemaker cells influenced parasympathetically?
2 things
- M2 receptors are inhibitory and decrease the production of cAMP - decreasing the action of HCN channels (as cAMP is a ligand for HCN channels), less funny current is allowed in, the threshold is reached slower and HR decreases
- K+ conductance is increased: so more K+ leaves the cell keeping the membrane potential negative despite the HCN channels allowing small influxes of Na+
Which adrenoceptor does adrenaline have a higher affinity for between B2 and A1? What is the overall effect?
Both sympathetic but adrenaline prefers
B2 adrenoceptors > a1 adrenoceptors
Therefore certain vessels will vasodilate easier with adrenaline rather than vasoconstrict.
What happens when a1 adrenoceptors in vessels are activated?
GQ pathway:
- phospholipase C activated – Release of IP3
- Increase in intracellular Ca2+ and influx of extracellular Ca2+
- Contraction of smooth muscle
What happens when B2 adrenoceptors in vessels are activated?
GS pathway:
Increases cAMP –> Activates PKA
1. Opens up K+ channels: keep the cell in hyperpolarisation
2. Phosphorylates and inactivates Myosin light chain kinase necessary for smooth muscle contraction
3. Smooth muscle relaxes - vasodilates
What can tissues do to ensure they receive enough perfusion?
Active tissues requiring blood flow will release vasodilatory metabolites into the blood which relaxes the surrounding smooth muscle and ensures perfusion
What do sympathomimetics do?
Mimic/modify actions of the sympathetic NS:
a-adrenoceptor agonists and b-adrenoceptor agonists
What is Dobutamine used for?
It’s a B1 agonist: increases HR
Name a B2 agonist drug and its action on the body
Salbutamol
Heart: vasodilator
Lungs (asthma): bronchodilator
