Session 4 - CNS and ANS Flashcards
What are ganglia?
-Collections of cell bodies within the PNS
What is a neuro-effector junction?
-A synapse between a post-ganglionic neurone and an effector cell
Where do the sympathetic and parasympathetic nervous systems leave the spinal cord?
- Sympathetic from Thoracic and Lumbar regions
- Parasympathetic from Cranial and Sacral regions
Which division of the ANS has long pre-panglionic fibres and short postganglionic fibres?
-Parasympathetic
Which division of the ANS has short pre-ganglionic fibres and long post-ganglionic fibres?
-Sympathetic
Where are most of the ganglia of the sympathetic nervous system located?
-Paravertebral chain
Where are most of the ganglia of the parasympathetic nervous system located?
-Close to or within their effector structures
Which fibres and of which divisions have Ach as its neurotransmitter?
-Preganglionic fibres of both divisions and post ganglionic of parasympathetic
What is the neurotransmitter of the post-ganglionic fibres of the sympathetic nervous system?
-Noradrenaline
What receptors are on post-ganglionic cell bodies?
-Nicotinic Ach receptors
What receptors are found on effector cells of the parasympathetic system?
-Muscarinic 1,2,3 Ach R
What receptors are found on the effector cells of the sympathetic nervous system?
-a and b adrenergic receptors
Which functions are an exception to the sympathetic nervous system?
-Perspiration and Ejaculation which use Ach and muscarinic receptors
What type of receptor are muscarinic receptors?
-GPCR
What type of receptors are nicotinic receptors?
-Fast-acting ion channels
What type of receptors are adrenoreceptors?
-GPCR
How does the sympathetic innervation of the adrenal medulla differ from the rest?
-Has specialised post-ganglionic neurones called chromaffin cells which secrete adrenaline when stimulated
Whyat effect does the ANS have on the CVS?
-Controls HR, force of contraction and vasomotor tone
Through what nerve does parasympathetic input to the heart occur?
-Vagus
What neurotransmitter and receptors does the parasympathetic NS use to innervate the heart?
- Ach
- M2 receptors
What effect does the parasympatheric nervous system have on the heart?
- Decrease rate
- Decrease AV node conduction velocity
What structures does the sympathetic NS innervate in the heart?
- SA node
- AV node
- Myocardium
What receptors does the sympathetic nervous system act on in the heart?
-B1-adrenoreceptors
What effect does the sympathetic nervous system have on contraction?
- Increase rate
- Increased force
How does the sympathetic NS increase HR?
- Increases depolarising slope of funny current by stimulating b1-adrenoreceptors
- b1-adrenoreceptors -> Gas dissociates and activates adenyl cyclase -> this increases cAMP production in the cell which is a cyclic nucleotide
- cAMP activates more HCN channels increasing the speed of depolarisation, with a resulting increase in hyperpolarisation both increasing the HR
How does the parasympathetic NS decrease HR?
- Ach stimulates M2 receptors which have an associated Gai subunit
- Gai inhibits adenyl cyclase which decreases cAMP -> decreased activation of HCN
How are the divisions of the ANS arranged?
-Two neurones arranged in series with the pre-gangionic neurone having its cell body in the CNA and the post-ganglionic cell neurone having its body in the PNS
The parasympathetic NS increases the conductance of K+ in cels, so why is there an overall decrease in HR?
-The decrease in cAMP has a greater effect than the increased hyperpolarisation caused by increased K conduction
How does NA (from SNS) increase the force of contraction of the heart?
-NA binds to b1-adrenoreceptors
-This activates the GPCR and Gas dissociates from the G protein and activates AC. This increases the production of cAMP with a resultant activation of PKA
-PKA results in the phosphorylation, and thus opening of Ca channels, causing increased entry of Ca during the AP
-NA increases the uptake of Ca into the SR -> more to be released
-NA causes increased sensitivity of contractile machinery to Ca
These cause an increased force of contraction
Which type of innervation do most blood vessels get? What is the exception to this?
- Sympathetic
- Erectile tissue which gets parasympathetic
What type of adrenoreceptor do most arteries and veins have?
-a1-adrenoreceptors
Which blood vessels have a1 and b2 adrenoreceptors?
- Coronary vessels
- Skeletal muscle vasculature
What is the result of a decreased sympathetic output to blood vessels?
-Vasodilatation
For those vessels which have B2 and a1-adrenoreceptors, which neurotransmitter does each of them respond to?
- a1-> circulating noradrenaline
- b2->circulating adenaline
Why can adrenaline cause vasodilation of some vessels?
- Adrenaline acts on b2-adrenoreceptors in coronary or skeletal musche vessels
- B2 adrenoreceptor has Gas-type gprotein
- Gas dissociates and activates adenyl cyclase
- Increased cAMP production
- Increased activation of PKA which Increases conduction of K+
- Inhibits MLCK and causes reduced contraction of smooth muscle as myosin head not phosphorylated
How does noradrenaline cause vasoconstriction of vessels?
- NA acts on a1-adrenoreceptor
- a1 has Gaq gprotein, gaq dissociates and activates PLC
- PLC cleaves PIP2 into IP3 and DAG
- IP3 acts on IP3 receptors on SR causing increased calcium release -> contraction can then occur
- DAG stimulates PKC which inhibits MLCP further influencing contraction as inhibition of MLCP causes increased phosphorylation of MLC
What role do local metabolites have in vasodilation?
- Metabolising tissues produce metabolites such as adenosine, H+, K+,increased pCO2
- This local accumulation has a strong vasodilator effect
Why is metabolites causing vasodilation so important?
-Allows supply to meet demand ensuring adequate perfusion as highly active tissues will produce lots of metabolites -> high vasodilatation -> increasd bloodflow
Where are baroreceptors?
-Aorta and coronary sinus
What are baroreceptors?
- Nerve endings which are sensitive to stretch detect increases in arterial pressure and relay the information through afferent fibres to the medulla
- The medulla can then cause bradycardia and vasodilation through efferent pathways to decrease bp
What are sympathomimetics?
-Drugs which are a and b adrenoreceptor agonists, and thus mimic the effect of the sympathetic nervous system
How does the administration of adrenaline restore function in cardiac arrest?
-Pharmalogical levels of adrenaline act on a1-adrenoreceptors on vessels causing vasoconstriction and increasing cardiac output
-What is dobutamine?
-A b1-agonist which is used in cardiogenic shock to increase the force and rate of contraction
How does adrenaline treat anaphylactic shock?
- During anaphylaxis there is widespread vasodilation
- Adrenaline acts on a1-adrenoreceptors and causes vasoconstriction through Gaq-> PLC-> IP3-> increased Ca-> contraction
Why is salbutamol used to treat asthma?
- Activates b2-adrenoreceptors
- Gas dissociates and activates adenyl cyclase
- Increased cAMP-> increased PKA
- PKA phosphorylates MLCK leading to its inhibition
- Myosin not phosphorylated
- Contraction cannot occur
- Bronchi relax
How can a-adrenoreceptor antagonists be used in the treatment of hypertension?
- Antagonist binds to a1-adrenoreceptor and prevents NA binding
- Prevents vasoconstriction so vasodilatation occurs
- Lowers pressure
Name an anti-hypertensive agent which works as an a-adrenoreceptor antagonist
-Prazosin
What is propranolol?
-Non-selective Breceptor antagonist which slows HR and reduces force of contraction by blocking b1 receptors, but also causes bronchoconstriction by blocking B2 receptors in the bronchi
What is atenolol?
-Selective b1 receptor antagonist
What is pilocarpine?
-Muscarinic agonist used in the treatment of glaucoma as it activates constrictor pupillae muscle
What is atropine?
-Muscurinic antagonist used to increase HR by blocking the parasympathetic innervation of the heart through M2 receptors
