Autonomic Nervous System Flashcards
To what degree of myelination are the pre- and post-ganglionic fibres?
Pre-ganglionic = small myelinated Post-ganalionic= unmyelinated
Name some structures that ANS neurones effect?
Smooth muscle
Cardiac muscle
Glands
GI neurones
What are the 2 divisions of the ANS?
Sympathetic (fight or flight)
Parasympathetic (rest and digest)
What regions of the spinal cord to sympathetic nerves originate?
Thoracic T1-12
Lumbar L1-2
What is convergence?
Many preganglionic fibres synapsing onto one postganglionic fibre
What is divergence?
One preganglionic fibre synapsing onto several postganglionic fibres
What type of receptors does Acetylcholine work on?
Cholinergic - nicotinic or muscarinic
What type of receptor does Noradrenaline work on?
Adrenergic - alpha and beta receptors
What do preganglionic fibres release during sympathetic nervous system and what receptor does it act on?
Acetylcholine on Nicotinic receptors
What do postganglionic fibres release and what receptor do they act on during sympathetic system?
Noradrenaline on alpha or beta receptors
What cells have no axons but release adrenaline and noradrenaline into the blood?
Postganglionic cells of the adrenal medulla
What do preganglionic fibres release and what receptors do they act on during the parasympathetic system?
Acetylcholine on nicotinic receptors.
What do postganglionic fibres release and what receptors do they act on during parasympathetic system?
Acetylcholine on muscarinic receptors
Give some effects that the sympathetic system produces?
Airways dilate Heart beats faster Heart beats stronger Blood goes to muscle Gut motility decreases Gut enzyme secretion inhibited Stored energy is released Pupils dilate Eyes focus far away Hair stands on end Mouth gets dry
Give some effects the parasympathetic system produces?
Airways constrict Heart beats slower Heart beats weaker Blood goes to gut Gut motility increases Gut enzyme secretion is stimulated Energy is stored Pupils construct Eyes focus close up Hair lies flat Mouth starts drooling
What receptors relax smooth muscle?
Beta -2
What receptors contract smooth muscle?
Alpha -1
Name the beta -2 agonist that dilates airways but does not affect the heart?
Salbutamol
What does the parasympathetic system do to blood vessels?
Usually has no effect
Give an example of single innervation?
Only the sympathetic system acts on energy stores, the parasympathetic system has no effect
Give an example of dual innervation with non-antagonistic actions?
Sympathetic system stimulates thick secretions from salivary glands that are rich in enzymes.
The parasympathetic system also stimulates salivary secretion but it produces a watery secretion.
Give an example of dual innervation with complementary effects?
Sympathetic system contracts smooth muscle in reproductive tract and causes ejaculation.
Parasympathetic system relaxes smooth muscle in reproductive tract and causes erection.
What controls all of these responses?
Autonomic reflexes
Eg baroreceptor reflex detects blood pressure.
Central control via hypothalamus
Describe the process of synaptic transmission?
Synthesis and packaging of transmitter into vesicles
Na+ action potential invaded terminal
Activates voltage gated Ca2+ channels
Triggers exocytosis of vesicles
Transmitter diffuses across cleft and binds to postsynaptic receptors
Pre-synaptic autoreceptors inhibit further transmitter release.
Transmitter is inactivated by uptake into glia or neurones
Transmitter is metabolised
At a somatic synapse what drug can be used to inhibit choline transporters?
Hemicholinium
At a somatic synapse what drug can be used to Block voltage gated Ca2+ channels?
Black widow spider venom.
What drugs can block vesicle fusion at somatic synapses?
Botulinium toxins.
Give an example of a non-depolarising nicotinic receptor blocker at somatic synapses?
D-tubocurarine.
What drug could be used to prolong the AP at somatic synapses?
3,4-aminopyridine.
What drug blocks acetylcholinesterase at somatic synapses?
Eserine.
What are anti-cholinesterases used for clinically?
Treating myasthenic syndromes.
Reversing action of non-depolarising blockers.
Countering botulinum poisoning.
What blocks ACh activated channels in ganglionic transmission?
Hexamethoneum.
What is a non-depolarising nicotinic receptor blocker of the ganglionic transmission?
Mecylamine.
What is a depolarising nicotinic receptor blocker of ganglionic transmission?
Suxamethoneum.
How could you increase transmission at ganglionic synapses of autonomic pathways?
Activate nicotinic receptors (eg nicotine, is more potent at ganglia than NMJ, N1>N2 receptors).
What are the potential sites of action at post-ganglionic parasympathetic synapses?
Muscarinic receptor antagonists (eg atropine).
Muscarinic receptor agonists (eg carbachol, pilocarpine).
What do muscarinic agonists do?
Mimic the effect of the parasympathetic system.
What do muscarinic antagonists do?
Block effects of the parasympathetic system.
What drugs will block the enzymes that produce NA at post-ganglionic sympathetic synapses?
Carbidopa.
Give an example of a drug that blocks the transporter that fills the vesicles with NA at post-ganglionic sympathetic synapses?
Reserpine.
What drugs block α or β postsynaptic receptors?
Doxazosin.
Propranolo.
What are potential sites for action to make post-ganglionic sympathetic synapses to work better?
Stimulate NA adrenaline release (eg amphetamine).
Inhibit uptake into neurones (eg cocaine & tricyclic antidepressants) or glia (eg phenoxybenzamine).
Activate postsynaptic receptors (eg phenylephrine and salbutamol).
