ANS Flashcards
Which neurotransmitter is released at the parasympathetic first synapse?
Acetylcholine
Which type of receptor accepts the neurotransmitter at the parasympathetic first synapse?
Nicotinic ACh
Which neurotransmitter is released at the parasympathetic second synapse?
Acetylcholine
Which type of receptor accepts the neurotransmitter at the parasympathetic second synapse?
Muscarinic ACh
Which neurotransmitter is released at the sympathetic first synapse?
Acetylcholine
Which type of receptor accepts the neurotransmitter at the sympathetic first synapse?
Nicotinic ACh
Which neurotransmitter is released at the sympathetic second synapse?
Noradrenaline
Which type of receptor accepts the neurotransmitter at the sympathetic second synapse?
Alpha & beta adrenoreceptors
Which axon is longest in the parasympathetic nervous system?
Presynaptic (synapses near target organ)
Which axon is longest in the sympathetic nervous system?
Postsynaptic (synapses in sympathetic trunk = runs next to spinal cord)
Name two target organs purely innervated by only Sympathetic or the parasympathetic nervous system
Sweat glands
Blood vessels
(SYMPATHETIC)
Name 3 organs innervated by both the sympathetic and parasympathetic nervous system but the parasympathetic innervation predominates
GIT
Bladder
Salivary glands
What is the effect of the parasympathetics on the heart?
Slows
What is the effect of the sympathetics on the heart?
Fast
Name an organ in which the parasympathetics and sympathetics work together
Salivary glands
What are the 3 different types of G proteins?
q
s
i
What is a varicosity?
Sites where synapses occur along an axon = bulges out
1 in how many presynaptic action potentials cause a release?
50
Which types of receptors are located at ganglionic synapses?
Inotrophic (ligand gated ion channels = acivated by 2 ACh = conformational change)
What type of receptors are found at post ganglionic synapses?
Metabotrophic (GPCR) = changes what goes on inside cell
What is the action of displacing agents?
They displace the NA from the synapse (displaces it from the varicosity)
- competes with NA for uptake 1 (decrease reuptake of NA)
- competes with NA for vesicular transporters
- more NA in varicosity (reverse uptake 1 = Na & NA move out)
What is pephedrine used for?
= displacing agent
- reverse hypotension after epidural anaesthesia
- decongestant nasal drops (vasoconstriction of mucosal blood vessels)
What is pseudoephedrine used for?
Systemic nasal decongestant (in sprays, sudafed, lemsip & claritin D)
= displacing agent
n.b. some sudafeds and lemsips contain phenylephrine instead
What is the action of amfetamine, metamfetamine & ecstacy at the CNS?
Cause severe hypotension
What foods is tyramine found in?
mature cheese
pickled herring
broad bean pods
marmite
What does tyramine cause?
High blood pressure
Sweating
What happens when you give a person already taking a drug to increase snaptic [NA] a displacing agent too?
Hypertensive crysis
= hypertension, tachycardia (/reflex bradycardia)
In which situations is methyldopa the preferred anti-hyertensive?
When other treatments have failed
In pregnancy
What are the 2 different methods of action for methylopa as an anti-hypertensive?
Alpha 2 adrenoreceptor agonist
- inhbits NA exocytosis (also competes with NA & enters variosity through uptake 1 -> into vesicles => methyldopamine => methylNA
- reduces sympathetic drive to CNS -> crosses BBB = inhibits/reduces firing of SNS = decreased [NA] at synapses
What does guanethidine do?
Noradrenergic neurone blocking drug
= rapid control of blood pressure in hypertensive emergency (depletes nerve endings of NA = no longer work)
VERY SEVERE SIDE EFFECTS
SYMPATHETICS
Which receptors are the most prevalent in the heart?
Beta 1 adrenoreceptors
(sympathetics)
SYMPATHETICS
What is the effect of the SNS on the heart?
Increased rate and contractility
SYMPATHETICS
Which receptors are involved in constant sympathetic tone of the blood vessels?
Alpha 1 adrenoreceptors
SYMPATHETICS
Why are beta 2 receptors in blood vessels not activated by NA from nerves?
They are extrasynaptic
SYMPATHETICS
Which type of adrenoreceptors does circulating adrenaline (e.g. from stress) have a greater effect on?
Beta
(n.b. effect it concentration dependant)
SYMPATHETICS
With a low circulating adrenaline level which receptors are activated?
And what is their effect?
Beta 2
Vasodilation
(activates adenyl cyclase = increase cAMP = inhibits myosin light chaine kinase = less contraction)
SYMPATHETICS
With a high circulating adrenaline level which receptors are activated?
And what is their effect?
Alpha 1
Vasoconstriction
= activates phospholipase C = IP3 = increased intracellular Ca = contraction
SYMPATHETICS
What are the main type of receptor in the lungs?
Beta 2 adrenoreceptors
SYMPATHETICS
What are the lungs beta 2 adrenoreceptors activated by?
Circulating adrenaline or beta 2 agonists
SYMPATHETICS
When the lungs beta adrenoreceptors are activated what happens to the lungs?
Brochodilation
PARASYMPATHETICS
What happens when muscarinic receptors are stimulated?
- Exocrine secretions = increased in salivary glands, GI tract, lacrimal & sweat glands
- Smooth muscle = mainly contract (excluding blood vessels)
- Heart = mostly inhibitory (hyperpolarisation via Gi)
- ACh release from parasympathetic varicosities (inhibits Ca channels)
- Vasodilation (NO from endothelial cells)
What are the side effects of inhibition of muscarinic receptors?
- Restlessness
- Agitation
- Disorientation (atropine)
- Sedation
- Amnesia (hyoscine)
Which famous plant causes atrophine poisoning?
Deadly nightshade
Why dont we use drugs for nACh receptors?
We wouldn’t be able to selectively activate SNS/PNS = mix of effects and would trigger autonomic reflexes
