NMJ Flashcards
T/F?
The nicotinic receptors at skeletal muscle and autonomic ganglia are identical
F
ganglia= N1, skeletal muscle=N2
T/F?
Suxamethonium is a competitive antagonist of N2 receptors
F
Agonist
Persistent depolarisation (flaccid paralysis)
T/F?
Botulinum toxin is used to treat excessive sweating
T
If locally injected, sympathetic innervation, muscarinic receptors that use ACh
How does Lidocaine work?
Blocks voltage gated Na+ channels at NMJ so no EPP
= local anaesthetic
Name a drug that works in the same way as Lidocaine
Tetrodotoxin
How does Botulinum toxin work? What is it used to treat?
Inhibits release of ACh from presynaptic vesicles
Treats muscle spasm in cerebral palsy, also used cosmetically and locally for excess sweating
How does Vecuronium work?
Competitive antagonist of N2 receptors to prevent contraction of skeletal muscle (transmission block)
Needs >80% receptors blocked to work
How do you reverse the effects of vecuronium?
Neostigmine is a ACh esterase inhibitor so increases conc of ACh in cleft and reverses affects of vecuronium antagonism
How does suxamethonium work?
Causes contraction of skeletal muscle but is not degraded quickly, so end plate remains depolarised after muscle has contracted= flaccid paralysis
Also called depolarising block
What does Neostigmine do to suxamethonium?
Nothing, suxamethonium is degraded by plasma choline esterase not AChE
How do Suxamethonium’s actions differ in myasthenia gravis?
In MG there are less N2 receptors so less places for suxamethonium to bind so depolarising block is reduced
How do Vecuronium’s actions differ in myasthenia gravis?
Less N2 receptors so easier to block >80% of them so less Vecuronium needed for transmission block
Which NMJ muscle relaxant has quickest onset?
Suxamethonium (1-2 mins instead of 2-4 mins)
Which NMJ muscle relaxant has longest duration of action?
Vecuronium (30-40mins instead of 5 mins)
How are the 2 NMJ muscle relaxants cleared?
Vecuronium by liver metabolism, Suxamethonium by plasma choline esterase
SE of Suxamethonium?
Muscle pain after operation as all muscles have to contract first before the depolarising block works
Name an irreversible anticholineesterase
Organophosphates (Malathion, Sarin Gas) such as pesticides or nerve gases
Causes neuromuscular blockade and overactivity of PNS
How do you treat organophosphate poisoning?
With Pralidoxime (quickly!)
Cleaves AChE-organophosphate complex
Artificial respiration and Atropine to reverse effects on PNS
Takes up to a month till effects die down as you have to wait for body to make new AChE
Which muscle relaxant would you use for someone who is undergoing ECT?
Suxamehtonium, short duration of action and terminated by metabolism. No need for ventilation
Which muscle relaxant would you use for GI surgery?
Vecuronium- longer duration of action, no after effects, effects can be reversed by neostigmine at end of operation.
What does Neostigmine do?
Inhibits AChE so more ACh in cleft
Reverses effects of transmission block from vecuronium
Also stimulates PNS and sweat glands
T/F?
The rate of metabolism of Suxamethonium can be genetically determined
T- you need plasma cholinesterase to break it down and some people lack it
T/F?
Suxamthonium is 3 ACh molecules chemically joined
F- It is 2 AChs joined
How do you know if a drug is related to Vecuronium?
Has CURARE in is or CUR
What is edrophonum?
Short acting AChE inhibitor
Name a drug similar to neostigmine?
Physostigmine (only difference is it can cross blood-brain barrier)
