Pharmacology of the NMJ - Medicine BM5 NLM1

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What is flaccid paralysis?
Prolonged stimulation due to the presence of depolarising drugs (anti-cholinesterases)
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Which two substances combine to form ACh in the presynaptic terminal?
Acetyl CoA & Choline
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Which two substances are formed when AChE breaks down ACh?
Acetic Acid & Choline
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To what type of receptors does ACh bind at the NMJ?
Nicotinic Type II
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What is a Mini End Plate Potential (MEPP)?
A small depolarization that does not reach the threshold value, caused by ACh fusing without an axonal signal
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Does a Mini End Plate Potential (MEPP) cause a muscle twitch?
No
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Complete the sentence: Whole muscle contraction is...
...a summation of the muscle fibre twitches
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Complete the following sentence: Maintaining whole muscle contraction requires...
...a series of asynchronous muscle fibre twitches
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What is the mechanism of action of a large number of local anaesthetics?
They block the sodium channels involved in propagating the nerve impulse
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In which fish is tetrodotoxin commonly found?
Pufferfish
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How does tetrodotoxin act?
It systemically blocks the sodium channels involved in propagating the nerve impulse
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How does Botulinum toxin work?
It blocks the release of ACh
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Although Botulinum toxin is used cosmetically, what disease is it also used to help manage symptoms?
Cerebral Palsy
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What type of drug is Vecuronium in relation to its inhibition of end plate depolarization?
Competitive Antagonists
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With regards to Vecuronium, complete the equation: Degree of Blockade =
Concentration of Vecuronium/Concentration of ACh
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What percentage of ACh receptors need to be blocked in order to create a transmission block?
80%
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What is Vecuronium commonly used for?
Muscle relaxation (anaesthesia)
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If Vecuronium is given to a patient with Myasthenia Gravis, what will happen to the transmission block comparative to a person without MG on Vecuronium
Enhanced
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Select the most correct statement about suxamethonium.
It is chemically related to ACh but is not metabolised by AChE
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Suxamtheonium stimulates Nicotinic Type II receptors at the NMJ and causes muscle contraction. What happens after this?
The muscle fibre will relax but the end plate remains depolarized (causing flaccid paralysis)
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What action does suxamethonium cause?
Depolarizing blockade
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If Suxamethonium is given to a patient with Myasthenia Gravis, what will be the effect on the depolarizing block?
Reduced
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What is the speed of onset of Vecuronium?
2-4mins
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What is the speed of onset of Suxamethonium?
1-2mins
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True or false: Vecuronium's onset is uneventful, whereas Suxamethonium's onsent causes fasciculations?
True
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What is the duration of action of Vecuronium?
30-40mins
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What is the duration of action of Suxamethonium?
~5mins
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Both Vecuronium and Suxamethonium are metabolised, but they differ in their method of clearance. How is Vecuronium cleared?
Liver metabolism & voided in urine
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Both Vecuronium and Suxamethonium are metabolised, but they differ in their method of clearance. How is Suxamethonium cleared?
Plasma Cholinesterase
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What are the possible post-operative effects of Suxamethonium?
Muscle pain
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Metabolism of ACh in the synaptic cleft is rapid. Approximately what speed does it take place at?
5x10^6 molecules per msec
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Edrophonium is a short acting anticholinesterase. What is the duration of action of Edrophonium?
2-5min
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Edrophonium is a short actin anticholinesterase. What is it used to diagnose?
Myasthenia Gravis
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Neostigmine is a medium acting anticholinesterase. What is the duration of action of neostigmine?
6-8hrs
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True or false: Neostigmine is a quaternary ammonium so does not cross the blood-brain barrier, whereas Physostigmine is a tertiary ammonium so will cross the blood-brain barrier?
True
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Neostigmine is a medium-acting anticholinesterase. What is it used to treat?
Myasthenia Gravis
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Physostigmine is a medium-acting anticholinesterase. What is it used to treat?
Glaucoma
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Select the correct example of an organophosphate.
Malathion
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True or false: Organophosphates will not cross the blood-brain barrier?
False
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If you suspect organophosphate poisoning, which drug should be given ASAP (within 10 mins)?
Pralidoxime
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Identify the symptom most commonly assoicated with organophosphate poisoning.
Respiratory muscle paralysis
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On which nervous system do organophosphates act?
Parasympathetic
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How do organophosphates cause respiratory paralysis?
Bind irreversibly to AChE, preventing breakdown of ACh at NMJ
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What emergency procedure is carried out on someone with organophosphate poisoning
Artificial respiration
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Other cards in this set

Card 2

Front

Which two substances combine to form ACh in the presynaptic terminal?

Back

Acetyl CoA & Choline

Card 3

Front

Which two substances are formed when AChE breaks down ACh?

Back

Preview of the front of card 3

Card 4

Front

To what type of receptors does ACh bind at the NMJ?

Back

Preview of the front of card 4

Card 5

Front

What is a Mini End Plate Potential (MEPP)?

Back

Preview of the front of card 5
View more cards

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