NMJ

Question 1

T/F?

The nicotinic receptors at skeletal muscle and autonomic ganglia are identical

Answer 1

F

ganglia= N1, skeletal muscle=N2

Question 2

T/F?

Suxamethonium is a competitive antagonist of N2 receptors

Answer 2

F
Agonist
Persistent depolarisation (flaccid paralysis)

Question 3

T/F?

Botulinum toxin is used to treat excessive sweating

Answer 3

T

If locally injected, sympathetic innervation, muscarinic receptors that use ACh

Question 4

How does Lidocaine work?

Answer 4

Blocks voltage gated Na+ channels at NMJ so no EPP

= local anaesthetic

Question 5

Name a drug that works in the same way as Lidocaine

Answer 5

Tetrodotoxin

Question 6

How does Botulinum toxin work? What is it used to treat?

Answer 6

Inhibits release of ACh from presynaptic vesicles

Treats muscle spasm in cerebral palsy, also used cosmetically and locally for excess sweating

Question 7

How does Vecuronium work?

Answer 7

Competitive antagonist of N2 receptors to prevent contraction of skeletal muscle (transmission block)
Needs >80% receptors blocked to work

Question 8

How do you reverse the effects of vecuronium?

Answer 8

Neostigmine is a ACh esterase inhibitor so increases conc of ACh in cleft and reverses affects of vecuronium antagonism

Question 9

How does suxamethonium work?

Answer 9

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

Question 10

What does Neostigmine do to suxamethonium?

Answer 10

Nothing, suxamethonium is degraded by plasma choline esterase not AChE

Question 11

How do Suxamethonium’s actions differ in myasthenia gravis?

Answer 11

In MG there are less N2 receptors so less places for suxamethonium to bind so depolarising block is reduced

Question 12

How do Vecuronium’s actions differ in myasthenia gravis?

Answer 12

Less N2 receptors so easier to block >80% of them so less Vecuronium needed for transmission block

Question 13

Which NMJ muscle relaxant has quickest onset?

Answer 13

Suxamethonium (1-2 mins instead of 2-4 mins)

Question 14

Which NMJ muscle relaxant has longest duration of action?

Answer 14

Vecuronium (30-40mins instead of 5 mins)

Question 15

How are the 2 NMJ muscle relaxants cleared?

Answer 15

Vecuronium by liver metabolism, Suxamethonium by plasma choline esterase

Question 16

SE of Suxamethonium?

Answer 16

Muscle pain after operation as all muscles have to contract first before the depolarising block works

Question 17

Name an irreversible anticholineesterase

Answer 17

Organophosphates (Malathion, Sarin Gas) such as pesticides or nerve gases
Causes neuromuscular blockade and overactivity of PNS

Question 18

How do you treat organophosphate poisoning?

Answer 18

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

Question 19

Which muscle relaxant would you use for someone who is undergoing ECT?

Answer 19

Suxamehtonium, short duration of action and terminated by metabolism. No need for ventilation

Question 20

Which muscle relaxant would you use for GI surgery?

Answer 20

Vecuronium- longer duration of action, no after effects, effects can be reversed by neostigmine at end of operation.

Question 21

What does Neostigmine do?

Answer 21

Inhibits AChE so more ACh in cleft
Reverses effects of transmission block from vecuronium
Also stimulates PNS and sweat glands

Question 22

T/F?

The rate of metabolism of Suxamethonium can be genetically determined

Answer 22

T- you need plasma cholinesterase to break it down and some people lack it

Question 23

T/F?

Suxamthonium is 3 ACh molecules chemically joined

Answer 23

F- It is 2 AChs joined

Question 24

How do you know if a drug is related to Vecuronium?

Answer 24

Has CURARE in is or CUR

Question 25

What is edrophonum?

Answer 25

Short acting AChE inhibitor

Question 26

Name a drug similar to neostigmine?

Answer 26

Physostigmine (only difference is it can cross blood-brain barrier)