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19 Cards in this Set
- Front
- Back
what are the 2 types of NML blockers?
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nondepolarizing = antagonistic competitive
depolarizing = agonist |
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what is the mechanism for nondepolarizing NMJ blockers?
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competition with Ach
prevent depolarization of receptor |
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what is the structure of the post-synaptic nicotinic receptor?
subunits? domains? |
5 subunits
α2βδγ each subunit has 4 domains 2 binding pockets δα & αβ |
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role of Ach receptor on pre-synaptic motor axon terminal?
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moves vesicles to synaptic membrane for release
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compare kidney vs liver excretion of non-de-polarizing NM blockers
1/2 life duration of action |
kidney >> 1/2 life, duration of action
liver << 1/2 life, duration of action metabolites can accumulate |
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how are NM blocking drugs administered and why?
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give parenterally bc inactive orally
highly polar compounds with poor lipid solubility due to quaternary N don't cross membranes so stay in plasma --> vol of distribution about = blood vol |
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for nondepolarizing NM blockers
what is the relationship between potency, onset and duration of action |
least potent have fastest onset and shortest duration of action
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what is the relationship between end plate potential (epp) and Ach released?
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magnitude of epp is directly related to amount of Ach released
if small, impulse not generated if large, more Ach released and adjacent muscle membrane depolarizes --> action potential propagated along entire fibre |
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what is the structure of succinylcholine?
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2 Ach molecules linked end to end
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what is the duration of succinylcholine and why?
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short duration of action due to rapid hydrolysis by cholinesterase in the plasma
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mechanism of action of nondepolarizing NM receptor blocker?
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binds to the receptor at the same site as Ach and blocks Ach from binding --> prevents opening of the channel
competitive with Ach antagonistic |
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what is the only clinically useful depolarizing blocking drug?
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succinylcholine
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what reverses residual blockade by nondepolarizing NM blockers/muscle relaxants?
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cholinesterase inhibitors reverse residual blockade
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how do depolarizing blockers work?
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occupy the receptor --> the motor end plate --> contraction
then blocks the channel --> desensitize the end plate by causing persistent depolarization --> flaccid paralysis |
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how to cholinesterase inhibitors reverse depolarizing blockers?
phase I vs. phase II |
phase I = augmentation of phase I depolarizing blockade by cholinesterase inhibitors
phase II - reversal of blockade by cholinesterase inhibitors during phase II depolarizing blockade |
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what is phase I of depolarizing blockade?
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reacts with the nicotinic receptor to open the channel --> depolarization --> initial twitch --> remains depolarized bc succ not metabolized at the synapse --> flaccid paralysis
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what is phase II of depolarizing blockade?
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desensitization
channels act as if closed --> like nondepolarizing block |
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side effects of succinylcholine?
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- Bradycardia (muscarinic agonist reaction)
- Hyperkalemia - heart rate perturbations. - Increase intraocular pressure (nicotinic effect on extraocular muscles) - Post operative muscle pain |
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what happens with continued administration of succinylcholine?
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Continued administration brings to block (phase II), desensitization of the receptors and delay of recovery
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