NMBD's Flashcards
True or False: Nicotinic receptors are located only on the post-synaptic end-plate.
False, located both pre and post synaptic.
Where are acetylcholinesterase molecules found?
Around post synaptic nicotinic receptors and in the synaptic cleft
Acetylcholine is synthesized from _____ and ____ through the action of _____
AcetylCoA and Choline, Choline Acetyltransferase (ChAT)
Release of Ach depends on the entry of ____ in to the terminal
Calcium
What does Calcium do once inside the nerve terminal?
causes vesicles to fuse with nerve cell membrane and exocytosis of Ach
What happens when Ach binds to a pre-synaptic nicotinic Ach receptor?
A positive feedback loop-it increases synthesis and release of Ach.
____ number of molecules of Ach must combine with 2 ____ subunits on the nicotinic receptor.
2, alpha
When both nicotinic subunits are occupied by Ach, the channels snap open and __ and ____ flow into the cell and ____ flows out.
Na and Ca flow into, K flows out
Acetylcholinesterase splits Ach into ___ and ____
acetate and choline
____ is transported back to the pre-synaptic terminal where it’s reconverted to Ach. ____ diffuses away.
Choline, acetate
What are extrajunctional nicotinic receptors?
Proliferate in response to paralysis, dystrophies, upper/lower motor neuron injury, major burns.
What happens as a result of extrajunctional nicotinic receptors?
Channels stay open 4x longer and upregulate-causes hyperkalemia
What are the subunits of a nicotinic receptor?
2 alpha, 1 beta, 1 delta, 1 epsilon
Depolarizing muscle relaxants act as acetylcholine receptor ______
Agonists
Non-depolarizing muscle relaxants act as ____ ____
competitive antagonists
Which medication is a depolarizing muscle relaxant?
Succinylcholine
Which medication is a long acting non-depolarizing muscle relaxant?
Pancuronium
Which medications are intermediate acting non-depolarizing muscle relaxants? (4)
Atracurium, Cisatracurium, rocuronium, vecuronium
Which medication is a short acting non-depolarizing muscle relaxant?
Mivacurium
What is the mechanism of action for Succinylcholine?
It mimics Ach. It works on the pre-synaptic receptors to mobilize ach and works at post synaptic receptors to open channels-Na/Ca enters the cell, K leaves the cell. This creates a prolonged depolarization.
What is the absolute refractory period?
action potentials cannot be initiated in the skeletal muscle until it REpolarizes. Voltage gated sodium channels in the membrane adjacent to the post synaptic terminal (motor end plate) snap in to the inactivated state.
What is the following for Succinylcholine? Dose: Onset: Duration: What is it broken down by?
0.5-1mg/kg
30sec
3-5 min
Plasma Cholinesterase (aka pseudocholinesterase or butyrocholinesterase)
What is the metabolite of succinylcholine?
Succinylmonocholine
What percent of succinylcholine actually reaches the neuromuscular junction? or What percent isn’t metabolized?
10%
What is the name of the enzyme that breaks down succinylcholine?
Pseudocholinesterase (aka plasma cholinesterase, butyrocholinesterase)
What are some example of situations that will have a prolonged blockage by succinylcholine?
Atypical plasma cholinesterase, severe liver disease, use of anticholinesterase medications
What are some drugs that lower plasma cholinesterase, which would prolong the effect of succinylcholine?
Metaclopramide Esmolol Neostigmine & Pyridostigmine Echothiophate Oral contraceptives/estrogen Cyclophosphamide MAOI's N2 Mustard
What are some conditions that lower plasma cholinesterase?
Atypical Anticholinesterase Severe Liver disease Chronic kidney disease burns advanced age Organophosphate poisoning neoplasm malnutrition late pregnancy
What does a dibucaine number tell you?
reflects the percentage of plasma cholinesterase that is inhibited when dibucaine is given. It has NO effect on atypical plasma cholinesterase.
Does a dibucaine number tell you the quantity or quality of the plasma cholinesterase enzyme?
Quality
About how long does it take to recover is your dibucaine number is above 80? 40-60? 20 and below?
above 80: 5-10 min. normal response
40-60: 20-30 min
20 and below: 4-8hr
What is a way to minimize fasciculations that may cause myalgias?
Give 1/10 of the ED 95 dose of a non-depolarizing muscle relaxant. (Ex. Roc, vec.) 3-5 min before giving succinylcholine
What are side effects of succinylcholine?
Bradycardia Tachycardia Hypertension Hyperkalemia Myalgias Myo-globinuria Increased intra gastric pressure Increased intracranial pressure Increased intraocular pressure Malignant Hyperthermia Masseter Spasm Prolonged respiratory paralysis (with atypical plasma cholinesterase)
Which receptors are being stimulated if succinylcholine causes bradycardia?
Muscarinic receptors
Which receptors are being stimulated in succinylcholine causes tachycardia and hypertension?
Autonomic ganglia nicotinic receptors
What are factor that prolong the depolarizing block of succinylcholine?
Antibiotics (especially aminoglycosides) local anesthetics Anticholinesterase agents (increases Ach Hyperkalemia Hypermagnesemia Inherited pseudo-cholinesterase effect Lithium
What are potential conditions that accentuate succinylcholine -induced hyperkalemia?
Undiagnosed muscular dystrophy burn (7-10 days post acute burn) Severe abdominal infections Severe metabolic acidosis Conditions with up-regulation of extra-junctional acetylcholine receptors (para/hemipalegia, muscular dystophies, gullain-barre, upper motor neuron lesions/injuries, CVA, etc)
What are the subunits on an extra-junctional nicotinic receptor?
7 alpha subunits and a gamma subunit (instead of an epsilon)