Neuromuscular Blockers Flashcards
Is it the presynaptic or postsynaptic nicotinic receptor that is pentameric?
Postsynaptic nicotinic receptor = a2,B1,d1,e1
In relation to muscle contraction what neurotransmitter does the presynaptic nicotinic receptor release?
Ach molecules
When the presynaptic nicotinic receptor releases Ach molecules what must they bind to in order to cause a muscle contraction? Explain how that muscle contraction takes place?
two Ach molecules must attach to the two alpha subunits on the motor end plate at the same time to allow the ion cannel to open, when it opens sodium and calcium enter the cell and potassium leaves the cell. The influx of electrolytes makes the inside of the cell relatively positive (previously negative at rest) and this allows an action potential to propagate and muscle contraction takes place.
Why does chloride not enter the nicotinic receptor?
chloride is repelled by the strong negative charges situated inside the channel
After a muscle contraction what allows the muscle to relax?
Acetylcholinesterase which is positioned around the pre- and postsynaptic nicotinic receptor. It hydrolyzes Ach almost immediately after it activates these receptors.
What would happen if acetylcholinesterase was not around?
The muscle would contract but then would not quickly relax, it would stay contracted longer, until the Ach dissociated from the receptor.
What are the two types of extra junctional receptors?
Where the epsilon subunit is replaced by the gamma subunit.
Where all five subunits are alpha subunits. (named alpha 7 even though it only has 5 alpha subunits)
What situations allow for the junctional receptors to be replaced by extrajunctional receptors?
Denervation later in life
prolonged immobility
What conditions would caution the use of Succinylcholine?
Upper or lower motor neuron injury
spinal cord injury
burns
skeletal muscle trauma
CVA
prolonged chemical denervation (magnesium, long term NMB infusion, clostridial toxin)
Tetanus
Sever sepsis
Muscular dystrophy
Musclular atrophy for any reason
In a person with normal nicotinic receptors, how much does Sch. increase the potassium and for how long?
0.5-1.0 mEq/L for up to 10-15 minutes
How do extra junctional receptors respond to succinylcholine?
much more sensitive to succinylcholine, they remain open for a longer period of time.
If the extra junctional receptors stay open longer in response to Sch. why does this matter?
When the receptor opens it allows potassium out of the cell, the longer the cell is open the more potassium can leak out thus more increase in serum potassium levels. This can cause life threatening hyperkalemia
what are the two extra junctional receptors depolarized by?
a2B1d1y1 is depolarized by succinylcholine
a7 is depolarized by Sch. and choline the metabolite of Sch.
As a general rule how long should you avoid Sch. after a denervation injury?
avoid 24-48 hours following the injury and for at least one year after
What is special for burns and the use of Sch. how long do you avoid it’s use?
the risk of hyperkalemia may persist for several years after the burn (especially if the patient has contractures)
