What's what
Nerve action potentialThe impulse traveling down the axon. Each stimulus sends one (DBS sends a burst of 3).
ACh vesiclePacket of ACh. The cluster at the top is the reserve pool, and the row on the bottom membrane is docked, ready to release.
Vesicle fusingA docked vesicle fusing with the membrane and dumping its ACh into the cleft.
ACh moleculesReleased into the cleft. They bind receptors, then get broken down.
Acetylcholinesterase (AChE)The pac-man. It chews up ACh in the cleft within milliseconds so the receptor resets. Greyed out = inhibited by neostigmine.
MobilizationVesicles moving from the reserve pool to the docking sites.
Presynaptic + feedbackACh on the presynaptic receptor speeds mobilization. A red X means the feedback is blocked, which is the cause of fade.
Nicotinic ACh receptorOn the nerve terminal edges = presynaptic α3β2. On the fold crests = postsynaptic (muscle type). Hollow = closed.
Open receptor channelAgonist bound, channel open, Na+ flowing in to depolarize the end plate.
RocuroniumPurple block sitting on a receptor. Competitive antagonist: ACh bounces off.
Succinylcholine (Phase I)Gold dot on an open receptor. The agonist holds the channel open, so the end plate stays depolarized.
Desensitized receptor (Phase II)Grey receptor with succinylcholine on it that no longer responds.
Perijunctional Na+ channelIn the depths of the junctional folds. Fires the muscle action potential. Turns yellow when it fires.
Inactivated Na+ channelRed with the inactivation gate (ball) closed. It cannot fire until the end plate repolarizes: the Phase I block.
SugammadexGold ring with rocuronium trapped inside (1:1 encapsulation).
Muscle action potentialYellow band spreading out from the end plate. The stripes (sarcomeres) squeeze together as the fiber contracts.
Twitch monitor (adductor pollicis)
100 muscle fibers
Each fiber has its own margin of safety. fired
below threshold
end plate stuck depolarized