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NBME 21 Answers
During an experiment, an investigator observes that ...
NMDA receptors are blocked by Mg2+ at the resting membrane potential
Amazing video dude. Somehow never learned this in neuro lol.
I forgot/didn't know this factoid and narrowed it to the correct answer and a wrong answer. Guess which one I chose?
>That means something was delaying NMDA receptor activating and the only answer that made sense as the Mg inhibiting NMDA at resting potential.
What makes the fasting gating kinetics choice incorrect then?
NMDA receptors are both voltage gated and ligand gated channels. Glutamate and aspartate are endogenous ligands for this receptor. Binding of one of the ligands is required to open the channel thus it exhibits characteristics of a ligand channel. If Em (membrane potential) is more negative than -70 mV, binding of the ligand does NOT open the channel (Mg2+ block on the NMDA receptor). IF Em is less negative than -70 mV binding of the ligand opens the channel (even though no Mg2+ block at this Em, channel will not open without ligand binding.
Out of the answer choices only NMDA receptors blocked by Mg2+ makes sense.
Hope this helps.