Long-term potentiation (LTP) in the hippocampus is the cellular basis for learning and memory. The NMDA receptor acts as a 'coincidence detector.' This means:

• A NMDA receptors require simultaneous ligand binding (glutamate) AND relief of Mg²⁺ block (by sufficient depolarization) to open and allow Ca²⁺ entry, requiring both pre- and postsynaptic activity simultaneously ✓
• B NMDA receptors coincidentally activate both AMPA and kainate receptors when glutamate binds
• C NMDA receptors detect temporal coincidence between two different glutamate inputs from separate presynaptic neurons
• D The Ca²⁺ influx via NMDA receptors coincidentally activates both protein kinase A and protein kinase C simultaneously

Explanation

NMDA receptors are ionotropic glutamate receptors blocked at resting membrane potential by Mg²⁺ in the channel pore. For NMDA receptor activation and Ca²⁺ influx, TWO conditions must be met simultaneously: (1) glutamate must bind (presynaptic activity) AND (2) the postsynaptic membrane must be sufficiently depolarized (through concurrent AMPA receptor activation) to expel the Mg²⁺ block. This dual requirement — presynaptic neurotransmitter release AND postsynaptic depolarization — makes NMDA receptors molecular coincidence detectors implementing Hebbian learning. Ca²⁺ influx then activates CaMKII, which phosphorylates AMPA receptors and inserts new ones into the synapse, strengthening the connection (LTP).

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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