Long-term potentiation (LTP) in hippocampal CA1 neurons requires NMDA receptor activation. The NMDA receptor is considered a 'coincidence detector' because it requires which two simultaneous events for Ca²⁺ entry?

• A Glutamate binding to the NMDA receptor AND sufficient postsynaptic depolarization to relieve the Mg²⁺ block of the channel pore ✓
• B Presynaptic GABA release AND postsynaptic AMPA receptor activation
• C Simultaneous activation of mGluR1 and mGluR5 metabotropic glutamate receptors
• D Nitric oxide synthesis in the postsynaptic cell AND retrograde endocannabinoid signaling

Explanation

At resting membrane potential, the NMDA receptor channel pore is blocked by Mg²⁺ even when glutamate and glycine (co-agonist) are bound. Depolarization of the postsynaptic membrane (often by prior AMPA receptor activation) relieves the voltage-dependent Mg²⁺ block, allowing Ca²⁺ influx. Thus the NMDA receptor requires both a chemical signal (glutamate binding) and an electrical signal (postsynaptic depolarization) — acting as a molecular coincidence detector for Hebbian plasticity. The resultant Ca²⁺ rise activates CaMKII, leading to AMPA receptor phosphorylation and LTP.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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