Presynaptic inhibition differs from postsynaptic (Renshaw-type) inhibition chiefly because it:

• A Hyperpolarizes the alpha motor neuron soma via GABA-A receptors
• B Involves collateral activation of an inhibitory interneuron driven by the same motor neuron
• C Uses glycine released from an interneuron acting on the target neuron dendrites
• D Acts on an axo-axonic synapse to reduce calcium entry into the incoming afferent terminal, decreasing transmitter release ✓

Explanation

Presynaptic inhibition is produced by GABAergic axo-axonic interneurons synapsing on the terminal of a primary afferent. GABA acts mainly on GABA-D receptors, increasing potassium conductance and closing presynaptic calcium channels, so less transmitter is released while the postsynaptic cell's own excitability is unchanged. The distractor A describes classic postsynaptic IPSP generation, and B describes recurrent inhibition, the circuit already tested elsewhere.

Reference: Ganong's Review of Medical Physiology, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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