The Renshaw cell in the spinal cord provides which type of inhibition to alpha motor neurons, and what is its functional significance?

• A Feed-forward inhibition from Ia afferents; coordinates agonist-antagonist muscle pairs during movement
• B Presynaptic inhibition from descending tracts; suppresses spinal reflexes during voluntary movement
• C Disinhibition via GABA-B receptors; releases motor neuron output from tonic inhibition during locomotion
• D Recurrent inhibition via glycinergic interneurons; limits excessive motor neuron discharge and stabilises firing frequency ✓

Explanation

Renshaw cells are inhibitory spinal interneurons activated by recurrent collaterals of alpha motor neuron axons. They release glycine back onto the same and neighbouring alpha motor neurons (and Ia inhibitory interneurons), creating a negative feedback loop. This recurrent inhibition stabilises motor neuron firing rate and prevents runaway excitation ('clonus' suppression). In strychnine poisoning, glycine receptor blockade eliminates Renshaw cell inhibition, producing violent tetanic spasms. Ia inhibitory interneurons (feed-forward inhibition) mediate reciprocal inhibition during the stretch reflex.

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

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