Renshaw cells in the spinal cord provide recurrent inhibition of alpha motor neurons. They are activated by collaterals from the same alpha motor neuron axon and release which inhibitory neurotransmitter, and this circuit serves which functional purpose?

• A GABA; prevents spread of motor signals to adjacent spinal segments
• B Glycine; limits the frequency and intensity of motor neuron firing to prevent muscle fatigue ✓
• C Glycine; provides lateral inhibition to suppress antagonist motor neurons and sharpen motor output
• D GABA; inhibits Ia inhibitory interneurons to enable reciprocal inhibition

Explanation

Renshaw cells are glycinergic inhibitory interneurons that receive excitatory collaterals from alpha motor neurons and project back to inhibit the same (and nearby) motor neurons. By forming a negative feedback loop, they dampen motor neuron firing rate, preventing excessive or prolonged discharge that could cause tetanic contractions and metabolic fatigue. Renshaw cell inhibition is blocked by strychnine (glycine receptor blocker) and tetanus toxin (prevents glycine release), explaining the spastic tetany seen in tetanus and strychnine poisoning. Lateral inhibition and reciprocal inhibition are mediated by separate Ia inhibitory interneurons.

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

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Written and medically reviewed by the StethoPrep medical team.