The Renshaw cell in the spinal cord provides recurrent inhibition to motor neurons. Which of the following accurately describes this circuit?

• A Alpha motor neuron axon collaterals activate glycinergic Renshaw cells, which inhibit the same and neighbouring alpha motor neurons, limiting excessive firing ✓
• B Renshaw cells are glutamatergic interneurons that provide positive feedback to enhance motor neuron output during sustained contractions
• C Renshaw cells receive input from the Ia afferents and provide disynaptic inhibition to antagonist motor neurons (reciprocal inhibition)
• D Renshaw cells are activated by Group Ib afferents from Golgi tendon organs to prevent muscle damage during overload

Explanation

Renshaw cells are inhibitory interneurons in the ventral horn of the spinal cord. They receive excitatory (cholinergic, via nicotinic receptors) input from collateral branches of alpha motor neuron axons. In turn, Renshaw cells release glycine onto the same alpha motor neurons (recurrent self-inhibition) and onto neighbouring alpha motor neurons, providing a negative feedback circuit that regulates the overall level of motor neuron pool excitability and prevents runaway firing. Renshaw cells also inhibit Ia inhibitory interneurons, thereby modulating reciprocal inhibition. Tetanus toxin and strychnine block Renshaw cell (glycinergic) inhibition, causing spastic paralysis. Option C describes Ia inhibitory interneurons (reciprocal inhibition), not Renshaw cells. Option D describes the inverse myotatic reflex via Golgi tendon organs and Ib afferents.

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

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