Gamma motor neurons regulate the sensitivity of muscle spindle stretch receptors during active muscle contraction. Which functional consequence results from gamma motor neuron activation concurrent with alpha motor neuron discharge (alpha-gamma coactivation)?

• A Spindle intrafusal fiber shortening removes tension from the annulospiral endings, causing spindle silence during movement
• B Dynamic gamma neurons increase spindle sensitivity to the rate of length change during rapid contractions only
• C Spindle intrafusal fiber shortening prevents spindle unloading during muscle contraction, maintaining stretch receptor sensitivity ✓
• D Gamma activation inhibits Golgi tendon organs to prevent inhibition of the contracting muscle

Explanation

During voluntary contraction, alpha and gamma motor neurons are co-activated. The gamma motor neurons cause intrafusal fiber shortening of the muscle spindle, which takes up slack in the central sensory region around the annulospiral (Ia) endings. This prevents the spindle from becoming slack (unloaded) as the extrafusal muscle shortens, maintaining Ia afferent discharge. Preserving spindle sensitivity during movement allows the nervous system to detect any unexpected perturbation or load change during the contraction and mount a corrective stretch reflex.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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