The sensitivity of this stretch receptor is adjusted by gamma motor neurons which innervate these contractile fibers. When the muscle is stretched, the intrafusal fibers detect this stretch. When the muscle contracts the gamma motor neuron fires and increases the tension on the intrafusal fibers. In this way the sensitivity of the muscle spindles resets to maintain its sensitivity to a change in the muscle length.
Molecular and Cellular Therapies for Motor Neuron Diseases (Hardcover)
The motor neuron diseases are a collection of progressive neurological disorders that finish motor neurons, the cells that resistor essential voluntary muscle movement such as speaking, walking, breathing etc.