Functional Maturation of Muscle Spindles in the Tenuissimus Muscles of Kittens

Almost thirty years ago, Skoglund (1960) published the results of a series of experiments in which he was able to assess the acquisition of physiological function in maturing gastrocnemius muscle spindles of kittens from birth to 45 days of age. He found that all stretch receptors responded phasically in newborn and young kittens. It was not until 6–10 days after birth that muscle spindles began to develop tonic discharges in response to a stretch and hold stimulus. At 17 days of age, the effect of gamma motoneurons on spindle discharges was demonstrable and Skoglund presented evidence for an earlier alpha innervation of the spindles.