The structural and functional development of muscle spindles and their connections in fetal sheep

Abstract

In this paper we have studied the structural and functional development of hindlimb muscle receptors and the connections of their afferent fibres in fetal sheep (n = 26) from 67-143 days of gestation (term = 146 days). By recording extracellular discharges in dorsal root ganglia (L7, S1) we have shown that muscle spindle afferents first respond to a ramp-and-hold stretch at mid-gestation (∼ 75 days). Silver-stained preparations of muscle spindles revealed that afferent fibres are just beginning to form annulospiral windings at this age. It therefore appears that the annulospiral formation is not a necessary requirement for the generation of the response. By 87-92 days some receptors had deve..