Evidence for γs Innervation of Long Chain Fibres

Nuclear chain fibres are classically regarded as being much shorter and thinner than bag fibres, either bag1 or bag2. However, Barker et al. (1976) noticed that some spindles possessed one or more chain fibres with unusually long poles, often of similar length to the bag fibres. As an estimate of the incidence of these ‘long chain’ fibres they assessed the proportion of spindles containing at least one chain fibre pole that extended for more than 1mm beyond the end of the capsule. Kucera (1980) formalised this practical criterion as a definition of a class of long chain fibres each of which possessed at least one long pole. Since that time, long chain fibres have often been treated as though they formed a distinct type of intrafusal fibre with a specific static beta (βs) innervation (Kucera, 1982, 1984; Barker & Banks, 1986). Here we give evidence in detail of both static β and static γ innervation of long chain fibres.