Fast and slow intrafusal fibre type systems in chicken leg muscle spindles.

The results of this study indicate that in serial sections incubated with monoclonal antibodies against MHC and stained for mATPase, intrafusal fibres in chicken leg muscle spindles are separable into slow and fast types. As observed here, fast fibres are a homogeneous group; however, it had been shown earlier (Maier & Zak, 1990) that based on relative amounts of slow MHC, the slow fibres can be further divided into 2 subgroups. These 3 types of intrafusal fibre conform to 3 recently demonstrated patterns of motor innervation (Maier, 1991). It is suggested that the respective actions of slow and fast intrafusal fibres produce different components of the afferent discharge of chicken muscle spindles.