Figure 3.

Representative cross-sections taken at intervals throughout three sample spindles from a BEL soleus muscle to show the identification of intrafusal-fibre types, and to illustrate: (left column) the most common complement of one bag₂, one bag₁ and two chain fibres; (middle column) a spindle with two bag₂, one bag₁ and one chain fibre; and (right column) one of the largest spindles found in any strain with a complement of two bag₂, two bag₁ and four chain fibres. The box at the lower left of each micrograph gives the reference for the section in the format: slide number.section number. The box at the upper right gives the nominal distance from the first section in μm. In the spindle shown in the right column, the two bag₂ fibres are thought to have branched somewhere between sections 7.1 and 7.3, resulting in the appearance of four profiles in 7.3. Acid-stable ATPase following pre-incubation at pH 4.47; differential staining properties of the three types of intrafusal fibre are described in the text.