Relationships between spindle density, muscle architecture and fibre type composition in different parts of the...

The occurrence of muscle spindles was studied in the masseter muscle of rabbits by light-microscopy of whole muscle sections. The distribution of the spindles appeared to be heterogeneous. Most spindles lay in the anterior/deep and mid-parts of the masseter. The lateral/superficial part contained only a few muscle spindles. The distribution of the spindles is correlated to the distribution of slow twitch (type I) extrafusal fibres. This means that spindles, like type I fibres might be involved in the control of fine movements and posture. Spindle density and type I fibre density increase with distance from the temporomandibular joint. This could mean that spindles are involved in controlling bite force.