Sensory ‘Cross-Terminals’ Between Dymamic and Static Intrafusal Fibers in Rat Muscle Spindles

  • Jon M. Walro
  • Jan Kucera


Separate motor pathways for controlling dynamic (velocity of muscle stretch) and static (length of muscle) sensitivity are present in muscle spindles of the cat (Boyd et al., 1977). The pattern of afferent innervation parallels this separation of motor pathways in cat spindles. Each muscle spindle in the cat receives only one primary afferent which terminates on all three major types of intrafusal fiber (Banks et al., 1982). However, the input of the dynamic bag fiber is separated from that of the static bag and chain fibers by pacemakers located at terminal heminodes of branches of the primary afferent which terminate on the bag1 fiber and at corresponding sites of branches which terminate on the bag2 and chain fibers (Quick et al., 1980; Banks et al., 1982). Presumably the two different responses observed from primary spindle afferents result from differential excitation of pacemakers related to differences in the viscoelastic properties of intrafusal fibers.


Extensor Digitorum Longus Muscle Spindle Primary Afferent Motor Axon Extensor Digitorum Longus Muscle 
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Copyright information

© Springer Science+Business Media New York 1988

Authors and Affiliations

  • Jon M. Walro
    • 1
    • 2
  • Jan Kucera
    • 1
    • 2
  1. 1.Department of AnatomyNortheastern Ohio Universities, College of MedicineRootstownUSA
  2. 2.Department of NeurologyBoston UniversityBostonUSA

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