Can neck muscle spindle afferents activate fusimotor neurons of the lower limb?

Muscle Nerve. 2012 Mar;45(3):376-84. doi: 10.1002/mus.22300.

Abstract

Introduction: We investigated whether vibratory stimulation of the dorsal neck muscles activates fusimotor neurons of lower limb muscles in relaxed human subjects.

Methods: The triceps surae (TS) muscles of seated subjects (n = 15) were conditioned to leave their muscle spindles in either an insensitive (hold-long) or sensitive (hold-short) state. A vibrator (80 HZ) was applied to the dorsal neck muscles for 10 seconds. The tendon jerk was evoked from the right TS immediately before (during) or 5 seconds after (interposed) the offset of vibration.

Results: The size of the reflex after hold-long muscle conditioning and after neck vibration was significantly smaller than the control hold-short reflex (P < 0.001). However, after hold-short conditioning, neck vibration significantly increased tendon jerk amplitude, both during (P = 0.001) and interposed (P = 0.026).

Conclusion: Dorsal neck vibration increases spinal reflex excitability of the TS in relaxed and seated subjects, but not through fusimotor excitation.

MeSH terms

  • Adult
  • Afferent Pathways / physiology*
  • Analysis of Variance
  • Electromyography
  • Forearm / innervation
  • Humans
  • Lower Extremity / anatomy & histology*
  • Lower Extremity / physiology
  • Male
  • Motor Neurons, Gamma / physiology*
  • Muscle Spindles / physiology*
  • Neck Muscles / anatomy & histology*
  • Neck Muscles / innervation
  • Physical Stimulation
  • Quadriceps Muscle / cytology*
  • Reflex, Stretch / physiology
  • Time Factors
  • Vibration
  • Young Adult