title: Threshold properties of single motor units in superior head of human lateral pterygoid muscle.
abstract: The superior head of the human lateral pterygoid muscle (SHLP) may play a similar role in jaw movement as the inferior head (IHLP).
  
  
  OBJECTIVE
  The aim was to determine whether threshold properties of single motor units (SMUs) within SHLP during jaw tasks were comparable to those identified for IHLP.
  
  
  METHODS
  In 24 human subjects, SMUs were recorded intramuscularly from computer-tomography verified sites within SHLP during standardised jaw tasks recorded by a jaw-tracking device.
  
  
  RESULTS
  Of the 69 SMUs discriminated, 54 were active during contralateral, 52 during protrusive and 8 during ipsilateral jaw movements. The thresholds, at which SMUs commenced firing, decreased (p<0.05) as speed of contralateral or protrusive tasks increased. The data suggest an important role for SHLP in generation and control of contralateral and protrusive jaw movements. A number of lines of evidence were consistent with functional heterogeneity within SHLP.
  
  
  CONCLUSIONS
  The similarities in SHLP and IHLP functional properties support the proposal that both heads should be regarded as a system of fibers acting as one muscle.
authors.affiliation: Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW, Australia.
authors.forename: Manish Kumar
authors.initials: MK
authors.lastname: Bhutada
authors.forename: Intira
authors.initials: I
authors.lastname: Phanachet
authors.forename: Terry
authors.initials: T
authors.lastname: Whittle
authors.forename: Kamal
authors.initials: K
authors.lastname: Wanigaratne
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Peck
authors.forename: Greg M
authors.initials: GM
authors.lastname: Murray
mesh_terms: D000200:Action Potentials / Q000502:physiology; D004056:Differential Threshold / Q000502:physiology; D004567:Electrodes, Implanted; D004576:Electromyography / Q000295:instrumentation; D019054:Evoked Potentials, Motor / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008334:Mandible / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D009068:Movement; D009119:Muscle Contraction / Q000502:physiology; D011626:Pterygoid Muscles / Q000294:innervation*; D016059:Range of Motion, Articular / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology; D014057:Tomography, X-Ray Computed