Phasic and tonic stretch reflexes in muscles with few muscle spindles: human jaw-opener muscles

Abstract We investigated phasic and tonic stretch reflexes in human jaw-opener muscles, which have few, if any, muscle spindles. Jaw-unloading reflexes were recorded for both opener and closer muscles. Surface electromyographic (EMG) activity was obtained from left and right digastric and superficial masseter muscles, and jaw orientation and torques were recorded. Unloading of jaw-opener muscles elicited a short-latency decrease in EMG activity (averaging 20 ms) followed by a short-duration silent period in these muscles and sometimes a short burst of activity in their antagonists. Similar behavior in response to unloading was observed for spindle-rich jaw-closer muscles, although the latency of the silent period was statistically shorter than that observed for jaw-opener muscles (averaging 13 ms). Control studies suggest that the jaw-opener reflex was not due to inputs from either cutaneous or periodontal mechanoreceptors. In the unloading response of the jaw openers, the tonic level of EMG activity observed after transition to the new jaw orientation was monotonically related to the residual torque and orientation. This is consistent with the idea that the tonic stretch reflex might mediate the change in muscle activation. In addition, the values of the static net joint torque and jaw orientation after the dynamic phase of unloading were related by a monotonic function resembling the invariant characteristic recorded in human limb joints. The torque-angle characteristics associated with different initial jaw orientations were similar in shape but spatially shifted, consistent with the idea that voluntary changes in jaw orientation might be associated with a change in a single parameter, which might be identified as the threshold of the tonic stretch reflex. It is suggested that functionally significant phasic and tonic stretch reflexes might not be mediated exclusively by muscle spindle afferents. Thus, the hypothesis that central modifications in the threshold of the tonic stretch reflex underlie the control of movement may be applied to the jaw system.

[1]  The unloading reflex in masticatory muscles of man. , 1968, Archives of oral biology.

[2]  P. G. Dellow,et al.  Evidence for central timing of rhythmical mastication , 1971, The Journal of physiology.

[3]  E. Luschei,et al.  Effects of destroying spindle afferents from jaw muscles on mastication in monkeys. , 1974, Journal of Neurophysiology.

[4]  Y. Lamarre,et al.  Load compensation in human masseter muscles. , 1975, The Journal of physiology.

[5]  G Hellsing,et al.  A tonic vibration reflex evoked in the jaw opening muscles in man. , 1977, Archives of oral biology.

[6]  Ph. D. Ronald Dubner D. D. S.,et al.  The Neural Basis of Oral and Facial Function , 1978, Springer US.

[7]  Ronald Dubner,et al.  The Neural Basis of Oral and Facial Function , 1978 .

[8]  Y. Lamarre,et al.  The distribution of golgi tendon organs and muscle spindles in masseter and temporalis muscles of the cat , 1978, Neuroscience.

[9]  P. Neilson,et al.  Tonic stretch reflexes in lip, tongue and jaw muscles , 1979, Brain Research.

[10]  B. Lennartsson.  Muscle spindles in the human anterior digastric muscle. , 1979, Acta odontologica Scandinavica.

[11]  R. Dubner,et al.  Oral-facial sensory and motor functions , 1981 .

[12]  Y. Lamarre,et al.  Human jaw reflexes. , 1983, Advances in neurology.

[13]  Y. Lamarre,et al.  Rapid elbow flexion in the absence of proprioceptive and cutaneous feedback. , 1987, Human neurobiology.

[14]  J. Hellgren,et al.  A physiological study of the monosynaptic reflex responses of cat spinal α-motoneurons after partial lumbosacral deafferentation , 1989, Brain Research.

[15]  A Struppler,et al.  Discharge pattern of tonically activated motor units during unloading. , 1990, Electromyography and clinical neurophysiology.

[16]  A. Rowlerson,et al.  Specialization of Mammalian Jaw Muscles: Fibre Type Compositions and the Distribution of Muscle Spindles , 1990 .

[17]  A. Taylor.  Neurophysiology of the Jaws and Teeth , 1990 .

[18]  S. Landgren,et al.  Primary Afferent and Descending Cortical Convergence on the Interneurons in the Border Zone of the Trigeminal Motor Nucleus: A Comparison between Trigeminal and Spinal Interneurons , 1990 .

[19]  J. Kaas.  Plasticity of sensory and motor maps in adult mammals. , 1991, Annual review of neuroscience.

[20]  A Smith,et al.  The control of orofacial movements in speech. , 1992, Critical reviews in oral biology and medicine : an official publication of the American Association of Oral Biologists.

[21]  M. Latash.  Control of human movement , 1993 .

[22]  D. Ostry,et al.  Control of jaw orientation and position in mastication and speech. , 1994, Journal of neurophysiology.

[23]  A G Hannam,et al.  Internal organization in the human jaw muscles. , 1994, Critical reviews in oral biology and medicine : an official publication of the American Association of Oral Biologists.

[24]  A. G. Feldman,et al.  The origin and use of positional frames of reference in motor control , 1995, Behavioral and Brain Sciences.

[25]  David J. Ostry,et al.  The control of multi-muscle systems: human jaw and hyoid movements , 1996, Biological Cybernetics.