Difference between revisions of "4° Clinical case: Temporomandibular disorders"

===== Silent period of the masticator muscles =====

Figure 4 shows the neuromuscular responses of the silent period to chin percussion through a triggered neurological hammer when the patient was asked to clench her teeth maximally. If from a neurological point of view it is not possible to highlight elements referable to organic alterations of the _tCNS, some electrophysiological characteristics, however, are to be referred to a functional disorder of the system. In the upper trace, a decrease in the motor neuron reactivation phase can be seen immediately following the silent period. The possible neurophysiological mechanism capable of determining a similar decrease in facilitatory activities on the mandibular silent period can be ascribed to a change in the spindle motor drive induced by the input of muscle proprioceptors and nociceptors. The neuronal network of this process would take place through a loop formed by: muscle nociceptive afferents, the subnucleus caudalis of the V, inhibitory interneurons on static motor neurons and, as a last link, the modulation of the sensitivity of the neuromuscular spindles..<ref>Ro J.Y.,Capra  N.F.: Physiological evidence for caudal brainstem projections of jaw muscle spindle afferents.Exp.Brain Res 1999;128: 425-434</ref> <ref>Capra N.F.,Ro J.Y.: Experimental muscle pain produces central modulation of proprioceptive signals arising from jaw muscle spindles. Pain 2000; 86: 151-162.</ref><ref>Appelberg B.,Hulliger M.,Johansson H.Sojka P.: Actions on g-motoneurones elicited by electrical stimulation of group III muscle afferent fibers in the hind limb of the cat.J Physiol. 1983;335: 275-292.</ref><ref>Macefield  G.,Hagbarth E,Gorman R, Gandevia SC,, Burke D.: Decline in spindle support to a-motoneurones during sustained voluntary contractions.J.Physiol 1991;440:497-512.</ref><ref>Mense S.,Skeppar P.: Discharge behavior of feline gamma-motoneurones following induction of an  artificial myositis.Pain 1991; 46: 201-210.</ref><ref>Pedersen J, Ljubisavljevic M, Bergenheim M.,Johansson H.: Alterations in information trasmission  in ensembles  of primary muscle spindle afferents after muscle fatigue in heteronymous muscle.Neuroscience 1998;84: 953-959.</ref>  Also in this context the inhibitory component most likely prevails over the excitatory one and this could be ascribed to a malocclusion as we will see later. In particular, it can be noted the overlapping of the jaw jerk behavior, previously tested, in a path rectification condition. The arrow indicates the jaw jerk on all traces and the decrease in amplitude can be observed for the right masseter while it is relatively symmetrical on the temporal muscles.<br />