View source for Trigeminal Nervous System Segmentation/fr

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Partons d'une considération simple: l'interprétation des signaux cryptés des activités neuronales est une tâche complexe et courageuse. 
Cependant, en appliquant une stratégie de simplification, nous pouvons déduire des données intéressantes qui peuvent nous aider à comprendre le "comportement émergent" du système lui-même. 

Nous avons déjà expliqué que les systèmes indéterminés doivent être stimulés par un déclencheur externe pour pouvoir être étudiés. Cela signifie que nous devons également être conscients de la nature du stimulus: il doit être connu à l'avance et bien calibré, car une stimulation sous-seuil pourrait générer un type de réponse du SNC, tandis qu'une autre réponse supra-seuil irait vers une réponse saturée.

[[File:Gray778 Trigeminal.png|thumb|Le nerf trijumeau]]
La segmentation de la partie du SNC impliquée dans la fonction de mastication aboutit à la diviser en trois macro-zones: 
*l'''aire corticale'' (dans laquelle la réponse de l'action motrice trigéminale se produit - c'est-à-dire l'aire corticale trigéminale); 
*la ''zone périphérique'', où la réponse de la racine trigéminale est analysée; et 
*<span lang="en" dir="ltr" class="mw-content-ltr">the ''brainstem-pontine-related area'', which is involved in a broad genesis of trigeminal reflexes</span>.

{{ArtBy|autore=Gianni Frisardi}}

===Zone corticale trigéminale===

<span lang="en" dir="ltr" class="mw-content-ltr">When we try to assess the integrity and/or symmetry of the Trigeminal Motor Cortex (TMC), we certainly cannot completely trust the MR imaging techniques because they lack data about ‘functionality’</span>: <span lang="en" dir="ltr" class="mw-content-ltr">the image symmetry of the trigeminal motor cortical areas does not results in functional symmetry, even if we could try a kind of comparison with the functional MRI (fMR)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This latest technology, however, is unlikely to be extemporaneous, because the speed of activation of neuronal excitability is too high</span>. <span lang="en" dir="ltr" class="mw-content-ltr">As a result, we are forced to employ electrophysiological stimulation techniques to evoke a response from the pyramidal bundle coming from neurons of the first order pf the TMC</span> (Figure 1). 
[[File:Trigeminal Cortical Area - C-MEPs.jpg|thumb|'''Figure 1:''' <span lang="en" dir="ltr" class="mw-content-ltr">Transcranial Magnetic Stimulation</span> |400px|left]]

<span lang="en" dir="ltr" class="mw-content-ltr">Nowadays electrical transcranial stimulation is no longer used; it has been replaced by the Magnetic Transcranial Stimulation or Stimulation</span> <sub>m</sub>TCS.

===<span lang="en" dir="ltr" class="mw-content-ltr">Magnetic Transcranial Stimulation</span> (mTCS)===

<span lang="en" dir="ltr" class="mw-content-ltr">In our laboratories, this procedure requires a unique experiment in which the electrodes are positioned on the patient and a series of tests is carried out, including</span>:
*<span lang="en" dir="ltr" class="mw-content-ltr">the magnetic Transcranial Stimulation</span> <sub>m</sub>TCS,
*<span lang="en" dir="ltr" class="mw-content-ltr">trigeminal reflexes</span>, et 
*<span lang="en" dir="ltr" class="mw-content-ltr">the Electric Transcranial Stimulation of the trigeminal Root</span> <sub>e</sub>TCS, <span lang="en" dir="ltr" class="mw-content-ltr">as described below</span>.

<span lang="en" dir="ltr" class="mw-content-ltr">In Figure 10, we can understand the genesis of the <sub>m</sub>TCS and subsequent neuromotor responses named '''Cortex-Motor Evoked Potentials''' (C-MEPs) elicited by an induced current within the brain tissue</span>; <span lang="en" dir="ltr" class="mw-content-ltr">this current was determined by the magnetic field crossed from a coil placed on the subject’s skull vertex</span>. <span lang="en" dir="ltr" class="mw-content-ltr">As a routine, we use a Magstim BiStim<sup>2</sup> magnetic stimulator (Magstim Ltd, UK), attached to a circular coil (external diameter 10 cm), for magnetic fields up to 2 T (exit 100%)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The intensity of stimulation is expressed as a percentage of the maximum power</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The magnetic coil is positioned flat on the scalp</span>; <span lang="en" dir="ltr" class="mw-content-ltr">the optimum position is on the medial line, with the centre of the coil slightly forward to the top</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This position is capable of evoking a motor action potential on both the masseter muscle, without evident depolarization of the trigeminal root</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In order to evoke a Cortex-MEPs, subjects need to exercise a mild mandibular closure with EMG activity</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The latency at the onset and the peak-to-peak width are measured at least on six tests</span><ref>{{cita libro 
 | autore = Cruccu G
 | autore2 = Berardelli A
 | autore3 = Inghilleri M
 | autore4 = Manfredi M
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = Functional organization of the trigeminal motor system in man. A neurophysiological study
 | url = https://pubmed.ncbi.nlm.nih.gov/2804615/
 | volume = 
 | opera = Brain
 | anno = 1989
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1093/brain/112.5.1333 
 | OCLC = 
 }}</ref>.

===<span lang="en" dir="ltr" class="mw-content-ltr">Trigeminal Nervous System excitability</span>===

<span lang="en" dir="ltr" class="mw-content-ltr">Transcranial magnetic stimulation activates the primary motor cortex by excitating the interneural fibres that project on pyramidal cells</span>; <span lang="en" dir="ltr" class="mw-content-ltr">it also evocates short series of potential of action called Indirect or I-waves</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Magnetic high-intensity shocks can also depolarize the assonal portion of the pyramidal cells stimulating mixed events, including a direct D-wave action potential and some Indirect waves (I-wave)</span><ref name="roth">{{cita libro 
 | autore = Rothwell JC
 | autore2 = Thompson PD
 | autore3 = Day BL
 | autore4 = Boyd S
 | autore5 = Marsden CD
 | autore6 = 
 | autore7 = 
 | titolo = Stimulation of the human motor cortex through the scalp
 | url = https://physoc.onlinelibrary.wiley.com/doi/epdf/10.1113/expphysiol.1991.sp003485
 | volume = 
 | opera = Exp Physiol
 | anno = 1991
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1113/expphysiol.1991.sp003485 
 | OCLC = 
 }}</ref>. 

<span lang="en" dir="ltr" class="mw-content-ltr">The stimulation of the facial motor cortex evokes a descendant burst</span>; <span lang="en" dir="ltr" class="mw-content-ltr">this burst travels along the corticobulbar tract and reaches the trigeminal and facial motorneurons with a multi-synaptic connection</span>, <span lang="en" dir="ltr" class="mw-content-ltr">whereas there is a monosynaptic and almost completely controlateral connection at the masseteric motorneurons that is similar to the corticospinal projection on motor neurons of the hand muscles</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Pre-innervation has also to be acknowledged when we have to deal with the trigeminal system</span>: <span lang="en" dir="ltr" class="mw-content-ltr">even with high intensity magnetic stimulation, no motor potential can be evoked without contracting the target muscles</span>. <span lang="en" dir="ltr" class="mw-content-ltr">During the contraction, potential masseterics show shorter latency, short duration, and synchronous responses, which reach an amplitude of approximately 30% of the motor response from direct stimulation of the masseter nerve named M-wave</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">Motoneuronal activation follows the principle of the section</span>: <span lang="en" dir="ltr" class="mw-content-ltr">the smaller motorneurons are activated first</span><ref name="roth" />. <span lang="en" dir="ltr" class="mw-content-ltr">Masseteric motorneurons show normal excitability when they are triggered by the stimulation from the motor cortex</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Schwartz and Lund (1995) have recently studied the effect of nociceptive pressure on the mandibular movement and the EMG activity of the masseter in decerebrated rabbits</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The motoneurons stimulated the corticobulbar tract through the same path, but the two entrances differed</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In our experiments the short-lived high frequency discharge of action potential is of a phasic type, even if in the works of Schwartz and Lund</span><ref>{{cita libro 
 | autore = Schwartz G
 | autore2 = Lund JP
 | titolo = Modification of rhythmical jaw movements by noxious pressure applied to the periosteum of the zygoma in decerebrate rabbits
 | url = https://pubmed.ncbi.nlm.nih.gov/8628580/
 | volume = 
 | opera = Pain
 | anno = 1995
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/0304-3959(95)00028-q 
 | OCLC = 
 }}</ref>, <span lang="en" dir="ltr" class="mw-content-ltr">the potentials for action are tonic</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In their experiments on tonic pain, the amplitude of mandibular movements and the recruitment of the masseteric motorneurons decrease. However, we can exclude a greater excitability all along the path from the motor cortex to the lower motorneurons</span>.

===<span lang="en" dir="ltr" class="mw-content-ltr">Trigeminal Peripheral Area</span>===
[[File:Bilateral Root-MEPs.jpg|left|thumb|'''Figure 2:''' <span lang="en" dir="ltr" class="mw-content-ltr">bilateral Root-MEPs</span>]]
<span lang="en" dir="ltr" class="mw-content-ltr">When we need to assess the integrity of the trigeminal roots, we should evoke a motor action potential of the peripheral trigeminal motor tract in a synchronous and symmetrical way</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In this situation, a <sub>m</sub> TCS is not suggested</span>: <span lang="en" dir="ltr" class="mw-content-ltr">it would rather be advisable to adopt the bilateral electric stimulation routines called <sub>bilaterally</sub>Root-MEPs technology that we fine-tuned in our neurophysiology laboratories</span><ref>{{cita libro 
 | autore = Frisardi G
 | titolo = The use of transcranial stimulation in the fabrication of an occlusal splint
 | url = https://pubmed.ncbi.nlm.nih.gov/1501190/
 | volume = 
 | opera = J Prosthet Dent
 | anno = 1992.
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/0022-3913(92)90345-b 
 | OCLC = 
 }}</ref>. 

<span lang="en" dir="ltr" class="mw-content-ltr">In order to achieve this target, synchronicity, symmetry, and the pulse maximum power are essential</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This is why electromyographers must be used for evoked potential and they must be equipped with two independent and autonomous high voltage electrostimulators</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The EMGs that employ tools with a single multiplexated electrostimulator to deliver two or more stimuli are not appropriated</span>: <span lang="en" dir="ltr" class="mw-content-ltr">the second impulse would lose synchronicit, because the condensers need time to recharge</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 2).

[[File:FEM.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 3:''' <span lang="en" dir="ltr" class="mw-content-ltr">Electrophysiological procedure for trigeminal evoked potentials and intracranial diffusion of the induced electric field</span>. ]]
<span lang="en" dir="ltr" class="mw-content-ltr">We carry out an analysis made through a generic finite element processor (FE, SimNibs method) to study the distribution of the electric field within the intracranial brain tissue, even if only as a descriptive model</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 3)<ref>{{cita libro 
 | autore = Windhoff M
 | autore2 = Opitz A
 | autore3 = Thielscher A
 | titolo = Electric field calculations in brain stimulation based on finite elements: An optimized processing pipeline for the generation and usage of accurate individual head models
 | url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6870291/pdf/HBM-34-923.pdf
 | volume = 
 | opera = Hum Brain Mapp
 | anno = 2013
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1002/hbm.21479
 | OCLC = 
 }}</ref>.

<span lang="en" dir="ltr" class="mw-content-ltr">The EF models of the study consist of about 1.7 million tetrahedra</span>. T<span lang="en" dir="ltr" class="mw-content-ltr">he Mesh resolution was selectively improved in the regions of the Grey Matter (GM), White Matter (WM), skull, and cerebrospinal fluid (CSF), with an average tetrahedron volume of 1 mm</span><sup>3</sup>. 

<span lang="en" dir="ltr" class="mw-content-ltr">Electrical conductibility has been assigned to different types of the affected tissues in which</span> 

<math>\sigma_{Skin} =0.465 S/m;\sigma_{Skull} =0.010 S/m;\sigma_{CSF} =1.654 S/m;\sigma_{GM} =0.276 S/m;\sigma_{WM} =0.126 S/m; </math><ref>{{cita libro 
 | autore = Thielscher A
 | autore2 = Opitz A
 | autore3 = Windhoff M
 | autore4 = 
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = Impact of the gyral geometry on the electric field induced by transcranial magnetic stimulation
 | url = https://pubmed.ncbi.nlm.nih.gov/20682353/
 | volume = 
 | opera = Neuroimage
 | anno = 2011
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/j.neuroimage.2010.07.061 
 | OCLC = 
 }}</ref>. 

<span lang="en" dir="ltr" class="mw-content-ltr">Figure 3A shows the position of the electrodes</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 12A); <span lang="en" dir="ltr" class="mw-content-ltr">the maximum current will spread under the cathodes (red in colour) in the parietal cortex</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 3B); <span lang="en" dir="ltr" class="mw-content-ltr">in the cranial cortex region, near the trigeminal motor root, the current density is of low magnitude</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 3C, <span lang="en" dir="ltr" class="mw-content-ltr">black arrows</span>). <span lang="en" dir="ltr" class="mw-content-ltr">Figure 3D shows the current density that spreads in the brain tissue</span>. <span lang="en" dir="ltr" class="mw-content-ltr">It underlines the least amount of electrical current within the brain tissue necessary to saturate the trigeminal motor (relative to the amount required to evoke a response of the trigeminal motor cortex under the cathode)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This is one of the reasons that urged us to choose this kind of evoked response (absolutely peripheral) rather than the cortical one</span> (<span lang="en" dir="ltr" class="mw-content-ltr">with higher threshold, lower stability, and less focus</span>).

<span lang="en" dir="ltr" class="mw-content-ltr">With this approach we concluded that, given the emergence of the trigeminal root in oval foramen and the distance from the parietal bone and parietal cortical area, the cathode positioning should be more caudal than the regulation</span> (11–<span lang="en" dir="ltr" class="mw-content-ltr">13 cm on the acoustic-meacoustic line</span>): <span lang="en" dir="ltr" class="mw-content-ltr">immediately above the upper edge of the ear</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The position of the cathode, therefore, will be approximately more than the starndard 13–15 cm and will be delimited by the upper margin of the ear</span>.

<span lang="en" dir="ltr" class="mw-content-ltr">Considering the safety limits, the energy provided for each individual impulse in our application will follow this formula</span>:

<math>E=\bigtriangleup t =R \times I^2  \times \bigtriangleup t = 2.5 mJ  </math>per impuls.[[File:Potenziale Evocato della Radice Trigeminale.jpg|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 4:''' <span lang="en" dir="ltr" class="mw-content-ltr">By increasing the stimulus delivery, more fibers are gradually recruited until saturation</span>.]]

<span lang="en" dir="ltr" class="mw-content-ltr">About the simultaneous use of the two electrostimulators — from the safety point of view  — the limits turn out to have been 10 times lower than those indicated in the IEC legislation</span>.

<span lang="en" dir="ltr" class="mw-content-ltr">The electrodes are arranged as follows</span>: 

* <span lang="en" dir="ltr" class="mw-content-ltr">Cathode electrode has been placed on each side at 13–15 cm along the line conjoining the vertex - acoustic meatus in the bilaterally parietal region</span>. 
* <span lang="en" dir="ltr" class="mw-content-ltr">The electrical stimulus consists of a square wave which length is 0.250 ms, at a voltage of 300 V and a maximum current of 100 mA</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">Hence, the first procedure is to check the saturation of the motor response of the trigeminal root</span>. 
*<span lang="en" dir="ltr" class="mw-content-ltr">At 20 mA, 30 mA, and 40 mA, we can observe a latency of 2.4 ms, 2.4 ms, and 2.3 ms respectively, but on increasing the amperage, we can observe a decrease in latency up to 2.1 ms at 50 mA, 2 ms at 70 mA, and 1.9 ms at 80 mA, 90 mA, and 100 mA</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 3). 
*<span lang="en" dir="ltr" class="mw-content-ltr">These latency differences reach up to a maximum current density, depending on the capacitive components and resistance of the tissues to the current flow</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">The saturation of the electrophysiological signal evoked by the trigeminal root is the first absolute and mandatory step that needs to be performed, even before clinical interpretation</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The saturation of the evoked potentials from the trigeminal root showed no change in amplitude</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Matter of fact, when the electrostimulator reaches 80 mA pulses, 90 mA, and 100 mA, the P-P amplitude stabilizes at 4.6 mV</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 4). <span lang="en" dir="ltr" class="mw-content-ltr">The amplitude value of 4.6 mV (of course, the amplitude can be chosen to the integral area or vice versa, depending on the purpose of the study) is to be considered the ‘''Maximum Absolute value of Neural Evoked Energy''’ from the trigeminal motor system</span>. <span lang="en" dir="ltr" class="mw-content-ltr">It is called</span> '''‘<sub>m</sub>ANEE’'''.
 
[[File:Test trigeminali.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 5:''' <span lang="en" dir="ltr" class="mw-content-ltr">Tests mainly used in trigeminal neurophysiopathology</span>]]

===<span lang="en" dir="ltr" class="mw-content-ltr">Trigeminal Brainstem Area</span>===
<span lang="en" dir="ltr" class="mw-content-ltr">The trigeminal brainstem area is the most complex area to study and interpret because of the complexity of its multi-synaptic connections</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The following electro-physiological tests are objectively sufficient to understand the cryptic language of the SCNS</span>. <span lang="en" dir="ltr" class="mw-content-ltr">These will be treated in this section, but they will also be resumed in other editions</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The following trigeminal reflexes will be considered</span>: <span lang="en" dir="ltr" class="mw-content-ltr">the ''jaw jerk'', the ''mechanical and electrical silent period'', the ''recovery cycle of the masseteric inhibitory reflex'' and the ''laser silent period'', as well as the ''masseteric laser-evoked potentials''</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 5).

====<span lang="en" dir="ltr" class="mw-content-ltr">Jaw jerk Reflex</span>====
[[File:Riflesso mandibolare.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 6:''' <span lang="en" dir="ltr" class="mw-content-ltr">Mandibular reflex performed with Nihon Kohden instrumentation</span>]]
<span lang="en" dir="ltr" class="mw-content-ltr">The piezoelectric trigger is used for the mandibular reflex, though it does not provide controlled reproducibility and quantification of the stimulation intensity</span>; <span lang="en" dir="ltr" class="mw-content-ltr">simultaneous recordings of the two sides are considered an essential method for the accurate and acceptable assessment of the asymmetry of the side</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Asymmetry in the latency is very small: it ranges from 0 to 0.8 ms with an average of 0.13 ms (SD 0.17) in 131 normal subjects</span><ref>{{cita libro 
 | autore = Kimura J
 | autore2 = Daube J
 | autore3 = Burke D
 | autore4 = Hallett M
 | autore5 = Cruccu G
 | autore6 = Ongerboer de Visser BW
 | autore7 = Yanagisawa N
 | autore8 = Shimamura M
 | autore9 = Rothwell J
 | titolo = Human reflexes and late responses. Report of an IFCN committee
 | url = https://pubmed.ncbi.nlm.nih.gov/7515783/
 | volume = 
 | opera = Electroencephalogr Clin Neurophysiol
 | anno = 1994
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/0013-4694(94)90131-7 
 | OCLC = 
 }}</ref>. <span lang="en" dir="ltr" class="mw-content-ltr">Although in trigeminal neuropathy or multiple sclerosis the jaw jerk reflex may be retarded by several milliseconds, asymmetries of latency of only 0.8 ms were considered to be a higher limit of normality in neurological studies</span> (Figure 6).

<span lang="en" dir="ltr" class="mw-content-ltr">In previous studies about the jaw jerk in patients with cranial-mandibular disorders (TMDs), patients with ''unilateral'' disorders were selected to identify an affection side in which there was a latency delay and a lower amplitude on the side of the mandibular deviation and pain</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Even if the maximum mandibular closure force in TMDs can be reduced to half as much as control groups, several researchers propose that muscular hyperactivity is one of the key mechanisms in cranial-mandibular dysfunction, and that hyperactivity of the masticatory muscles is central to the nervous system</span><ref>{{cita libro 
 | autore = Molin C
 | titolo = Vertical isometric muscle forces of the mandible. A comparative study of subjects with and without manifest mandibular pain dysfunction syndrome 
 | url = https://pubmed.ncbi.nlm.nih.gov/4569754/
 | volume = 
 | opera =  Acta Odontol Scand
 | anno = 1972
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.3109/00016357209002499 
 | OCLC = 
 }}</ref>. <span lang="en" dir="ltr" class="mw-content-ltr">A cortical activity or abnormal reticular system would increase the excitability of the motorneurons directly through the corticobulbar system or indirectly through the modulation of multi-synaptic reflexes of lateral reticular formation. The initial causes could be stress, psychogenic factors, or a primary disease of the central nervous system, such as the oromandibular dystonia</span><ref>{{cita libro 
 | autore = Yemm R
 | autore2 = 
 | autore3 = 
 | autore4 = 
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = Neurophysiologic studies of temporomandibular joint dysfunction
 | url = https://pubmed.ncbi.nlm.nih.gov/775370/
 | volume = 
 | opera = Oral Sci Rev
 | anno = 1976
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 
 | OCLC = 
 }}</ref><ref>{{cita libro 
 | autore = Cruccu G
 | autore2 = Pauletti G 
 | autore3 = Agostino R
 | autore4 = Berardelli A
 | autore5 = Manfredi M
 | titolo = Masseter inhibitory reflex in movement disorders. Huntington's chorea, Parkinson's disease, dystonia, and unilateral masticatory spasm
 | url = https://pubmed.ncbi.nlm.nih.gov/1705216/
 | volume = 
 | opera = Electroencephalogr Clin Neurophysiol
 | anno = 1991
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 
 | OCLC = 
 }}</ref>. 

<span lang="en" dir="ltr" class="mw-content-ltr">The afferents from group II in the division of the maxillary and mandibular trigeminal nerve apply a powerful inhibition of the motoneurons of the mastication muscles through synaptic and polysynaptic reflexes</span>. <span lang="en" dir="ltr" class="mw-content-ltr">A remarkable feature of the mandibular reflexes, however, is their bilateral symmetry</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In some patients with multiple sclerosis (MS) the latency is prolonged, whereas it lacks in others: this reflex can sometimes be essential for diagnosing the lesions of the brainstem in MS</span>. <span lang="en" dir="ltr" class="mw-content-ltr">It might also be more effective for therapy</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 6).

====<span lang="en" dir="ltr" class="mw-content-ltr">Masseteric Mechanical Silent Period</span>====
[[File:PSM_-_Masseter_mechanical_Silent_Period.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 7:''' <span lang="en" dir="ltr" class="mw-content-ltr">Representation of a typical masseteric inhibitory reflex</span> (MSP) ]]
<span lang="en" dir="ltr" class="mw-content-ltr">The jaw jerk is a short-latency excitatory reflection that can be evoked by a stretch of the mandibular elevators through a percussion produced by a triggered neurological hammer</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The excitation on motoneurons <code>α</code> from the neuromuscular spindles is the only generally accepted explanation</span>. <span lang="en" dir="ltr" class="mw-content-ltr">When this type of mechanical stimulus is applied during voluntary activation EMG (i.e., by pressing the teeth), the jaw overlaps with the Interference  EMG activity, and is followed by a period of absence or depression of the electromyographic activity, the so-called '''Masseteric Silent Period'''</span> (MSP)<ref>{{cita libro 
 | autore = Goldberg LJ
 | titolo = Masseter muscle excitation induced by stimulation of periodontal and gingival receptors in man
 | url = https://pubmed.ncbi.nlm.nih.gov/5134584/
 | volume = 
 | opera = Brain Res
 | anno = 1971
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/0006-8993(71)90330-1 
 | OCLC = 
 }}</ref> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 7). 

<span lang="en" dir="ltr" class="mw-content-ltr">The MSP has sparked particular interest as it has been shown that the duration of the silent period is higher in patients with TMDs</span><ref>{{cita libro 
 | autore = Widmalm SE
 | titolo = The silent period in the masseter muscle of patients with TMJ dysfunction
 | url = https://www.tandfonline.com/doi/abs/10.3109/00016357609026557?journalCode=iode20
 | volume = 
 | opera = Acta Odontol Scand
 | anno = 1976
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.3109/00016357609026557
 | OCLC = 
 }}</ref><ref>{{cita libro 
 | autore = Brenman HS
 | autore2 = Black MA
 | autore3 = Coslet JG
 | titolo = Interrelationship between the electromyographic silent period and dental occlusion
 | url = https://pubmed.ncbi.nlm.nih.gov/5240811/
 | volume = 
 | opera = J Dent Res
 | anno = 1968
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1177/00220345680470033301 
 | OCLC = 
 }}</ref>. <span lang="en" dir="ltr" class="mw-content-ltr">This period of depression or absence of EMG activity can be caused by various active inhibitory influences, but it can also be caused by synchronization of the a motoneurons after the initial efferent volley</span>.

<span lang="en" dir="ltr" class="mw-content-ltr">The criteria for clinical evaluation remain unclear: there is still a certain confusion about both measurement and reported values, which vary considerably in different studies</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Klineberg and collaborators provoked a percussion on the chin through the use of a standardized solenoid in 10 healthy subjects during mass isometric activity: it generated a vertical movement that was parallel to the surface fibres of the superficial muscle of the masseter muscle, and they after analysed the mechanical silent period</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The reflection evoked the classic jaw jerk in short latency (mean, 8.3 ms) followed by an SP (average latency, 15.9 ms, average duration, 42.6 ms)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The duration of the SP greatly varies not only between subjects, but also within individuals</span><ref>{{cita libro 
 | autore = Hellsing G
 | autore2 = Klineberg I 
 | autore3 = 
 | autore4 = 
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = The masseter muscle: the silent period and its clinical implications
 | url = https://www.sciencedirect.com/science/article/abs/pii/0022391383902494
 | volume = 
 | opera = J Prosthet Dent
 | anno = 1983
 | editore = University of Sydney, Faculty of Dentistry
 | città = Sydney, New South Wales, Australia
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/0022-3913(83)90249-4
 | OCLC = 
 }}</ref>.

====<span lang="en" dir="ltr" class="mw-content-ltr">Recovery Cycle of Masseteric Inhibitory Reflex</span>====
[[File:CR_MIR_masseter_inhibitory_recovery_cycle_reflex.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 8:''' <span lang="en" dir="ltr" class="mw-content-ltr">Representation of the masseteric inhibitory reflex recovery cycle</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Note the pair of electrical stimuli (S1 and S2) and the corresponding silent periods</span> (ES1 et ES2)]]
<span lang="en" dir="ltr" class="mw-content-ltr">Headache is oftes associated with a ‘sensitization’ of the nociceptive trigeminal system with the involvement of anti-nocicective mesenchephalic structures such as periaqueductal substance, locus coeruleus, and the nuclei of the raphe, which have a modulator effect on trigeminal sensitive nuclei</span><ref>{{cita libro 
 | autore = Holle D 
 | autore2 = Obermann M
 | autore3 = Katsarava Z
 | titolo = The electrophysiology of cluster headache
 | url = https://pubmed.ncbi.nlm.nih.gov/19272282/
 | volume = 
 | opera = Curr Pain Headache Rep
 | anno = 2009
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1007/s11916-009-0026-9 
 | OCLC = 
 }}</ref>.

<span lang="en" dir="ltr" class="mw-content-ltr">The descending modulator effect from these nuclei has been shown through experimental studies on animals, and the temporary trigeminal ‘sensitization’ effect during hemicranic attack has been shown to be clinically demonstrated through electrophysiological studies</span><ref>{{cita libro 
 | autore = Yan J
 | autore2 = Melemedjian OK 
 | autore3 = Price TJ
 | autore4 = Dussor G
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = Sensitization of dural afferents underlies migraine-related behavior following meningeal application of interleukin-6 (IL-6)
 | url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274468/
 | volume = 
 | opera = Mol Pain
 | anno = 2012
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI =  10.1186/1744-8069-8-6 
 | OCLC = 
 }}</ref>. <span lang="en" dir="ltr" class="mw-content-ltr">The most credited hypothesis considers the dysfunction of anti-nocicadjective nuclei as the cause of a disinhibition of the trigeminal nociceptive system</span><ref>{{cita libro 
 | autore = Hansen PO
 | autore2 = Svensson P
 | autore3 = Arendt-Nielsen L
 | autore4 = Jensen TS
 | titolo = Human masseter inhibitory reflexes evoked by repetitive electrical stimulation
 | url = https://pubmed.ncbi.nlm.nih.gov/11856628/
 | volume = 
 | opera = Clin Neurophysiol
 | anno = 2002
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1016/s1388-2457(01)00729-5 
 | OCLC = 
 }}</ref>. 

<span lang="en" dir="ltr" class="mw-content-ltr">Orofacial pain, including algies from TMDs, appears to have a modulation effect on the mandibular reflexes</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Electrophysiological studies have shown that the experimentally induced pain by infusion of saline hypertonic solution to 5% in the masseter results in an increase in the peak-to-peak size of the jaw spider</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This facilitatory effect seems to be related to the increased sensitivity of the fusimotor system, which causes muscle stiffness</span><ref>{{cita libro 
 | autore = Truini A
 | autore2 = Romaniello A
 | autore3 = Svensson P
 | autore4 = Galeotti F
 | autore5 = Graven-Nielsen T
 | autore6 = Wang K
 | autore7 = Cruccu G
 | autore8 = Arendt-Nielsen L
 | titolo = Experimental skin pain and muscle pain induce distinct changes in human trigeminal motoneuronal excitability
 | url = https://pubmed.ncbi.nlm.nih.gov/16733707/
 | volume = 
 | opera = Exp Brain Res
 | anno = 2006
 | editore = 
 | città = 
 | ISBN = 
 | LCCN = 
 | DOI = 10.1007/s00221-006-0508-5 
 | OCLC = 
 }}</ref>.

<span lang="en" dir="ltr" class="mw-content-ltr">Other animal studies have been carried out in the experimentally induced muscle pain, demonstrating that the activation of muscle nociceptors  markedly influences the proprioceptive properties of neuromuscular fusis through a central neural pathway</span>.<ref>{{cita libro 
 | autore = Louca S
 | autore2 = Christidis N
 | autore3 = Ghafouri B
 | autore4 = Gerdle B
 | autore5 = Svensson P
 | autore6 = List T
 | autore7 = Ernberg M
 | titolo = Serotonin, glutamate and glycerol are released after the injection of hypertonic saline into human masseter muscles – a microdialysis study
 | url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4293545/pdf/1129-2377-15-89.pdf
 | volume = 
 | opera = J Headache Pain
 | anno = 2014
 | editore = 
 | città = 
 | ISBN = 
 | DOI = 
 | oaf = sì
 | OCLC = 
 }}</ref> <span lang="en" dir="ltr" class="mw-content-ltr">However, the washing of the local algogena substance leads to a return to normality of the tendon reflexes</span>. <span lang="en" dir="ltr" class="mw-content-ltr">In pain from TMDs, there is a dichotomy between schools of thought: while one school proposes an ‘hyperactivity’ effect of the central nervous system</span> (CNS: <span lang="en" dir="ltr" class="mw-content-ltr">Central Nervous System</span>), <span lang="en" dir="ltr" class="mw-content-ltr">the other suggests a normal excitability of the trigeminal nervous system</span><ref>{{cita libro 
 | autore = Xu W
 | autore2 = Wu Y
 | autore3 = Bi Y
 | autore4 = Tan L
 | autore5 = Gan Y
 | autore6 = Wang K
 | autore7 = 
 | titolo = Activation of voltage-gated KCNQ/Kv7 channels by anticonvulsant retigabine attenuates mechanical allodynia of inflammatory temporomandibular joint in rats
 | url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2936374/pdf/1744-8069-6-49.pdf
 | volume = 
 | opera = Mol Pain
 | anno = 2010
 | editore = 
 | città = 
 | ISBN = 
 | DOI = 10.1186/1744-8069-6-49
 | oaf = yes
 | LCCN = 
 | OCLC = 
 }}</ref><ref>{{cita libro 
 | autore = Cruccu G
 | autore2 = Frisardi G
 | autore3 = van Steenberghe D
 | autore4 = 
 | autore5 = 
 | autore6 = 
 | autore7 = 
 | titolo = Side asymmetry of the jaw jerk in human craniomandibular dysfunction
 | url = https://pubmed.ncbi.nlm.nih.gov/1520092/
 | volume = 
 | opera = Arch Oral Biol
 | anno = 1992
 | editore = 
 | città = 
 | ISBN = 
 | DOI = 10.1016/0003-9969(92)90047-c 
 | oaf = <!-- qualsiasi valore -->
 | LCCN = 
 | OCLC = 
 }}</ref>. 

'''<span lang="en" dir="ltr" class="mw-content-ltr">Bruxism</span>''' <span lang="en" dir="ltr" class="mw-content-ltr">is usually believed to be related to musculoskeletal pain, such as pain from TMDs, but also to muscular-tensive headache</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Few studies have actually tried to fully describe the pain associated with bruxism examining the neurobiological and physiological characteristics of the mandibular muscles</span>. <span lang="en" dir="ltr" class="mw-content-ltr">There are some clinical cases in the literature and small studies suggesting that some drugs related to dopaminergic, serotonergic, and adrenergic systems, can both suppress and exacerbate bruxism</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Most of the pharmacological studies mentioned before indicate that several classes of medications can affect muscle activity related to bruxism without having any effect on Orofacial Pain</span> (OP: <span lang="en" dir="ltr" class="mw-content-ltr">Orofacial pain</span>)<ref>{{cita libro 
 | autore = Winocur E
 | autore2 = Gavish A
 | autore3 = Voikovitch M
 | autore4 = Emodi-Perlman A
 | autore5 = Eli I
 | autore6 = 
 | autore7 = 
 | titolo = Drugs and bruxism: a critical review 
 | url = https://pubmed.ncbi.nlm.nih.gov/12836498/
 | volume = 
 | opera = J Orofac Pain
 | anno = 2003
 | editore = Tel Aviv University
 | città = Tel Aviv, Israel
 | ISBN = 
 | DOI = 
 | oaf = <!-- qualsiasi valore -->
 | LCCN = 
 | OCLC = 
 }}</ref>. <span lang="en" dir="ltr" class="mw-content-ltr">It seems that the ‘sensitization’ of the trigeminal nociception system, the facilitation effect on the mandibular reflesxs, and the hyper-excitability of CNS are neurophysiopathogenetic phenomena that are related to pain in the craniofacial district</span>. <span lang="en" dir="ltr" class="mw-content-ltr">At the same time, the recovery cycle of the torpedo period shows the level of neuronal excitability of the trigeminal system, and it could be a valid method of testing the excitability of the nervous system</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">The recovery cycle of the masseteric reflection reflex</span> (<sub>rc</sub> MIR: recovery cycle Masseteric Inhibitory Reflex) <span lang="en" dir="ltr" class="mw-content-ltr">has been studied by generating pairs of stimuli with identical characteristics provided percutaneously by an electrical stimulator positioned on the patient’s face in the emergency area of the mental nerves</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 8).

<span lang="en" dir="ltr" class="mw-content-ltr">Stimulation was carried out with a square-wave electrical stimulation that was 2.5 times the inhibitory reflection threshold, which was able to evoke a distinct <sub>rc</sub> MIR, composed of the two silent periods called ‘exteroceptive suppression’ to distinguish them from separate mechanical Silent Periods (SPs)</span>; <span lang="en" dir="ltr" class="mw-content-ltr">these can be recognized in a first silent period called ES</span><sub>1</sub> (<span lang="en" dir="ltr" class="mw-content-ltr">Exteroceptive Suppression</span> <sub>1</sub>) <span lang="en" dir="ltr" class="mw-content-ltr">and a second silent period named ES</span><sub>2</sub> (<span lang="en" dir="ltr" class="mw-content-ltr">Exteroceptive Suppression</span> <sub>2</sub>) <span lang="en" dir="ltr" class="mw-content-ltr">interspersed by the resumption of the activity EMG</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Interposed IA Activity</span>). <span lang="en" dir="ltr" class="mw-content-ltr">The first stimulus (S1) is considered to be conditioning and the second (S2) a stimulation test</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The interstimulus range to verify the presence of a neural hyperexcitability between S1 and S2 has been set at 150 ms</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">In our studies, healthy subjects were instructed to tighten their teeth to produce the maximum EMG activity and maintain it for at least 3 seconds with the help of visual and sound feedback</span>. <span lang="en" dir="ltr" class="mw-content-ltr">After 60 seconds of rest, the subject repeated the contraction</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The EMG signal was recorded both in direct mode and in mediated mode</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The disposition of the recorder electrodes must be the same as for the registration of the <sub>b</sub> Root, jaw jerk, and SP</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The parameters of the preamplifier will have to be set in 50 ms per division, 100 mV per division, and the filter bandwidth of 50 Hz–1 kHz</span>.
[[File:Laser test.jpg|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 9:''' <span lang="en" dir="ltr" class="mw-content-ltr">Preparation of the subject to laser stimulation to evoke nociceptive evoked potentials and masseteric inhibitory reflexes</span>.]]

====<span lang="en" dir="ltr" class="mw-content-ltr">Laser Evoked Potentials and Masseteric Laser Silent Period</span>====

<span lang="en" dir="ltr" class="mw-content-ltr">To evoke motor responses from the masticatory muscles or potential laser evenings, we employ a laser stimulator</span> CO<sub>2</sub> (Neurolas, <span lang="en" dir="ltr" class="mw-content-ltr">Florence, Italy</span>) <span lang="en" dir="ltr" class="mw-content-ltr">capable of generating a radiant caloria (10.6 mm; intensity 1.5–15 W; duration of 10–15 ms; diameter of the 2.5 mm spot) in the area of the skin in upper and lower upper and lower region (trigeminal terrain V2 and V3)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The subjects must sit comfortably in the dental chair and wear protective goggles</span> (<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 9). <span lang="en" dir="ltr" class="mw-content-ltr">To avoid the habit to the nociceptive stimuli and the overheating of the skin, the irradiated points have been shifted after each stimulation</span>.  

[[File:Laser_Evoked_Potentials_-_Blink_reflex_-_Masseter_Silent_Period.jpg|left|thumb|'''<span lang="en" dir="ltr" class="mw-content-ltr">Figure</span> 10:'''  <span lang="en" dir="ltr" class="mw-content-ltr">Laser stimulation that evoke a Blink reflex (BR), a Masseter Inhibitor Reflex (MIR) and Evoked Potentials Laser</span> (LEPs)]]
<span lang="en" dir="ltr" class="mw-content-ltr">The perception threshold has been determined by the limits method in two sets of intensity by increasing or decreasing the trigger stimulation</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The intensity of the laser beam is fixed at 1.5 the perceptual threshold</span>. <span lang="en" dir="ltr" class="mw-content-ltr">With regard to LEP (LEP: Laser Evoked Potentials), signals are recorded through the top-disk electrodes (Cz) with two references for each side on the ear lobes</span> (A1, A2). <span lang="en" dir="ltr" class="mw-content-ltr">Two blocks of eight to 12 tests each are mediated off-line. Signs are amplified, filtered (0.5–50 Hz), and stored by means of an analyser for biopotential</span> (Premiere, Medelec, UK). <span lang="en" dir="ltr" class="mw-content-ltr">For each block, we have measured the latency of the N and P components and the peak-to-peak width of the potential evoked</span>.<ref>{{cita libro 
 | autore = Romaniello A
 | autore2 = Cruccu G 
 | autore3 = Frisardi G
 | autore4 = Arendt-Nielsen L
 | autore5 = Svensson P
 | titolo = Assessment of nociceptive trigeminal pathways by laser-evoked potentials and laser silent periods in patients with painful temporomandibular disorders
 | url = https://pubmed.ncbi.nlm.nih.gov/12749956/
 | volume = 
 | opera = Pain
 | anno = 2003
 | editore = 
 | città = 
 | ISBN = 
 | DOI = 10.1016/s0304-3959(02)00347-0
 | oaf = <!-- qualsiasi valore -->
 | LCCN = 
 | OCLC = 
 | PMID = 12749956
 }}</ref> 

<span lang="en" dir="ltr" class="mw-content-ltr">For LSPs, the same parameters were used as described above, but the recording is performed on masseter muscles</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The area was subtracted from the 100-ms curve prior to adjusted and mediated laser stimulus (pre-analysis)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The duration of the registered EMG activity is 400 ms, of which 100 ms corresponds to pre-stimulus and 300 ms in the post-stimulus period</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The EMG signals are amplified, filtered (20 Hz–1 kHz), and sampled at 4 kHz</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Subjects are asked to tighten their teeth with the maximum muscular strength to determine the EMG activity corresponding to the Maximum Volunteer Contraction</span> (MVC: <span lang="en" dir="ltr" class="mw-content-ltr">Maximum Voluntary Contraction</span>) <span lang="en" dir="ltr" class="mw-content-ltr">of masseter muscles and at different levels (15–25%), (35–45%), (55-65%), and (75–85%) of MVC</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Subjects receive visual feedback with markers on the computer screen, which clearly indicates when the default level is reached</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">As Figure 10 shows, the results of the following work are schematized in accordance with the type of test performed</span>. <span lang="en" dir="ltr" class="mw-content-ltr">With a laser stimulation in the skin region corresponding to the emergence of the supraorbital nerve (V1), we can have a Blink Reflex as a reflected response (BR) and notice the perfect symmetry of the responses on sides R1 and R2</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Stimulation in the perioral region will result in a reflex response from the masseterini muscles called Laser Silent Period</span> (LSP: <span lang="en" dir="ltr" class="mw-content-ltr">Laser Silent Period</span>). <span lang="en" dir="ltr" class="mw-content-ltr">We might note, in this test, a slight asymmetry of the track, mainly caused by the different degree of motoneural recruitment in the maximum intercuspidation</span>. <span lang="en" dir="ltr" class="mw-content-ltr">The registration on the scalp determines the potential laser summers of the trigeminal somatosensory area (LEPs) and measure the negative and positive spikes (N and P)</span>. <span lang="en" dir="ltr" class="mw-content-ltr">Here too, we witness a high level of symmetry</span>. 

<span lang="en" dir="ltr" class="mw-content-ltr">The Exposed Laser procedure is very interesting because — as shown in Figure 19 — there is evidence of a high symmetry of the blue component of the Blink reflex (R2 right and left) that corresponds to the motor nerve activity of the facial nerve</span>; <span lang="en" dir="ltr" class="mw-content-ltr">a relative somatosensory symmetry might be detected (N2 and P2, while a clear asymmetry of the MCV masseterin (MIR) is denoted in the width of the motor unit by both stimulus and post-inhibition</span>. <span lang="en" dir="ltr" class="mw-content-ltr">This introduces an important concept of the neural symmetry that might reveal an extraordinarily fascinating world of neurophysiopathological notions in the field of mastication</span>.


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[[Category:Source Chapter]]
[[Category:Articles about trigeminal nervous system]]