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Temporomandibular Joint (TMJ) Dysfunction
and
Emotional Stress
Physiological effects of emotional stress on the body and its effects on the TMJ
Effects on the nervous system
Most of the researches agree on the following neuronal network that controls mastication: cortico-bulbar inputs to contralateral brainstem structures first activate a relay in the medial pontomedullary reticular formation that eventually reaches the trigeminal motor nuclei and activates jaw opening or closing muscles. (Lavigne, Kato, Kolta, & Sessle, 2003)
The neurological mechanism underlying the control of the masticatory muscles is somewhat similar to brainstem control of the breathing patterns. Masticatory central pattern generator (CPG) consists of two groups of brain centres: rhythm generator that sets up the basic rhythm of mastication and burst generator that modulates the rhythm according to sensory inputs from oral cavity so that the movement becomes appropriate for the size of bolus, viscosity and temperature.(Lund, 1991)
Using MRI and PET scans it was shown the following areas are active during mastication: cortical primary somatosensory area, supplementary motor area, insula, cerebellum, and striatum of basal ganglia. (Momose et al., 1997)
In addition to the above structures, other cerebral structures are associated with generation of jaw movements include the lateral hypothalamus, the anterior-lateral or central nuclei area of amygdala, thalamic reticular nuclei, the mesencephalic reticular formation, the pontine pyramidal tract, and red nuclei. The involvement of the above structures in the emotional responses has also been demonstrated in the various brain mapping studies.(Barrett et al., 2007) It can be hypothesised that activation of these structures during a strong emotional experience can activate jaw closing mechanisms as well.
In various animal studies it has been demonstrated that stimulation of hypothalamic ‘defence attack area’ facilitates jaw-closing muscle reflex, which indicates the trigeminal system is activated in aggressive behaviour. Also, it has been shown that central amygdaloid nuclei project to the contralateral trigeminal motor nuclei, the supratrigeminal area, and the pontine reticular formation. This supports interaction among aggressive behaviour, trigeminal sensorimotor functions and autonomic activities.(Lavigne et al., 2003)
Another research has shown that chronic stress causes greater subjective distress in acute stressful situation. It has also demonstrated increased levels of epinephrine and lower peak levels of β-endorphin during stressful event .(Pike et al., 1997) This way the increased sympathetic outflow via irritated trigeminal nerve can further exacerbate the symptoms of TMD, while the decrease of β-endorphin levels can increase the perceived pain.
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