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It's seen that GSA (General Somatic Afferent) fibres (of CN V) have their cell bodies in trigeminal ganglion. But the proprioceptive fibres' peripheral processes terminate at mesencephalic trigeminal nucleus, making it the only nucleus in CNS where cell bodies of 1st order neurons are present.

Why this is so?

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  • $\begingroup$ if you are satisfied you may accept the answer for the future reference. $\endgroup$ – Ojasvi Oct 19 at 3:41
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The mesencephalic nucleus of trigeminal nerve is involved with reflex proprioception of the periodontium and of the muscles of mastication in the jaw that functions to prevent biting down hard enough to lose a tooth. To subserve this reflex protective function, mechanoreceptive nerves in the periodontal ligament sense tooth movement and project to the mesencephalic nucleus.

The functional significance of this anomaly is unclear, although there is a hint of special neural processing in the fact that, unlike DRGs and normal cranial nerve ganglia, MesV neurons receive synaptic input. Another hint is that while at spinal levels opposing extensor and flexor muscle blocks are roughly equal in size, in the orofacial motor system there is asymmetry. Jaw-closing muscles, the flexors, are massive and powerful with rich muscle spindle and Golgi tendon organ innervation. The jaw-opening muscles, the extensors, are small and delicate and lack muscle spindles and Golgi tendon organs

Reference

It is responsible for unconscious proprioception that stems from muscle spindles in the muscles of mastication and other muscles of the head and neck. It is thus essential in the process of receiving sensory information about tooth pain, helps prevent excessive biting that may break a tooth, receives information about stretch sensation from the muscles of mastication, and serves as the afferent limb of the jaw jerk reflex. Reference

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