Mesencephalic nucleus of trigeminal nerve
|Mesencephalic nucleus of trigeminal nerve|
The cranial nerve nuclei schematically represented; dorsal view. Motor nuclei in red; sensory in blue. (Trigeminal nerve nuclei are at "V".)
|Latin||nucleus mesencephalicus nervi trigemini|
|Anatomical terms of neuroanatomy|
The mesencephalic nucleus 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. Likewise, afferent fibers from muscle spindles, the sensory organs of skeletal muscle, are stimulated by the stretch of hard contraction of jaw muscles. The temporomandibular joints and the Golgi tendon organs of the jaw muscles do not project to the mesencephalic nucleus. The mesencephalic nucleus is one of four trigeminal nerve nuclei, three sensory and one motor. The other two sensory nuclei are the chief sensory nucleus mediating conscious facial touch and the spinal trigeminal nucleus, mediating pain in the head, and is of importance in headache. The trigeminal motor nucleus innervates the muscles of mastication.
Unlike many nuclei within the central nervous system (CNS), the mesencephalic nucleus contains no chemical synapses but are electrically coupled. Neurons of this nucleus are unipolar cells that receive proprioceptive information from the mandible and send projections to the trigeminal motor nucleus to mediate monosynaptic jaw jerk reflexes. It is also the only structure in the CNS to contain first order sensory neurons, cell bodies of primary afferents in contact with the periphery, which are usually contained within ganglia (like the trigeminal ganglion). The mesencephalic nucleus can thus be considered functionally as a sensory ganglion embedded within the brainstem, making it neuroanatomically unique.
Clinically, because of its reflex function, the mesencephalic nucleus can be tested with the jaw jerk reflex. Because of its function in oral proprioception, lesions of the trigeminal mesencephalic nucleus cause effects on feeding. The mesencephalic nucleus can be thought of simply as the "nucleus that keeps your teeth in" by preventing one from biting down hard enough to lose a tooth on foods containing eg. bone, cherry seeds, apricot stones etc.
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- Yokoyama, S; Kinoshita, K; Muroi, Y; Ishii, T (2013). "The effects of bilateral lesions of the mesencephalic trigeminal sensory nucleus on nocturnal feeding and related behaviors in mice". Life Sciences. 93: 681–686. doi:10.1016/j.lfs.2013.09.015. PMID 24063988.