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 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. 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 and temperature in the head, and is of importance in headache. The trigeminal motor nucleus innervates the muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani.
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 pseudounipolar that receive proprioceptive information from the mandible and send projections to the trigeminal motor nucleus to mediate monosynaptic jaw jerk reflexes.
The mesencephalic nucleus is the only structure in the central nervous system to contain the cell bodies of first order sensory neurons. The mesencephalic nucleus can thus be considered functionally as a sensory ganglion embedded within the brainstem, making it neuroanatomically unique.
The pseudounipolar neurons in the mesencephalic nucleus are embryologically derived from the neural crest. However, instead of joining the trigeminal ganglion, the neurons migrate into the brainstem.
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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