1 Answers
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 joint receptors 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 , 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.