| 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".) | |
| Details | |
| Identifiers | |
| Latin | nucleus mesencephalicus nervi trigemini |
| NeuroNames | 558 |
| NeuroLex ID | birnlex_1010 |
| TA98 | A14.1.05.409 |
| TA2 | 5887 |
| FMA | 54568 |
| Anatomical terms of neuroanatomy | |
Themesencephalic nucleus of trigeminal nerve is one of the sensory nuclei of thetrigeminal nerve (cranial nerve V). It is located in thebrainstem. It receivesproprioceptive sensory information from themuscles of mastication and other muscles of the head and neck. It is involved in processing information about the position of the jaw/teeth. It is functionally responsible for preventing excessive biting that may damage the dentition, regulating tooth pain perception, and mediating thejaw jerk reflex (by means of projecting to themotor nucleus of the trigeminal nerve).[1]
The axons of the neuron cell bodies of this nucleus provide sensory innervation to target tissues directly, whereas other sensory nuclei of the trigeminal nerve receive their sensory inputs by synapsing withprimary sensory neurons in thetrigeminal ganglion.[1]
The MNTN is located in thebrainstem, more specifically (sources vary) spanning the length of the midbrain[2]/in the caudal midbrain and rostral pons.[1] It is situated (sources vary) near[1]/within[2] theperiaqueductal gray, lateral to thecerebral aqueduct.[2]
The mesencephalic nucleus is the only structure in the central nervous system to contain the cell bodies of first order sensory neurons.[2] The mesencephalic nucleus can thus be considered functionally as a primarysensory ganglion embedded within thebrainstem,[1] making it neuroanatomically unique.[3]
Unlike many nuclei within thecentral nervous system (CNS), the mesencephalic nucleus contains no chemicalsynapses, neurons instead being electrically coupled.[4] Neurons of this nucleus arepseudounipolar, receivingproprioceptive afferent information from themandible and sending efferent projections to thetrigeminal motor nucleus to mediate the monosynapticjaw jerk reflex.[5]
The pseudounipolar neurons in the mesencephalic nucleus are embryologically derived from theneural crest. However, instead of joining the trigeminal ganglion, the neurons migrate into the brainstem.[6][7] The MNTN neurons directly receive sensory information, akin to neurons in the dorsal root ganglia.
The MNTN is involved in reflexproprioception of theperiodontium[8] and of themuscles of mastication in the jaw[9] 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 frommuscle spindles, the sensory organs ofskeletal muscle, are stimulated by the stretch of hard contraction of jaw muscles. Thetemporomandibular joint receptors and theGolgi tendon organs of the jaw muscles do not project to the mesencephalic nucleus.[10] The mesencephalic nucleus is one of fourtrigeminal nerve nuclei, three sensory and one motor. The other two sensory nuclei are thechief sensory nucleus mediating conscious facial touch and thespinal trigeminal nucleus, mediatingpain and temperature in the head, and is of importance inheadache. Thetrigeminal motor nucleus innervates the muscles of mastication,mylohyoid,anterior belly of digastric,tensor veli palatini, andtensor tympani.
Clinically, because of its reflex function, the mesencephalic nucleus can be tested with thejaw jerk reflex. Because of its function in oral proprioception, lesions of the trigeminal mesencephalic nucleus cause effects on feeding.[11] 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 containinge.g. bone, cherry seeds, apricot stonesetc.
