The mesencephalic nucleus of trigeminal nerve is involved with reflex proprioception of the

periodontium The periodontium is the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms περί ''peri''-, meaning "around" and -''odont'', meaning "tooth". ...

and of the

muscles of mastication There are four classical muscles of mastication. During mastication, three muscles of mastication (''musculi masticatorii'') are responsible for adduction of the jaw, and one (the lateral pterygoid) helps to abduct it. All four move the jaw late ...

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 Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

, 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 The sensory trigeminal nerve nuclei are the largest of the cranial nerve nuclei, and extend through the whole of the midbrain, pons and medulla, and into the high cervical spinal cord. The nucleus is divided into three parts, from rostral to caud ...

, three sensory and one motor. The other two sensory nuclei are the

chief sensory nucleus The principal sensory nucleus of trigeminal nerve (or chief sensory nucleus of V, main trigeminal sensory nucleus) is a group of second-order neurons which have cell bodies in the caudal pons. It receives information about discriminative sensation ...

mediating conscious facial touch and the

spinal trigeminal nucleus The spinal trigeminal nucleus is a nucleus in the medulla that receives information about deep/crude touch, pain, and temperature from the ipsilateral face. In addition to the trigeminal nerve (CN V), the facial (CN VII), glossopharyngeal (CN IX), ...

, mediating

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

and temperature in the head, and is of importance in

headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

. The

trigeminal motor nucleus The trigeminal motor nucleus contains motor neurons that innervate muscles of the first branchial arch, namely the muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric. This nucleus is l ...

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 central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

(CNS), the mesencephalic nucleus contains no chemical

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

s but are electrically coupled. Neurons of this nucleus are pseudounipolar that receive proprioceptive information from the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

and send projections to the

to mediate monosynaptic

jaw jerk reflex The jaw jerk reflex or the masseter reflex is a stretch reflex used to test the status of a patient's trigeminal nerve ( cranial nerve V) and to help distinguish an upper cervical cord compression from lesions that are above the foramen magnum. The ...

es. 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 The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

, making it neuroanatomically unique .

Development

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.

Clinical significance

Clinically, because of its reflex function, the mesencephalic nucleus can be tested with the

. 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.

References

External links

Washington University
{{Authority control Cranial nerve nuclei Trigeminal nerve Proprioception

Development

Clinical significance

See also

References

External links