Anatomy and Microanatomy
- The MNTN is located in the brainstem, near the periaqueductal gray and lateral to the cerebral aqueduct.
- It is the only structure in the central nervous system to contain the cell bodies of first-order sensory neurons.
- The mesencephalic nucleus contains no chemical synapses but is electrically coupled.
- Neurons in this nucleus are pseudounipolar and receive proprioceptive afferent information from the mandible.
- They send efferent projections to the trigeminal motor nucleus to mediate monosynaptic jaw jerk reflexes.

Development
- The pseudounipolar neurons in the mesencephalic nucleus are embryologically derived from the neural crest.
- Instead of joining the trigeminal ganglion, the neurons migrate into the brainstem.
- The MNTN is believed to represent a primary sensory ganglion that becomes incorporated into the brainstem during embryologic development.

Function
- The MNTN is involved in reflex proprioception of the periodontium and the muscles of mastication in the jaw.
- Mechanoreceptive nerves in the periodontal ligament sense tooth movement and project to the mesencephalic nucleus.
- Afferent fibers from muscle spindles, the sensory organs of skeletal muscle, are stimulated by the stretch of jaw muscles.
- The mesencephalic nucleus is one of four trigeminal nerve nuclei, involved in conscious facial touch and pain/temperature perception.
- The trigeminal motor nucleus innervates the muscles of mastication and other associated muscles.

Clinical significance
- The mesencephalic nucleus can be tested with the jaw jerk reflex to assess its function.
- Lesions of the trigeminal mesencephalic nucleus can affect feeding due to its role in oral proprioception.
- The mesencephalic nucleus helps prevent excessive biting that may damage the dentition.

Unique features
- The mesencephalic nucleus can be considered functionally as a primary sensory ganglion embedded within the brainstem, making it neuroanatomically unique.