mesencephalic

Mesencephalic is an anatomical term referring to the mesencephalon, the midbrain portion of the brainstem. The mesencephalon lies between the diencephalon (forebrain) and the pons and develops from the middle primary brain vesicle. The word derives from Greek, with mesos meaning middle and enkephalon meaning brain.

Anatomy and structure: The mesencephalon comprises the tectum and the tegmentum, with the ventral surface containing the cerebral peduncles. The tectum includes the superior and inferior colliculi, involved in visual and auditory processing, respectively. The tegmentum houses several important structures, including the red nucleus, the substantia nigra, and the nuclei of cranial nerves III (oculomotor) and IV (trochlear). The periaqueductal gray surrounds the cerebral aqueduct. The mesencephalon also contains the mesencephalic nucleus of the trigeminal nerve, a unique primary sensory nucleus for proprioception of the jaw and facial muscles.

Development: Embryologically, the mesencephalon is one of the three primary brain vesicles and remains a distinct region as development proceeds, unlike the forebrain and hindbrain, which undergo further regional subdivision.

Function: The midbrain participates in motor control, sensorimotor integration, and reflexive responses. The substantia nigra’s dopaminergic neurons are essential for movement regulation and are implicated in Parkinson disease. The tectum and tegmentum contribute to visual and auditory processing, gaze stabilization, and eye movements via the oculomotor and trochlear systems. The mesencephalic nucleus of V provides proprioceptive information for jaw movements and is notable for containing neurons within the central nervous system.

See also: midbrain, mesencephalon, brainstem.