supranuclear

Supranuclear is an anatomical and clinical term used to describe neural structures or control mechanisms located above the nuclei of motor neurons. The prefix supra- means above, and nucleus refers to a cellular or neural nucleus. In neurology, supranuclear control denotes pathways that influence motor neurons indirectly, via higher brain centers, in contrast to infranuclear or nuclear control that arises from the cranial nerve nuclei themselves.

In the context of eye movement, supranuclear pathways originate in cortical and brainstem oculomotor networks that coordinate voluntary gaze. Damage to these supranuclear pathways causes supranuclear gaze palsies, in which the patient cannot voluntarily move the eyes in certain directions, while reflex movements mediated by the oculomotor nerves may be spared early on.

Progressive supranuclear palsy (PSP) is a prototypical neurodegenerative condition in which supranuclear control of eye movements, balance, posture, and speech are progressively impaired. A hallmark feature is vertical supranuclear gaze palsy, especially with loss of upward gaze, alongside axial rigidity and postural instability. The underlying pathology involves degeneration in the midbrain, basal ganglia, and other brain regions rather than a single cranial nerve nucleus.

Outside ophthalmology, supranuclear is used more generally to describe any control or processing that is situated above a defined nucleus in the central nervous system, but the term is most often encountered in discussions of eye movements and related motor control.