Nerve
Oculomotor nerve (CN III)
Moves the eye and lifts the lid
High-yield
Palsy → 'down and out' eye, ptosis, and a dilated pupil (parasympathetic fibres run on the surface — compressed early by aneurysm/herniation).
Overview
The third cranial nerve, supplying four of the six extraocular muscles, the levator palpebrae, and (parasympathetically) pupil constriction and lens accommodation.
Reference facts
- Roots
Motor and parasympathetic (cranial nerve)
- Course
Emerges from the midbrain, passes through the cavernous sinus and superior orbital fissure into the orbit
- Motor
Superior, inferior, and medial recti; inferior oblique; levator palpebrae superioris; (parasympathetic) sphincter pupillae and ciliary muscle
- Sensory
None
Clinical correlation
A blown (fixed, dilated) pupil signals compressive CN III palsy from uncal herniation until proven otherwise.