Point 21
Intro
Point: 21. Oculomotor nuclear complex (C.N. III)
Function:
Some cells in this complex possess axons that innervate
extraocular eye muscles (also levator palpebrae) except for
lateral rectus and superior oblique. Other cells are
preganglionic parasympathetic that possess axons which
synapse in the ciliary ganglion and are involved in
constricting the pupil.
Pathway:
All axons (both somatic and autonomic) pass ventrally to
exit the midbrain between the cerebral peduncles
(interpeduncular fossa). Somatic fibers directly innervate
eye muscles and levator palpebrae, while preganglionic
parasympathetic axons synapse within the ciliary ganglion.
Short postganglionic parasympathetic fibers then pass to the
sphincter pupillae (constrict pupil) of the iris and the
ciliary muscles.
Deficits:
Lesion of the oculomotor complex or its nerve fibers results
in atrophy of all muscles innervated, diplopia due to an
outward and slightly downward rotation of the eye (you must
raise the eyelid to see this), ptosis (levator) and a
DILATED PUPIL. ALL PROBLEMS ARE IPSI.
Other Note:
Parasympathetic fibers (lesion=dilated pupil) can be damaged
without somatic fiber involvement. C.N. III is stretched
upon herniation of IPSI. uncus and adjacent temporal lobe.
Corticospinal fibers in the opposite (CONTRA.) cerebral
peduncle are damaged too! Thus dilated pupil and hemiplegia
are on SAME side (corticospinal fibers CROSS in the pyr.
dec.).