Cranial Nerve 3 – Oculomotor Nerve

@   GSE、GVE

@   Oculomotor Nuclear Complex

1.     Lateral somatic cell columns (GSE)

(1)  Dorsal cell nucleus Þ 支配Inferior rectus muscle。

(2)  Intermediate cell column Þ 支配Inferior oblique muscle。

(3)  Ventral cell column Þ 支配Medial rectus muscle。

(4)  Medial cell column Þ 支配Superior rectus muscle。(Root fibers cross)

2.     Caudal central nucleus (GSE) Þ 位於Nuclear complex的Caudal 1/3，支配Levator palpebrae superioris muscle。(Root fibers cross and uncross)

3.     Dorsal visceral nuclei (GVE) Þ 為Edinger-Westphal nucleus and anterior median nuclei，其神經元發出的纖維終止於 Ciliary ganglion，去支配 Sphincter pupillae muscle of iris 與 Ciliary muscle。

4.     Central nucleus of Perlia Þ 存在與否未知，功能上可能跟Convergence有關。

@   Afferent Connections of the Oculomotor Nuclear Complex

1.     Direct：Cerebral cortex、Cerebellum、Medial and superior vestibular nuclei、Inferior and lateral vestibular nuclei、Interstitial nucleus of Cajal、Abducens internuclear neurons、Nucleus prepositus hypoglossi (NPH)、Rostral interstitial nucleus of MLF (RiMLF)、Pretectal olivary nucleus。

2.     Indirect：Corticobulbar fibers。

@   Pupillary Reflexes (2進3出) Þ Light shone on the retina of one eye causes both pupils to constrict.

1.     Direct pupillary light reflex

2.     Consensual pupillary light reflex Þ Section of the posterior commissure reduces but does not abolish this reflex. (See the following reasons─pathway)

※    Pathway：Light Þ Retina Þ Optic nerve Þ Optic chiasm Þ Optic tract Þ Brachium of the superior colliculus Þ Pretectal olivary nucleus Þ Some axons of pretectal neurons cross in the posterior commissure Þ Terminate in the bilateral visceral nuclei of the oculomotor nuclear complex Þ Sphincter pupillae muscle of the iris Þ Pupillary constriction

※ 損傷中樞的Oculomotor efferent pathway會造成Anisocoria (瞳孔大小不等)。

@   Accommodation-Convergence Reaction Þ It occurs when gaze is shifted from a distant object to a near one (看近物). This reaction involves：

1.     Contraction of both medial rectus muscles for convergence

2.     Contraction of both ciliary muscle which relaxes the suspensory ligament of the lens and causes the lens to assume a more convex shape

3.     Pupillary constriction

※ Pathway：Retinal impulses Þ Visual cortex Þ Superior colliculus and pretectal region Þ Direct or indirect to the oculomotor nuclear complex

@   Lesions of Oculomotor Nerve

1.     Complete lesion

(1)  Ipsilateral complete ptosis (drooping) of the eyelid (垂瞼)

(2)  External (Lateral) strabismus (外斜視)

(3)  Mydriasis (散瞳)

(4)  A loss of the pupillary light reflex and convergence

(5)  A loss of lens accommodation

2.     Superior alternating hemiplegia (= Weber’s syndrome) Þ Lesions involving the oculomotor nerve and corticospinal fibers in the ventral midbrain

(1)  An ipsilateral oculomotor paralysis

(2)  A contralateral hemiplegia (especially the lower face and tongue)

@   Argyll-Robertson Pupil Þ 由Syphilis (Tabes dorsalis) (梅毒、脊髓癆)所造成。

1.     Miosis (縮瞳)

2.     No reaction to light

3.     Without affecting accommodation

@   Horner’s Syndrome Þ Interruption of descending autonomic pathways from the hypothalamus to the reticular formation which are relayed to upper thoracic spinal segments。

1.     Miosis

2.     Pseudoptosis (假性垂瞼)

3.     Apparent enophthalmos (眼球陷沒) Þ Orbital muscle of Müller可使眼球在眼眶內維持向前凸出，當SCG發出的Sympathetic nerve受影響時，就會造成眼球陷沒。

4.     Vasodilation and dryness of the skin over the face

@   Oculomotor Nerve in the PNS

1.     Superior division

(1)  To levator palpebrae superioris m.

(2)  To superior rectus m.

2.     Inferior division

(1)  Motor root to ciliary ganglion (parasympathetic nerve fibers)

(2)  To medial rectus m.

(3)  To inferior rectus m.

(4)  To inferior oblique m.

@   Functional Components of the Oculomotor Nerve

1.     GSE － To the above-mentioned extrinsic ocular muscles and the lavetor palpebrae superioris muscle

2.     GSA (possible) － Proprioceptive fibers from the above-mentioned extrinsic ocular muscles ® Communicating branch (in the cavernous sinus) with the trigeminal nerve ® Mesencephalic nucleus

3.     GVE － Edinger-Westphal nucleus and anterior median nuclei ® Oculomotor nerve ® Parasympathetic root ® Ciliary ganglion ® Short ciliary nerve ® Ciliary and Sphincter pupillae muscles of the iris