CN III, IV, VI

CN III, IV, VIOculomotor nerve. Trochlear nerve. Abducens nerve
~ 7 min

In this note, we are going to discuss the anatomy and function of the oculomotor nerve (CN III), the trochlear nerve (CN IV), and the abducens nerve (CN VI). These cranial nerves control our eye movements.

Oculomotor nerve

The oculomotor nerve (n. oculomotorius) is the cranial nerve III.

Oculomotor nerve (n. oculomotorius)
Oculomotor nerve (n. oculomotorius)
Oculomotor nerve (n. oculomotorius)
Oculomotor nerve (n. oculomotorius)

According to the generally accepted classification of functional components, it contains general somatic efferent fibers (GSE) and general visceral efferent fibers (GVE). That means that it is a motor nerve.

The somatic efferent fibers arise from the oculomotor nucleus (nucleus nervi oculomotorii), which is located in the midbrain at the level of the superior colliculi.

Oculomotor nucleus (nucleus nervi oculomotorii)
Oculomotor nucleus (nucleus nervi oculomotorii)
Oculomotor nucleus (nucleus nervi oculomotorii)
Oculomotor nucleus (nucleus nervi oculomotorii)
Oculomotor nucleus (nucleus nervi oculomotorii)
Oculomotor nucleus (nucleus nervi oculomotorii)

The nucleus lies within the periaqueductal gray matter surrounding the cerebral aqueduct.

Cerebral aqueduct (aqueductus cerebri)
Cerebral aqueduct (aqueductus cerebri)

It consists of separate groups of cells, each of which is a source of fibers for the innervation of a certain extraocular muscle.

The visceral efferent fibers arise from the accessory oculomotor nucleus, also known as the Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii), which is a parasympathetic nucleus. It is located nearby.

Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)
Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)
Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)
Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)
Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)
Accessory oculomotor nucleus | Edinger-Westphal nucleus (nucleus accessorius nervi oculomotorii)

Both the somatic and visceral efferent fibers exit the anterior surface of the brainstem as the oculomotor nerve.

Oculomotor nerve (n. oculomotorius)
Oculomotor nerve (n. oculomotorius)

Then it pierces the dura mater and runs through the roof and lateral wall of the cavernous sinus (sinus cavernosus).

Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (n. oculomotorius)
Cavernous sinus (n. oculomotorius)

Next, the oculomotor nerve enters the orbit through the superior orbital fissure (fissura orbitalis superior).

Superior orbital fissure (fissura orbitalis superior)
Superior orbital fissure (fissura orbitalis superior)
Oculomotor nerve (n. oculomotorius)
Oculomotor nerve (n. oculomotorius)

At this point, it divides into superior and inferior branches (ramus superior et ramus inferior).

Superior brunch (ramus superior)
Superior brunch (ramus superior)
Inferior brunch (ramus inferior)
Inferior brunch (ramus inferior)

The superior branch innervates the superior rectus muscle (m. rectus superior),

Superior rectus muscle (m. rectus superior)
Superior rectus muscle (m. rectus superior)
Superior rectus muscle (m. rectus superior)
Superior rectus muscle (m. rectus superior)

pierces it and innervates the levator palpebrae superioris muscle (m. levator palpebrae superioris).

Levator palpebrae superioris muscle (m. levator palpebrae superioris)
Levator palpebrae superioris muscle (m. levator palpebrae superioris)
Levator palpebrae superioris muscle (m. levator palpebrae superioris)
 Levator palpebrae superioris muscle (m. levator palpebrae superioris)

The inferior branch innervates the medial rectus muscle (m. rectus medialis)

Medial rectus muscle (m. rectus medialis)
Medial rectus muscle (m. rectus medialis)
Medial rectus muscle (m. rectus medialis)
Medial rectus muscle (m. rectus medialis)

and inferior rectus muscle (m. rectus inferior),

Inferior rectus muscle (m. rectus inferior)
Inferior rectus muscle (m. rectus inferior)
Inferior rectus muscle (m. rectus inferior)
Inferior rectus muscle (m. rectus inferior)

as well as the inferior oblique muscle (m. obliquus inferior).

Inferior oblique muscle (m. obliquus inferior)
Inferior oblique muscle (m. obliquus inferior)
Inferior oblique muscle (m. obliquus inferior)
Inferior oblique muscle (m. obliquus inferior)

This helps us to direct our gaze superiorly, inferiorly, and medially.

The inferior branch of the oculomotor nerve also carries visceral efferent fibers to the ciliary ganglion (ganglion ciliare).

Ciliary ganglion (ganglion ciliare)
Ciliary ganglion (ganglion ciliare)
Ciliary ganglion (ganglion ciliare)
Ciliary ganglion (ganglion ciliare)

Postsynaptic fibers from the ciliary ganglion pass to the eyeball in the short ciliary nerves (nn. ciliares breves) to innervate the intrinsic muscles of the eye.

Short ciliary nerves (nn. ciliares breves)
Short ciliary nerves (nn. ciliares breves)
Short ciliary nerves (nn. ciliares breves)
Short ciliary nerves (nn. ciliares breves)

In particular, the sphincter pupillae (m. sphincter pupillae), which causes constriction of the pupil,

Sphincter pupillae (m. sphincter pupillae)
Sphincter pupillae (m. sphincter pupillae)

and the ciliary muscle (m. ciliaris),

Ciliary muscle (m. ciliaris)
Ciliary muscle (m. ciliaris)

Trochlear nerve

The trochlear nerve (n. trochlearis) is the cranial nerve IV.

Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)

According to the generally accepted classification of functional components, it contains general somatic efferent fibers (GSE). That means that it is a motor nerve.

It arises from the trochlear nucleus (nucleus nervi trochlearis), located within the periaqueductal gray matter of the midbrain, at the level of the inferior colliculi.

Trochlear nucleus (nucleus nervi trochlearis)
Trochlear nucleus (nucleus nervi trochlearis)
Trochlear nucleus (nucleus nervi trochlearis)
Trochlear nucleus (nucleus nervi trochlearis)
Inferior colliculus (colliculus inferior)
Inferior colliculus (colliculus inferior)

Then it emerges from the posterior surface of the midbrain, crosses the midline, and passes anteriorly around the contralateral side of the brainstem.

Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)

The trochlear nerve pierces the dura mater and passes anteriorly in the lateral wall of the cavernous sinus.

Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)

It enters the orbit through the superior orbital fissure (fissura orbitalis superior).

Superior orbital fissure (fissura orbitalis superior)
Superior orbital fissure (fissura orbitalis superior)
Trochlear nerve (n. trochlearis)
Trochlear nerve (n. trochlearis)

The trochlear nerve innervates the superior oblique muscle (m. obliquus superior), which abducts, depresses, and medially rotates the eye.

Superior oblique muscle (m. obliquus superior)
Superior oblique muscle (m. obliquus superior)
Superior oblique muscle (m. obliquus superior)
Superior oblique muscle (m. obliquus superior)

Abducens nerve

And finally, the abducens nerve (n. abducens), or cranial nerve VI.

Abducens nerve (n. abducens)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)

According to the generally accepted classification of functional components, it contains general somatic efferent fibers (GSE). That means that it is a motor nerve.

It arises from the abducens nucleus (nucleus nervi abducentis), which is located in the dorsal part of the pons.

Abducens nucleus (nucleus nervi abducentis)
Abducens nucleus (nucleus nervi abducentis)

The nerve emerges from the brainstem in the sulcus between the pons and the medulla oblongata.

Abducens nerve (colliculus facialis)
Abducens nerve (colliculus facialis)

The abducens nerve pierces the dura mater and runs through the cavernous sinus.

Cavernous sinus (n. abducens)
Cavernous sinus (n. abducens)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Cavernous sinus (sinus cavernosus)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)

It enters the orbit through the superior orbital fissure (fissura orbitalis superior),

Superior orbital fissure (fissura orbitalis superior)
Superior orbital fissure (fissura orbitalis superior)
Abducens nerve (n. abducens)
Abducens nerve (n. abducens)

and innervates the lateral rectus muscle (m. rectus lateralis), which abducts the eye to direct the pupil away from the nose.

Lateral rectus muscle (m. rectus lateralis)
Lateral rectus muscle (m. rectus lateralis)
Lateral rectus muscle (m. rectus lateralis)
Lateral rectus muscle (m. rectus lateralis)
Dictionary

CN III, IV, VI

Oculomotor nerve
n. oculomotorius
Nucleus of the oculomotor nerve
nucleus nervi oculomotorii
Cerebral aqueduct
aqueductus cerebri
Accessory nucleus of the oculomotor nerve
nucleus accessorius nervi oculomotorii
Sulcus of the oculomotor nerve
sulcus nervi oculomotrii
Cavernous sinus
sinus cavernosus
Superior orbital fissure
fissura orbitalis superior
Superior branch
ramus superior
Inferior branch
ramus inferior
Superior rectus muscle
m. rectus superior
Levator palpebrae superioris muscle
m. levator palpebrae superioris
Medial rectus muscle
m. rectus medialis
Inferior rectus muscle
m. rectus inferior
Inferior oblique muscle
m. obliquus inferior
Ciliary ganglion
ganglion ciliare
Short ciliary nerves
nn. ciliares breves
Sphincter pupillae muscle
m. sphincter pupillae
Ciliary muscle
m. ciliaris
Trochlear nerve
n. trochlearis
Nucleus of the trochlear nerve
nucleus nervi trochlearis
Inferior colliculus
colliculus inferior
Superior oblique muscle
m. obliquus superior
Abducens nerve
n. abducens
Nucleus of the abducens nerve
nucleus nervi abducentis
Facial colliculus
colliculus facialis
Lateral rectus muscle
m. rectus lateralis
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