The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a
cranial nerve
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
that enters the
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
through the
superior orbital fissure
The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens ne ...
and innervates
extraocular muscles
The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...
that enable most
movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the
intrinsic eye muscles
In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
that enable pupillary constriction and accommodation (ability to focus on near objects as in reading). The oculomotor nerve is derived from the
basal plate of the
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
nic
midbrain
The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness), and temperature regulation. The name comes from the Greek ''mesos'', ...
. Cranial nerves
IV and
VI also participate in control of
eye movement.
Structure
The oculomotor nerve originates from the third nerve
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
* Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucl ...
at the level of the
superior colliculus in the midbrain. The third nerve nucleus is located ventral to the
cerebral aqueduct, on the pre-aqueductal
grey matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is ...
. The fibers from the two third nerve nuclei located laterally on either side of the cerebral aqueduct then pass through the
red nucleus
The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. ...
. From the red nucleus fibers then pass via the
substantia nigra
The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts of the substantia nigra ap ...
to emerge from the substance of the brainstem at the oculomotor sulcus (a groove on the lateral wall of the
interpeduncular fossa).
On emerging from the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...
, the nerve is invested with a sheath of
pia mater, and enclosed in a prolongation from the
arachnoid. It passes between the
superior cerebellar (below) and
posterior cerebral
The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bif ...
arteries (above), and then pierces the dura mater anterior and lateral to the
posterior clinoid process, passing between the free and attached borders of the
tentorium cerebelli
The cerebellar tentorium or tentorium cerebelli ( Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.
Structure
The cerebellar tentorium is an arc ...
.
It traverses the
cavernous sinus, above the other orbital nerves receiving in its course one or two filaments from the
cavernous plexus of the sympathetic nervous system, and a communicating branch from the
ophthalmic division
The ophthalmic nerve (V1) is a sensory nerve of the face. It is one of three divisions of the trigeminal nerve (CN V). It has three branches that provide sensory innervation to the eye, the skin of the upper face, and the skin of the anterior ...
of the
trigeminal nerve. As the oculomotor nerve enters the orbit via the
superior orbital fissure
The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens ne ...
it then divides into a superior and an inferior branch.
Superior branch
The ''superior branch'' of the oculomotor nerve or the ''superior division'', the smaller, passes medially over the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
. It supplies the
superior rectus and
levator palpebrae superioris.
Inferior branch
The ''inferior branch'' of the oculomotor nerve or the ''inferior division'', the larger, divides into three branches.
* One passes beneath the optic nerve to the
medial rectus.
* Another, to the
inferior rectus.
* The third and longest runs forward between the inferior recti and lateralis to the
inferior oblique
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is one of the extraocular muscles, and is attached to the maxillary bone (origin) and ...
.
*From the third one, a short thick branch is given off to the lower part of the
ciliary ganglion, and forms its short root.
All these branches enter the muscles on their ocular surfaces, with the exception of the nerve to the inferior oblique, which enters the muscle at its posterior border.
Nuclei
The oculomotor nerve (CN III) arises from the anterior aspect of
mesencephalon (midbrain). There are two nuclei for the oculomotor nerve:
* The
oculomotor nucleus originates at the level of the
superior colliculus. The muscles it controls are the striated muscle in levator palpebrae superioris and other
extraocular muscles
The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...
except for the
superior oblique muscle and the
lateral rectus muscle.
* The
Edinger-Westphal nucleus supplies
parasympathetic
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...
fibers to the eye via the
ciliary ganglion, and thus controls the
sphincter pupillae muscle (affecting
pupil constriction) and the
ciliary muscle (affecting
accommodation).
Sympathetic postganglionic fibres also join the nerve from the plexus on the internal carotid artery in the wall of the cavernous sinus and are distributed through the nerve, e.g., to the smooth muscle of superior tarsal (Mueller's) muscle.
Function
The oculomotor nerve includes axons of type GSE,
general somatic efferent, which innervate skeletal muscle of the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. (Innervates all the extrinsic muscles except superior oblique and lateral rectus.)
The nerve also includes axons of type GVE,
general visceral efferent, which provide preganglionic parasympathetics to the ciliary ganglion. From the ciliary ganglion postganglionic fibers pass through the short ciliary nerve to the constrictor pupillae of the iris and the ciliary muscles.
Clinical significance
Disease
Paralysis of the oculomotor nerve, i.e.,
oculomotor nerve palsy, can arise due to:
*direct
trauma
Trauma most often refers to:
*Major trauma, in physical medicine, severe physical injury caused by an external source
*Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event
*Traumatic inju ...
,
*demyelinating diseases (e.g.,
multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This ...
),
*increased intracranial pressure (leading to
uncal herniation)
**due to a space-occupying lesion (e.g.,
brain cancer
A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and second ...
) or a
**spontaneous
subarachnoid haemorrhage (e.g.,
berry aneurysm
An intracranial aneurysm, also known as a brain aneurysm, is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel.
Aneurysms in the posterior circu ...
), and
*microvascular disease, e.g., diabetes.
In people with
diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
and older than 50 years of age, an oculomotor nerve palsy, in the classical sense, occurs with sparing (or preservation) of the pupillary reflex. This is thought to arise due to the anatomical arrangement of the
nerve fibers in the oculomotor nerve; fibers controlling the pupillary function are superficial and spared from
ischemic injuries typical of diabetes. On the converse, an aneurysm which leads to compression of the oculomotor nerve affects the superficial fibers and manifests as a third nerve palsy with loss of the pupillary reflex (in fact, this third nerve finding is considered to represent an aneurysm—until proven otherwise—and should be investigated).
Examination
Eye muscles
Cranial nerves III, IV, and VI are usually tested together as part of the
cranial nerve examination
The cranial nerve exam is a type of neurological examination. It is used to identify problems with the cranial nerves by physical examination. It has nine components. Each test is designed to assess the status of one or more of the twelve crania ...
. The examiner typically instructs the patient to hold his head still and follow only with the eyes a finger or penlight that circumscribes a large "H" in front of the patient. By observing the
eye movement and
eyelids, the examiner is able to obtain more information about the
extraocular muscles
The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...
, the
levator palpebrae superioris muscle, and cranial nerves III, IV, and VI. Loss of function of any of the eye muscles results in
ophthalmoparesis
Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease.
Internal ...
.
Since the oculomotor nerve controls most of the eye muscles, it may be easier to detect damage to it. Damage to this nerve, termed
oculomotor nerve palsy, is known by its ''down and out'' symptoms, because of the position of the affected eye (lateral, downward deviation of gaze).
Pupillary reflex
The oculomotor nerve also controls the constriction of the
pupils and thickening of the lens of the eye. This can be tested in two main ways. By moving a finger toward a person's face to induce
accommodation, their pupils should constrict.
Shining a light into one eye should result in equal constriction of the other eye. Fibers from the optic nerves
cross over in the optic chiasm with some fibers passing to the contralateral optic nerve tract. This is the basis of the "
swinging-flashlight test".
Loss of
accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculomotor nerve.
Additional images
File:Cranial nerve III visceral.svg, Map of the oculomotor nerve.
File:Gray720.png, Median sagittal section of brain.
File:Gray775.png, Plan of oculomotor nerve.
File:Ciliary ganglion pathways.png, Pathways in the Ciliary Ganglion.
File:Midbrainsection.svg, Cross-sectional anatomy of the midbrain showing location of the nucleus of the oculomotor nerve and the Edinger-Westphal nucleus
See also
*
Anisocoria
Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting up to 20% of the population, anisocoria is often entirely harmless, but can be a sign of more serious medical problems.
Causes
Anisocoria is a common condit ...
*
Cranial nerve
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
*
Oculomotor nucleus
References
External links
*
* - "Oculomotor nerve palsy"
*
*
Animations of extraocular cranial nerve and muscle function and damage (University of Liverpool)* ()
{{Authority control
Cranial nerves
Visual system