The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a
cranial nerve 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 a p ...
through the
superior orbital fissure 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 othe ...
that enable most
movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the
intrinsic eye muscles 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
Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of interest ...
.
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
The cerebral aqueduct (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is a conduit for cerebrospinal fluid (CSF) that connects the third ventricle to the fourth ventricle of the ventricular system of the br ...
, 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 distingu ...
. 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 app ...
to emerge from the substance of the brainstem at the oculomotor sulcus (a groove on the lateral wall of the
interpeduncular fossa
The interpeduncular fossa is a deep depression of the ventral surface of the midbrain between the two crura cerebri.
It has been found in humans and macaques, but not in rats or mice, showing that this is a relatively new evolutionary region.
A ...
).
On emerging from the
brainstem, the nerve is invested with a sheath of
pia mater
Pia mater ( or ),[Entry "pia mater"](_blank)
in
arachnoid
Arachnoid may refer to:
* Relating to arachnids
* Arachnoid (astrogeology), a geological structure found only on the planet Venus
* Arachnoid (botany), referring to organs with a cobwebby exterior appearance
* Arachnoid granulation, small protrus ...
. 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 bifur ...
arteries (above), and then pierces the dura mater anterior and lateral to the
posterior clinoid process
In the sphenoid bone, the anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the anterior clinoid processes, while the posterior boundary is formed by a square-shaped plate of bone, the dorsum s ...
, 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 arch ...
.
It traverses the
cavernous sinus
The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.
Structure
The cave ...
, above the other orbital nerves receiving in its course one or two filaments from the
cavernous plexus
The cavernous nerve plexus (also called the Walther plexus) is situated below and medial to that part of the internal carotid artery which is placed by the side of the sella turcica in the cavernous sinus, and is formed chiefly by the medial div ...
of the sympathetic nervous system, and a communicating branch from the
ophthalmic division of the
trigeminal
In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; ...
nerve. As the oculomotor nerve enters the orbit via the
superior orbital fissure 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
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...
and
levator palpebrae superioris
The levator palpebrae superioris ( la, elevating muscle of upper eyelid) is the muscle in the orbit that elevates the upper eyelid.
Structure
The levator palpebrae superioris originates from inferior surface of the lesser wing of the sphenoid bo ...
.
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
The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of ...
.
* Another, to the
inferior rectus
Inferior may refer to:
* Inferiority complex
* An anatomical term of location
* Inferior angle of the scapula, in the human skeleton
* ''Inferior'' (book), by Angela Saini
* ''The Inferior'', a 2007 novel by Peadar Ó Guilín
See also
*Junior (di ...
.
* 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
The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympath ...
, 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
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'', "m ...
(midbrain). There are two nuclei for the oculomotor nerve:
* The
oculomotor nucleus
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From t ...
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 othe ...
except for the
superior oblique muscle
The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only extraocular mu ...
and the
lateral rectus muscle
Lateral is a geometric term of location which may refer to:
Healthcare
*Lateral (anatomy), an anatomical direction
* Lateral cricoarytenoid muscle
* Lateral release (surgery), a surgical procedure on the side of a kneecap
Phonetics
*Lateral co ...
.
* The
Edinger-Westphal nucleus supplies
parasympathetic fibers to the eye via the
ciliary ganglion
The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympath ...
, and thus controls the
sphincter pupillae
The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor ...
muscle (affecting
pupil constriction) and the
ciliary muscle
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea ( vascular layer). It controls accommodation for viewing ...
(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
The general (spinal) somatic efferent neurons (GSE, somatomotor, or somatic motor fibers), arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord. They exit the spinal cord through the ventral roots, carr ...
, 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
General visceral efferent fibers (GVE) or visceral efferents or autonomic efferents, are the efferent nerve fibers of the autonomic nervous system (also known as the ''visceral efferent nervous system'' that provide motor innervation to smooth m ...
, 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
Oculomotor nerve palsy or oculomotor neuropathy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements (fou ...
, 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 i ...
,
*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 d ...
),
*increased intracranial pressure (leading to
uncal herniation
Brain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the brain is squeezed across structures within the skull. The brain can shift across such structures as the falx cerebri, the te ...
)
**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 secondar ...
) or a
**spontaneous
subarachnoid haemorrhage
Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of cons ...
(e.g.,
berry aneurysm), 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 ap ...
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
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems w ...
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 cranial ...
. 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
Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of interest ...
and
eyelid
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyel ...
s, 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 othe ...
, the
levator palpebrae superioris muscle
The levator palpebrae superioris ( la, elevating muscle of upper eyelid) is the muscle in the orbit that elevates the upper eyelid.
Structure
The levator palpebrae superioris originates from inferior surface of the lesser wing of the sphenoid bon ...
, 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
Oculomotor nerve palsy or oculomotor neuropathy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements (fou ...
, 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
pupil
The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...
s 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
*
Cranial nerve
*
Oculomotor nucleus
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From t ...
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