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Do these in shuffle mode Cranial nerves - by number, name, action, test study guide by eliwin includes 48 questions covering vocabulary, terms and more. Quizlet flashcards, activities and games help you improve your grades.

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 an extraocular muscle, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch of the oculomotor nerve.

Structure[edit]

The inferior oblique arises from the orbital surface of the maxilla, lateral to the lacrimal groove. Unlike the other extraocular muscles (recti and superior oblique), the inferior oblique muscle does not originate from the common tendinous ring (annulus of Zinn).

Passing lateralward, backward, and upward, between the inferior rectus and the floor of the orbit, and just underneath the lateral rectus muscle, the inferior oblique inserts onto the scleral surface between the inferior rectus and lateral rectus.

In humans, the muscle is about 35 mm long.^[1]

Innervation[edit]

The inferior oblique is innervated by the inferior division of the oculomotor nerve (cranial nerve III).

Function[edit]

Its actions are extorsion, elevation and abduction of the eye.

Primary action is extorsion (external rotation); secondary action is elevation; tertiary action is abduction (i.e. it extorts the eye and moves it upward and outwards). The field of maximal inferior oblique elevation is in the adducted position.

The inferior oblique muscle is the only muscle that is capable of elevating the eye when it is in a fully adducted position.^[2]

Clinical significance[edit]

While commonly affected by palsies of the inferior division of the oculomotor nerve, isolated palsies of the inferior oblique (without affecting other functions of the oculomotor nerve) are quite rare.

'Overaction' of the inferior oblique muscle is a commonly observed component of childhood strabismus, particularly infantile esotropia and exotropia. Because true hyperinnervation is not usually present, this phenomenon is better termed 'elevation in adduction'.^[3]

Surgical procedures of the inferior oblique include: loosening (also known as recession see Strabismus surgery), myectomy, marginal myotomy, and denervation and extirpation. It is also encountered and identified in lower lid blepharoplasty surgeries.

Additional images[edit]

• Eye movement of lateral rectus muscle, superior view

• Eye movement of medial rectus muscle, superior view

• Eye movement of inferior rectus muscle, superior view

• Eye movement of superior rectus muscle, superior view

• Eye movement of superior oblique muscle, superior view

• Eye movement of inferior oblique muscle, superior view

• Anterior view

• Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.

• Inferior oblique muscle

• Extrinsic eye muscle. Nerves of orbita. Deep dissection.

• Extrinsic eye muscle. Nerves of orbita. Deep dissection.

References[edit]

This article incorporates text in the public domain from page 1023 of the 20th edition ofGray's Anatomy(1918)

1. ^Riordan-Eva, P (2011). Vaughan & Asbury's General Ophthalmology (18th ed.). New York: McGraw-Hill Medical. ISBN978-0071634205.
2. ^'Eye Theory'. Cim.ucdavis.edu. Archived from the original on 2014-05-27. Retrieved 2012-12-07.
3. ^Kushner BJ (2006). 'Multiple mechanisms of extraocular muscle 'overaction''. Arch Ophthalmol. 124 (5): 680–8. doi:10.1001/archopht.124.5.680. PMID16682590.

External links[edit]

• Anatomy figure: 29:01-08 at Human Anatomy Online, SUNY Downstate Medical Center
• lesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) (orbit5)

The oculomotor nerve is the third cranial nerve (CN III). It enters the orbit via the superior orbital fissure and innervates extrinsic eye muscles 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 embryonicmidbrain. Cranial nerves IV and VI also participate in control of eye movement.^[1]

Structure[edit]

The oculomotor nerve originates from the third nerve nucleus 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. The fibers from the two third nerve nuclei located laterally on either side of the cerebral aqueduct then pass through the red nucleus. From the red nucleus fibers then pass via the substantia nigra exiting through the interpeduncular fossa.

On emerging from the brainstem, 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 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.

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 of the trigeminal nerve. As the oculomotor nerve enters the orbit it divides into a superior and an inferior branch, which enter the orbit through the superior orbital fissure.^[1]

Superior branch[edit]

The superior branch of the oculomotor nerve or the superior division, the smaller, passes medially over the optic nerve. It supplies the superior rectus and levator palpebrae superioris.

Inferior branch[edit]

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.
• 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[edit]

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 all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle.
• The Edinger-Westphal nucleus supplies parasympathetic 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[edit]

The oculomotor nerve include 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 post ganglionic fibers pass through the short ciliary nerve to the constrictor pupillae of the iris and the cilliary muscles.

Clinical significance[edit]

Disease[edit]

Paralysis of the oculomotor nerve, i.e., oculomotor nerve palsy, can arise due to:

• direct trauma,
• demyelinating diseases (e.g., multiple sclerosis),
• increased intracranial pressure (leading to uncal herniation)
  • due to a space-occupying lesion (e.g., brain cancer) or a
  • spontaneous subarachnoid haemorrhage (e.g., berry aneurysm), and
• microvascular disease, e.g., diabetes.

In people with diabetes 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 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).^[2]

Medial Rectus And Inferior Oblique Dmg Symptoms

Examination[edit]

Eye muscles[edit]

Cranial nerves III, IV, and VI are usually tested together as part of the cranial nerve examination. 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 levator palpebrae superioris muscle, and cranial nerves III, IV, and VI. Loss of function of any of the eye muscles results in ophthalmoparesis.

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[edit]

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. The neurons in the optic nerve decussate in the optic chiasm with some crossing 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[edit]

• Map of the oculomotor nerve.

• Median sagittal section of brain.

• Plan of oculomotor nerve.

• Pathways in the Ciliary Ganglion.

See also[edit]

References[edit]

This article incorporates text in the public domain from page 884 of the 20th edition ofGray's Anatomy(1918)

Superior Oblique Rectus

1. ^ ^abVilensky, Joel; Robertson, Wendy; Suarez-Quian, Carlos (2015). The Clinical Anatomy of the Cranial Nerves: The Nerves of 'On Olympus Towering Top'. Ames, Iowa: Wiley-Blackwell. ISBN978-1-118-49201-7.^{[page needed]}
2. ^Oculomotor Nerve Palsy at eMedicine

Inferior Oblique Rectus

External links[edit]

• MedEd at LoyolaGrossAnatomy/h_n/cn/cn1/cn3.htm
• oph/183 at eMedicine - 'Oculomotor nerve palsy'
• Oculomotor+Nerve at the US National Library of Medicine Medical Subject Headings (MeSH)
• hier-479 at NeuroNames
• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (III)

Inferior Rectus Muscle Injury