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Extraocular muscles are a group of specialised skeletal muscles that control eye movements and eyelids. They are broadly divided into voluntary and involuntary muscles. There are six extraocular muscles that control eye movement and one that controls eyelid elevation. The six muscles of the orbit are engaged depending on the position of the eye at the time of muscle contraction. These muscles control movement in the cardinal directions: north, east, south, west (or up, right, down, left). The two remaining extraocular muscles are responsible for counteracting head movements and adjusting eye movement accordingly.
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What You'll Learn
There are six or seven extraocular muscles
The seventh muscle, the levator palpebrae superioris, is responsible for eyelid elevation. It is considered an extraocular muscle even though it does not directly contribute to eye movement. The orbitalis muscle is sometimes included as an eighth extraocular muscle, but it is usually not considered part of this group.
The extraocular muscles are a specialized form of skeletal muscle with a high ratio of nerve fibres to skeletal muscle fibres. They receive their blood supply from the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The primary nerve supply to the extraocular muscles comes from the third, fourth, and sixth nerves, specifically the oculomotor, trochlear, and abducent nerves, respectively.
The function of the extraocular muscles can be assessed through a clinical eye exam, which involves drawing a large letter "H" in the air in front of the patient's face and asking them to follow the movement with their eyes while keeping their head still. This test allows for the evaluation of the six muscles that control eye movement in different directions.
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They control eye movement
The extraocular muscles are a group of specialised skeletal muscles that control eye movement and the elevation of the eyelid. There are six extraocular muscles that control eye movement, and one or two that control eyelid elevation. The six muscles of the orbit are engaged depending on the position of the eye at the time of muscle contraction. Four of these control movement in the cardinal directions: north, east, south, and west (or up, right, down, and left). The remaining two extraocular muscles are responsible for counteracting head movements and adjusting eye movement accordingly.
The four rectus muscles are the superior, inferior, medial, and lateral rectus. The superior rectus is engaged when looking upwards and inward, and the inferior rectus is contracted when the eye is looking downwards and outwardly. The medial rectus is used when the eye is turned inwards (towards the nose) and horizontally, and the lateral rectus is used when the eye is turned out (away from the nose) and horizontally. The medial rectus inserts closest to the limbus, followed by the inferior rectus, then the lateral rectus, and finally the superior rectus, which inserts farthest from the limbus.
The two oblique muscles are the superior oblique and the inferior oblique. The superior oblique is used for internal rotation in a neutral gaze and depression in adduction. Interestingly, turning the eye upwards and outwardly uses the inferior oblique muscle, and turning it downward and inward uses the superior oblique.
The levator palpebrae superioris is the muscle responsible for eyelid elevation. It does not contact the globe directly but instead inserts into the superior eyelid. The orbitalis muscle is sometimes included as an eighth extraocular muscle, although it is usually not considered part of this group.
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They include rectus, oblique and levator palpebrae superioris muscles
The extraocular muscles are the most specialised skeletal muscles in the human body. They are broadly divided into two categories: voluntary and involuntary muscles. The former includes seven extraocular muscles that control the movements of the eye and eyelids, and are important for binocular single vision. These include four rectus muscles, two oblique muscles, and the levator palpebrae superioris.
The four rectus muscles are the superior, inferior, medial, and lateral rectus. They are named so because they have a direct path from origin to attachment, in contrast to the oblique muscles, which take an angular approach to the eyeball. The two oblique muscles are the superior and inferior oblique. These six muscles are responsible for the movement of eyes into different gazes.
The rectus muscles arise from the annulus of Zinn and proceed anteriorly to reach the globe. The point of tangency is where the muscle first comes in contact with the globe, and this determines the vector of force exerted by the muscle. The arc of contact is the circular area the muscle travels from the first point of contact (point of tangency) to the anatomical insertion point.
The levator palpebrae superioris is responsible for eyelid elevation. It is the only muscle involved in raising the superior eyelid. A small portion of this muscle contains a collection of smooth muscle fibres, known as the superior tarsal muscle. The levator palpebrae superioris does not contact the globe directly.
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They have a large ratio of nerve fibres to skeletal muscle fibres
Extraocular muscles are a group of specialised skeletal muscles that control eye movements and the eyelids. They are considered the most specialised skeletal muscles in the human body. These muscles can be broadly divided into two categories: voluntary and involuntary. The former includes seven extraocular muscles that control the movements of the eye and eyelids, while the latter includes muscles such as the superior tarsal muscle (Muller's muscle), inferior tarsal muscle, and orbitalis.
The six muscles responsible for eye movement are the four rectus muscles (superior, inferior, medial, and lateral rectus) and the two oblique muscles (superior and inferior oblique). These muscles work together to enable the eyes to look in different directions, including up, down, left, and right. Additionally, two of these extraocular muscles are responsible for counteracting head movements and adjusting eye movement accordingly.
The seventh voluntary muscle is the levator palpebrae superioris, which is responsible for eyelid elevation. While it does not directly contribute to eye movement, it is often considered one of the extraocular muscles. The orbitalis muscle is sometimes included as an eighth extraocular muscle, although it is usually not considered part of this group.
The extraocular muscles have a unique feature in that they have a large ratio of nerve fibres to skeletal muscle fibres. This ratio ranges from 1:3 to 1:5, in contrast to other skeletal muscles, which have a much lower ratio of 1:50 to 1:125. This high nerve fibre content is essential for the precise control and coordination of eye movements.
The primary blood supply for the extraocular muscles is provided by the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The ophthalmic artery, in particular, plays a crucial role in supplying blood to the extraocular muscles, with its branches, the ciliary arteries, providing oxygenated blood to the rectus muscles.
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The blood supply for the muscles comes from the ophthalmic artery
Extraocular muscles are the most specialised skeletal muscles in the human body, divided into voluntary and involuntary groups. The voluntary muscles include seven extraocular muscles that control the movements of the eye and eyelids and are important for binocular single vision. These include four recti muscles, two oblique muscles, and the levator palpebrae superioris. The four recti muscles are the superior, inferior, medial, and lateral rectus, and the two oblique muscles are the superior and inferior oblique. These six muscles are responsible for the movement of the eyes into different gazes. The levator palpebrae superioris is responsible for eyelid elevation.
The blood supply for the extraocular muscles comes from the ophthalmic artery, which is the first branch of the internal carotid artery. The ophthalmic artery enters the orbit through the optic canal and, in most individuals, runs inferiorly to the optic nerve. The ophthalmic artery gives off several branches that supply the orbit, meninges, face, and upper nose. The branches of the ophthalmic artery that supply the extraocular muscles include the central retinal artery, the posterior ciliary arteries, and the inferior and superior muscular vessels.
The central retinal artery is the first and most important branch of the ophthalmic artery. It supplies the optic nerve and the inner 6/7 layers of the retina. The central retinal artery is considered an end artery, meaning that it is the only artery supplying a given tissue, with no collateral circulation. As a result, occlusion of the central retinal artery can quickly result in blindness and is considered an ophthalmic emergency.
The posterior ciliary arteries consist of two sets of arteries: the long and short posterior ciliary arteries. These arteries pierce the sclera on the posterior aspect of the eyeball, just lateral to the optic nerve, and supply the sclera, choroid, and anterior segment of the eyeball. The long posterior ciliary arteries also supply the iris and ciliary body. The short posterior ciliary arteries supply the posterior choriocapillaris, peripapillary choroid, and the majority of the anterior optic nerve.
The inferior and superior muscular vessels are branches of the ophthalmic artery that supply the extraocular muscles. These vessels often form superior and inferior groups and accompany the oculomotor nerve to supply the extraocular muscles. Additionally, they give off anterior ciliary arteries to supply the ciliary plexus and anterior conjunctival arteries to supply the conjunctiva.
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Frequently asked questions
Extraocular muscles are the most specialized skeletal muscles in the human body. They are divided into voluntary and involuntary muscles. There are 6 of these extraocular muscles that control eye movement and one muscle that controls eyelid elevation.
There are 7 extraocular muscles: 4 rectus muscles, 2 oblique muscles, and the levator palpebrae superioris.
The 4 rectus muscles control movement in the cardinal directions: north, east, south, and west (or up, right, down, and left). The 2 oblique muscles are responsible for counteracting head movements and adjusting eye movement. The levator palpebrae superioris controls eyelid elevation.
