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The extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles control eye movement, while the seventh, the levator palpebrae superioris, controls eyelid elevation. The six muscles responsible for eye movement are the four recti muscles, and the superior and inferior oblique muscles. The actions of these muscles depend on the position of the eye at the time of contraction. The extraocular muscles are innervated by three cranial nerves, and damage to one of these nerves will cause paralysis of its respective muscles.
| Characteristics | Values |
|---|---|
| Number of extraocular muscles | 6 or 7 |
| Number of rectus muscles | 4 |
| Names of rectus muscles | Superior rectus, lateral rectus, medial rectus, inferior rectus |
| Number of oblique muscles | 2 |
| Names of oblique muscles | Superior oblique, inferior oblique |
| Muscle controlling eyelid elevation | Levator palpebrae superioris |
| Cranial nerves controlling the muscles of the orbit | Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducens nerve (CN VI) |
| Main blood vessels supplying the extraocular muscles | Ophthalmic artery, lacrimal artery, infraorbital artery |
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What You'll Learn
There are 6 or 7 extraocular muscles
The extraocular muscles, also referred to as extrinsic ocular muscles, are the group of muscles that control eye movement and eyelid elevation. They are located within the orbit but are extrinsic and separate from the eyeball itself. There are 6 or 7 extraocular muscles, depending on how they are categorised.
There are 4 rectus muscles, which are named according to their relative positions of attachment: the superior rectus, lateral rectus, medial rectus, and inferior rectus. There are also 2 oblique muscles: the superior and inferior obliques. The rectus muscles are all of almost equal length, at around 40mm, but the lengths of their associated tendons differ. The superior oblique is the longest muscle of all the extraocular muscles. The oblique muscles take an angular approach to the eyeball, in contrast to the straight approach of the recti muscles. The superior oblique muscle is the only muscle that receives innervation from the trochlear nerve (the fourth cranial nerve).
The seventh muscle is the levator palpebrae superioris, which controls eyelid elevation. It does not contact the globe directly but elevates the eyelid. It originates from the lesser wing of the sphenoid and courses anteriorly. The levator palpebrae superioris is supplied by the oculomotor nerve (CN III).
The extraocular muscles are innervated by three cranial nerves: the oculomotor nerve (CN III), the trochlear nerve (CN IV), and the abducens nerve (CN VI). These nerves coordinate the motion of the lateral rectus in one eye and the medial action on the other.
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They control eye movement
The extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles control eye movement, while the seventh, the levator palpebrae superioris, controls eyelid elevation. The six muscles responsible for eye movement are the four recti muscles and the superior and inferior oblique muscles.
The four recti muscles are the superior rectus, lateral rectus, medial rectus, and inferior rectus. They are named according to their relative positions of attachment and their straight paths. The medial rectus is the muscle closest to the nose, while the lateral rectus is the thinnest extraocular muscle. The superior rectus originates from the upper part of the common tendinous ring, while the inferior rectus originates from the medial part of the common tendinous ring. The recti muscles are all of almost equal length, at around 40 mm, but the lengths of their associated tendons differ.
The two oblique muscles are the superior and inferior obliques. The superior oblique is the longest muscle of all the extraocular muscles. It originates from the back of the orbit, a little closer to the medial rectus, and gets rounder as it courses forward. The inferior oblique originates at the lower front of the nasal orbital wall, passes inferiorly over the inferior rectus muscle, and inserts under the lateral rectus muscle. The oblique muscles take an angular approach to the eyeball, in contrast to the straight approach of the recti muscles.
The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction. Four of the extraocular muscles control movement in the cardinal directions: north, east, south, and west (or up, right, down, and left). The other two muscles are responsible for counteracting head movements and adjusting eye movement accordingly.
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They are supplied by the ophthalmic artery
The extraocular muscles are located within the orbit and are extrinsic to the eyeball. They control the movements of the eyeball and the superior eyelid. There are 6 extraocular muscles that control eye movement and one that controls eyelid elevation. The 6 muscles that control eye movement are the superior rectus, inferior rectus, lateral rectus, superior oblique, inferior oblique, and medial rectus.
The primary blood supply for the extraocular muscles is the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The ophthalmic artery is the first branch of the internal carotid artery and provides the majority of the ocular blood supply. It enters the orbit through the optic canal and runs close to the optic nerve, giving off the long and short posterior ciliary arteries that pierce the sclera and supply the choroid. The ophthalmic artery also gives off the central artery of the retina, which finds its way deep into the nerve to appear on the surface of the retina.
The muscular branches of the ophthalmic artery form the anterior ciliary arteries that enter the eye and connect with the major arterial circle of the ciliary body. The lateral muscular branch supplies the lateral rectus, superior rectus, superior oblique, and levator palpebrae superioris muscles. The medial muscular branch supplies the inferior rectus, medial rectus, and inferior oblique muscles. The lacrimal artery, another branch of the ophthalmic artery, partially supplies the lateral rectus muscle. The infraorbital artery, a branch of the maxillary artery, also provides a partial supply to the inferior oblique and inferior rectus muscles.
The ophthalmic artery has a wide variation in its branching pattern as it approaches the eye. The blood supply to the extraocular muscles is crucial, and any damage to the supplying arteries can have significant consequences. For example, a disruption to the blood supply during surgery of the inferior rectus muscle can lead to complications.
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They are extrinsic and separate from the eyeball
The extraocular muscles are a group of six muscles that attach to the outside of the eyeball and are responsible for eye movements. These muscles are distinct from the intrinsic muscles, which are located within the eyeball and serve a different function. Being extrinsic, they originate from bony structures within the orbit and insert into the fibrous layer of the eyeball, specifically the sclera, except for one, which inserts into the retina. This structural arrangement allows for a wide range of eye movements, including up and down, side to side, and rotational movements. The ability to move the eyeball independently of the head is crucial for tasks such as reading, where the eyes must move across a line of text, or tracking a moving object.
These muscles are unique in that they move the eyeball, which is relatively small and lightweight, rather than a bone or joint, as is the case with most skeletal muscles. This requires precise control and coordination, which is achieved through a combination of neural input and the specific anatomical arrangement of the muscles. The fact that they are extrinsic, or external, to the eyeball is fundamental to their function, as it allows for this independent movement and control.
The extrinsic nature of these muscles also contributes to their role in protecting the eyeball. For example, the orbital fat and extrinsic muscles act as a cushion, absorbing any impacts to the eye area and helping to prevent damage to the delicate structures within the eyeball itself. This protective mechanism is essential, given the vulnerability of the eye and its critical role in vision. The separation of the extraocular muscles from the eyeball also allows for a greater range of movement.
If these muscles were intrinsic, or internal to the eyeball, the range and variety of eye movements would be significantly limited. The current arrangement, with the muscles attaching externally, allows for a full range of motion, including convergence, where the eyes move inward toward each other, and divergence, where they move outward. This wide field of movement is essential for tasks such as depth perception and peripheral vision, which require the eyes to move in a variety of directions independently of head movement.
The separation of the extraocular muscles from the eyeball also facilitates their individual function and control. Each muscle has a specific role and is innervated by cranial nerves, allowing for precise control over eye movements. This individual innervation means that each muscle can be activated independently, contributing to the fine-tuned and coordinated movements required for tasks such as reading or tracking a moving object. The extrinsic nature of these muscles is thus fundamental to their function and the overall visual system.
In summary, the fact that the extraocular muscles are extrinsic and separate from the eyeball is essential for their function and the overall visual capabilities of the human body. This arrangement allows for a wide range of eye movements, protects the delicate structures within the eyeball, and enables independent control of each muscle for precise and coordinated eye movements. Understanding the unique anatomy and function of these muscles is crucial in fields such as ophthalmology and neurology, highlighting the importance of their extrinsic and separate nature.
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They are a specialised skeletal muscle form
Extraocular muscles are a specialised skeletal muscle form with a large ratio of nerve fibres to skeletal muscle fibres. They have a ratio of 1:3 to 1:5 compared to other skeletal muscles, which are 1:50 to 1:125. The muscle fibres in the extraocular muscles are small and have a complex composition with regard to the major proteins determining contraction force and velocity (myosin heavy chains [MyHC]). The extraocular muscles have various fibre types, including slow tonic types, which resist fatigue, and saccadic (rapid) muscle fibres.
The extraocular muscles are located within the orbit and are extrinsic and separate from the eyeball itself. They control the movements of the eyeball and the superior eyelid. There are seven extraocular muscles: four rectus muscles, two oblique muscles, and the levator palpebrae superioris. The four rectus muscles are the medial rectus, lateral rectus, superior rectus, and inferior rectus. The two oblique muscles are the superior and inferior obliques. The levator palpebrae superioris controls eyelid elevation.
The movements of the extraocular muscles are influenced by a system of extraocular muscle pulleys, soft tissue pulleys in the orbit. The pulley system is fundamental to the movement of the eye muscles and ensuring conformity to Listing's law. The extraocular muscles are supplied by branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The blood vessels that supply the extraocular muscles also supply most of the anterior segment of the eye, so care must be taken during surgery to avoid disrupting this blood supply.
The extraocular muscles are innervated by three cranial nerves: the oculomotor nerve (CN III), the trochlear nerve (CN IV), and the abducens nerve (CN VI). Each rectus and oblique muscle has a functional insertion point at the closest point where the muscle first contacts the globe, forming a tangential line from the globe to the muscle origin known as the arc of contact. The common site of origin for the rectus muscles is the Annulus of Zinn, located at the orbital apex.
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Frequently asked questions
Extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles control eye movement, and the seventh controls eyelid elevation.
The seven extraocular muscles are the four recti muscles (superior, lateral, medial, and inferior rectus), and the superior and inferior oblique muscles, and the levator palpebrae superioris.
The four recti muscles are named after their relative positions of attachment. The superior rectus muscle, for example, originates from the upper part of the common tendinous ring, while the lateral rectus muscle originates from the lateral part.
The two oblique muscles are the inferior and superior obliques. The superior oblique originates from the back of the orbit and is the longest of all the extraocular muscles.
The levator palpebrae superioris is responsible for raising the upper eyelid, and this can be a voluntary or involuntary action.
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