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The human eye has six muscles that control its movement. Four of these are rectus muscles, which move the eye in the cardinal directions, and two are oblique muscles, which rotate the eye and assist the rectus muscles. The inferior rectus muscle is the only muscle capable of depressing the pupil when it is in a fully abducted position. The superior oblique muscle also depresses the eye when the eye is in an abducted position, and the inferior oblique elevates the eye when the eye is adducted.
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What You'll Learn
- The inferior rectus is the only muscle that depresses the eye when fully abducted
- The superior oblique muscle is responsible for abduction, depression and internal rotation
- The superior rectus muscle elevates the eye, allowing it to look up
- The inferior oblique elevates the eye when it is turned towards the nose
- The lateral rectus pulls the pupil away from the body's midline
The inferior rectus is the only muscle that depresses the eye when fully abducted
The human eye has six muscles, split into two groups: the rectus muscles and the oblique muscles. The four rectus muscles are the lateral rectus, the medial rectus, the inferior rectus, and the superior rectus. The inferior rectus muscle is one of the seven extraocular muscles and is primarily responsible for depressing the eye (downgaze). The word "inferior" comes from the Latin for "lower", which is fitting given that the muscle is located at the bottom of the eye.
The inferior rectus is also capable of adduction and excycloduction (extorsion or rotating the eye laterally). The inferior oblique muscle has a similar function to the inferior rectus, but it moves the eye upward when the eye is looking in toward the nose. The superior rectus muscle, meanwhile, is mostly responsible for elevation, helping us to look up.
The inferior rectus is the only muscle capable of depressing the pupil when the eye is fully abducted. This is because, when the eye is abducted, the axis of the globe is in line with the axis/force vector of the superior rectus, allowing it to pull straight back and elevate the eye. However, the force vector of the inferior oblique in this position is approximately perpendicular, meaning it cannot elevate the eye. This isolates the depressing action of the inferior rectus by preventing the superior oblique from acting as an efficient depressor.
Surgery on the inferior rectus muscle can lead to various complications, including potential damage to the parasympathetic fibres to the sphincter pupillae and ciliary muscle. Unsatisfactory ocular alignment is the most common complication and may require additional surgery to correct. Other potential complications include diplopia, perforation of the sclera, and postoperative infections.
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The superior oblique muscle is responsible for abduction, depression and internal rotation
The human eye has six muscles, which are split into two groups: the recti muscles and the oblique muscles. The recti muscles include the inferior rectus, which is responsible for depressing the eye, and the superior rectus, which helps the eye look up.
The oblique muscles include the superior oblique muscle, which is responsible for abduction, depression, and internal rotation. This muscle is the longest in its group, spanning from the body of the sphenoid bone to the superolateral aspect of the eyeball. The superior oblique muscle originates from the body of the sphenoid bone, medial to the origin of the levator palpebrae superioris muscle and superomedial to the optic canal.
The superior oblique muscle's function is to produce eye movements that direct the gaze inferolaterally by abducting, depressing, and internally rotating the eye. This muscle is the only extraocular muscle innervated by the trochlear nerve (the fourth cranial nerve). It loops through a pulley-like structure (the trochlea of the superior oblique) and inserts into the sclera on the posterotemporal surface of the eyeball.
The primary action of the superior oblique muscle is internal rotation, also known as intorsion. The secondary action is depression, which is most effective when the eye is in an adducted position. The tertiary action is abduction, or lateral rotation. The superior oblique is tested during neurological examinations by having the patient look inwards and downwards, testing the muscle's depressing action.
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The superior rectus muscle elevates the eye, allowing it to look up
The human eye has six muscles, divided into two groups: the recti muscles and the oblique muscles. The four recti muscles are the lateral rectus, the medial rectus, the inferior rectus, and the superior rectus. The superior rectus muscle is located at the top of the eye and is primarily responsible for elevating the eye, allowing it to look up. The name "superior rectus" is derived from Latin, where "superior" means "above" and "rectus" means "straight".
The superior rectus muscle originates from the annulus of Zinn and courses anteriorly and superiorly over the globe, making an angle of 23 degrees with the visual axis. This angle causes the secondary and tertiary actions of the superior rectus muscle to be adduction and intorsion (incycloduction). Each of the extraocular muscles has a functional insertion point, which is at the closest point where the muscle first contacts the globe. This point forms a tangential line from the globe to the muscle origin and is known as the arc of contact. The superior rectus has an arc of contact of 6.5 mm, similar to the inferior rectus muscle.
The superior rectus muscle plays a crucial role in coordinating eye movement and eyelid position. It works in conjunction with other muscles to enable smooth and effective eye movement. The rectus muscles, including the superior rectus, act as the pure depressor and elevator of the eye when it is in abduction. This means that they are responsible for moving the eye up and down when it is looking straight ahead or slightly away from the midline.
The superior rectus muscle receives its blood supply primarily from the superior muscular branches of the ophthalmic artery, with some contribution from two anterior ciliary arteries. The primary blood supply for all extraocular muscles, including the superior rectus, is provided by the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The superior rectus muscle is innervated by the superior division of cranial nerve III (oculomotor nerve).
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The inferior oblique elevates the eye when it is turned towards the nose
The human eye has six muscles, divided into two groups: the recti muscles and the oblique muscles. The recti muscles include the inferior rectus, which is responsible for depressing the eye. The two oblique muscles are the inferior oblique and the superior oblique.
The inferior oblique muscle is named for its position within the orbit, relative to the eyeball. It occupies the inferior aspect of the orbit, encircling the lower portion of the eyeball. The primary action of this muscle is to elevate and abduct (move laterally) the eyeball. It works in conjunction with the other extraocular muscles to control eye movement, positioning the pupil, and adjusting the gaze direction.
The inferior oblique muscle has three actions on the eyeball: it elevates the anterior part of the eyeball, depresses the posterior part, and rotates the visual axis upwards and outwards. This is important for functions like looking up from reading, where the eyes move from a state of convergence. The inferior oblique muscle also works with the check ligaments and retrobulbar fat to prevent retraction of the eyeball by the rectus.
The inferior oblique muscle is similar to the inferior rectus muscle in function, but it moves the eye upward when the eye is looking inward toward the nose. When the eye is in the adducted (medial) position, the primary action of the inferior oblique muscle is to move the eye up. This is in contrast to the superior rectus muscle, which intorts the eye.
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The lateral rectus pulls the pupil away from the body's midline
The human eye has six muscles, divided into two groups: the recti muscles and the oblique muscles. The four recti muscles are the lateral rectus, the medial rectus, the inferior rectus, and the superior rectus. The lateral rectus muscle pulls the pupil away from the body's midline.
The lateral rectus originates at the lateral part of the annulus of Zinn, also known as the annular tendon or common tendinous ring. It then inserts into the temporal side of the eyeball. The annulus of Zinn is a tendinous ring that surrounds the optic nerve and serves as the origin for four of the six extraocular muscles. The word "lateral rectus" comes from the Latin "latus," meaning "side," and "rectus," meaning "straight."
The lateral rectus muscle abducts the eye, turning the eye laterally in the orbit. It is one of the six extraocular muscles. The primary action of the inferior rectus muscle, on the other hand, is to depress the eye, causing the cornea and pupil to move inferiorly. It is also one of the four rectus muscles. The inferior rectus originates from the annulus of Zinn and courses anteriorly and laterally along the orbital floor, making an angle of 23 degrees with the visual axis.
The inferior rectus muscle is the only muscle capable of depressing the pupil when it is in a fully abducted position. It has multiple functions, including depressing, adducting, and helping to extort (rotate laterally) the eye. The superior rectus muscle, located on the top of the eye, helps the eye look up. The superior oblique muscle is on the upper medial side of the eye, meaning it is closer to the nose. Its primary job is to turn the eye inward.
A sixth nerve palsy, also known as abducens nerve palsy, is a neurological defect that results from a damaged or impaired abducens nerve. This damage can be caused by a stroke, trauma, tumour, inflammation, or infection. If the left abducens nerve is damaged, the left eye will not abduct fully, and the patient will be unable to abduct the eye. This can lead to horizontal double vision and reduced lateral movement.
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Frequently asked questions
The inferior rectus muscle is the primary muscle responsible for depressing the eye.
Depressing the eye means causing the cornea and pupil to move inferiorly, or downward.
The inferior rectus muscle also helps to adduct and extort (rotate laterally) the eye. It is the only muscle capable of depressing the pupil when it is in a fully abducted position.
There are six muscles involved in controlling the eye's movement. Four rectus muscles (lateral rectus, medial rectus, inferior rectus, and superior rectus) and two oblique muscles (inferior oblique and superior oblique).
The superior oblique muscle is responsible for abduction, depression, and internal rotation of the eyeball.
