Logan Steele
The human eye is held in place by a combination of muscles, tendons, and ligaments. There are two types of eye muscles: extrinsic muscles that control eye movement and position, and intrinsic muscles that control near focusing and how much light enters the eye. Six extrinsic muscles, also known as extraocular muscles, are attached to the outside of the eyeball and enable the eyes to move in all directions of sight. These muscles are the superior rectus, medial rectus, inferior rectus, lateral rectus, superior oblique, and inferior oblique. Each eye has six muscles that control movement, and they work in pairs to enable the eyes to move in sync with each other.
| Characteristics | Values |
|---|---|
| Number of muscles | 6 |
| Muscle groups | Rectus, Oblique |
| Rectus muscles | Lateral rectus, Medial rectus, Superior rectus, Inferior rectus |
| Oblique muscles | Superior oblique, Inferior oblique |
| Function of Lateral rectus | Pull the pupil away from the body's midline |
| Function of Medial rectus | Bring the pupil closer to the body's midline |
| Function of Superior rectus | Elevation, helps look up |
| Function of Inferior rectus | Depresses, adducts, and helps rotate the eye |
| Function of Superior oblique | Turns the eye inward |
| Function of Inferior oblique | Moves the eye upward when looking towards the nose |
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What You'll Learn
- Lateral rectus: pulls the pupil away from the body's midline
- Medial rectus: largest extraocular muscle, brings the pupil towards the midline
- Superior rectus: primarily responsible for elevation, helping us look up
- Inferior rectus: depresses, adducts, and helps rotate the eye
- Superior and inferior oblique: responsible for torsional movements
Lateral rectus: pulls the pupil away from the body's midline
The human eye has six muscles, divided into two primary groups: the rectus muscles and the oblique muscles. The four rectus muscles are the lateral rectus, medial rectus, inferior rectus, and superior rectus. The lateral rectus muscle is a muscle of the eye's orbit or eye socket. Its main function is to pull the pupil away from the midline of the body, a process known as abduction. The word "lateral" comes from the Latin "latus", meaning "side", and rectus means "straight".
The lateral rectus originates at the lateral part of the annulus of Zinn, also known as the annular tendon or common tendinous ring, and inserts into the temporal side of the eyeball. The abducens nerve innervates the lateral rectus muscle, providing it with a neural pathway to the brain. This nerve is also known as the sixth cranial nerve.
If the abducens nerve is damaged or ceases to function properly, the eye may experience double vision as the medial rectus muscle works unopposed. This nerve can be damaged by stroke, trauma, tumours, inflammation, or infection. This damage can also cause reduced lateral movement. A specific disorder associated with the lateral rectus muscle is Duane Syndrome, which is believed to be caused by a disturbance of normal embryonic development.
The lateral rectus muscle is crucial for eye movement and vision. Its proper function can be clinically tested by asking the patient to look laterally. Any damage to the lateral rectus muscle can result in impaired eyesight.
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Medial rectus: largest extraocular muscle, brings the pupil towards the midline
The human eye has six muscles, which are split into two primary 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 two oblique muscles are the inferior oblique and the superior oblique.
The medial rectus is the largest of the extraocular muscles. It is also the shortest but strongest of the four recti. It originates from the common ring tendon and the sheath of the optic nerve. It is innervated by the inferior division of cranial nerve III, the oculomotor nerve. The medial recti contract to converge the eyeballs toward the midline. This is the only function of the medial rectus, bringing the pupil closer to the midline of the body.
The medial rectus is one of the six extraocular muscles located in the orbit. Attaching between the bony walls of the orbit and the eyeball, these muscles serve to synchronously move the eyes. The medial rectus arises from a connective tissue ring located at the apex of the orbit, called the common tendinous ring (anulus of Zinn). The muscle attaches to the medial side of the anterior half of the eyeball, therefore adducting the eyeball when contracting.
The medial rectus muscle plays an important role in two types of ocular movements: conjugate and disconjugate. Conjugate movements occur when both eyeballs move in the same direction. The medial rectus takes part in conjugate movements of the eyes in a horizontal plane (i.e. left and right), working together with the lateral rectus. For directing the gaze to one side, the medial and lateral recti must function synchronously.
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Superior rectus: primarily responsible for elevation, helping us look up
The human eye has six muscles, divided into two groups: the recti muscles and the oblique muscles. The superior rectus is one of the four rectus muscles, along with the lateral rectus, the medial rectus, and the inferior rectus. The superior rectus muscle is primarily responsible for elevation, helping us look up. It is one of the extraocular muscles and is innervated by the superior division of the oculomotor nerve (III).
The primary function of the superior rectus muscle is to elevate the eye, causing the cornea to move superiorly. It originates from the annulus of Zinn, which is the common origin point for the rectus muscles, 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). The superior rectus muscle is the only muscle capable of elevating the eye when it is in a fully abducted position.
The movement of the extraocular muscles can be assessed by having a patient look in nine directions, starting with a primary gaze, followed by secondary and tertiary positions. The superior rectus muscle can be isolated by asking the patient to elevate the eye in full abduction.
The superior rectus muscle is related to the other extraocular muscles, particularly the medial rectus muscle and the lateral rectus muscle. It has significant attachments to the levator muscle of the upper eyelid through the fascial sheaths of these two muscles. The superior oblique tendon passes inferior to the superior rectus muscle, and care must be taken during surgical procedures to avoid inadvertently hooking the tendon when the superior rectus muscle is initially hooked.
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Inferior rectus: depresses, adducts, and helps rotate the eye
The human eye has six muscles, split into two primary groups: the rectus muscles and the oblique muscles. The inferior rectus is one of the four rectus muscles, along with the lateral rectus, the medial rectus, and the superior rectus. The inferior rectus muscle is a narrow, strap-shaped muscle of the orbit that extends over the floor of the orbit. It originates from the common tendinous ring, also known as the annulus of Zinn, and attaches at the lower anterior surface of the eyeball.
The primary function of the inferior rectus muscle is to depress the eyeball. It is the only muscle capable of depressing the pupil when the eye is in a fully abducted position. It works in synergy with the superior oblique muscle to depress the pupil, while simultaneously opposing each other. The inferior rectus adducts and extorts (rotates laterally) the eyeball, while the superior oblique abducts and intorts the eyeball. This coordination of actions results in the net action of depressing the eyeball.
The inferior rectus muscle also plays a role in adjusting the direction of the gaze. It passes along the floor of the orbit superior to the infraorbital canal, which houses the infraorbital artery. As it inserts onto the anteromedial part of the sclera, it is covered by the inferior oblique muscle. The fascial sheaths of these two muscles fuse together, giving rise to the inferior check ligament, which attaches to the tarsal plate of the inferior eyelid. This ligament, in turn, enables the inferior gaze by contracting and pulling on the inferior rectus muscle, ultimately depressing the eyelid.
The inferior rectus muscle acts in coordination with other extraocular muscles to control the complex movements of the eyeball. These muscles work together to enable a full range of motion in the eye, allowing for smooth and effective movement in various directions. The inferior rectus muscle is a crucial component of the eye's muscular system, contributing to our visual perception and ability to interact with our surroundings.
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Superior and inferior oblique: responsible for torsional movements
The human eye has six muscles, divided into two groups: the rectus muscles and the oblique muscles. The two oblique muscles are the superior oblique and the inferior oblique. The superior oblique is the longest muscle in the group of six extrinsic muscles of the eye, spanning from the body of the sphenoid bone to the superolateral aspect of the eyeball. The superior oblique originates externally, superomedially to the common tendinous ring, and runs anteriorly, parallel to the medial wall of the orbit.
The primary function of the superior oblique is to turn the eye inward. However, it also has several other functions, including abducting, depressing, and internally rotating the eye. When the eyeball is in a neutral position, the superior oblique abducts the eyeball (directing it laterally from the nose), depresses it (inferiorly), and internally rotates it (moving the superior pole of the eye medially). These functions are not equally efficient in every position of the eye; for instance, internal rotation of the eyeball is most effective when the eye is in the abducted position.
The inferior oblique is primarily responsible for the eye's external rotation. It also elevates and abducts the eye. The inferior oblique is almost entirely muscular, unlike the superior oblique, which is both muscular and tendinous. The inferior oblique is located between the inferior rectus and the orbital floor. It runs along the inferior surface of the eye, eventually inserting on the eye's posterior inferolateral surface. The muscle's width at the insertion point varies, averaging 9 mm.
The superior and inferior oblique muscles work together with the four recti muscles to move the eyes in various directions, including torsional movements (clockwise and counterclockwise) around an axis running through the centre of the pupil to the fovea.
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Frequently asked questions
There are six muscles that hold the eye in place and control its movement.
The six muscles can be divided into two groups: the four rectus muscles and the two oblique muscles. The rectus muscles are the superior, inferior, medial, and lateral rectus muscles. The oblique muscles are the superior and inferior oblique muscles.
The four rectus muscles are responsible for the eye's rotational movement in pitch (up and down). The superior rectus moves the eye upward, the inferior rectus moves it downward, the medial rectus moves the eye inward, and the lateral rectus moves the eye outward.
The two oblique muscles work together with the rectus muscles to move the eye from side to side, up and down, and control its rotation. The superior oblique muscle is primarily responsible for turning the eye inward, while the inferior oblique muscle moves the eye upward when looking towards the nose.
Yes, in addition to the six main extraocular muscles, there is another extrinsic muscle called the levator palpebrae superioris (LPS) that controls the movement of the upper eyelid.
