Dominic Stone
The human eye is a fascinating organ, and its movement is controlled by a combination of muscles and nerves. There are six extraocular muscles (also known as extrinsic muscles) that work together to enable the eyes to move in different directions. These muscles are attached to the sclera of the eye at one end and anchored to the bony orbit at the other end. Their contractions produce eye movements, and they are innervated by three cranial nerves. The rectus muscles, consisting of four muscles, are responsible for straight movements, while the oblique muscles, consisting of two muscles, facilitate angular movements. Understanding the coordination and control of eye movements is crucial, as disruptions can indicate underlying conditions, some of which may be serious or even life-threatening.
| Characteristics | Values |
|---|---|
| Number of muscles involved in eyeball movement | 6 |
| Types of muscles involved in eyeball movement | 4 recti muscles and 2 oblique muscles |
| Recti muscles | Superior rectus, inferior rectus, medial rectus and lateral rectus |
| Oblique muscles | Superior oblique and inferior oblique |
| Innervation | Cranial nerves |
| Number of cranial nerves involved | 3 |
| Cranial nerve III | Oculomotor nerve |
| Cranial nerve IV | Trochlear nerve |
| Cranial nerve VI | Abducens nerve |
| Function of recti muscles | Control horizontal eye movements |
| Function of oblique muscles | Control vertical eye movements and eye rotation |
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What You'll Learn
The six extrinsic muscles that control eye movement
Eye muscles are a key part of how our vision works. There are six extrinsic muscles (also called extraocular muscles) that control eye movement and position. These muscles are attached to the outside of the eyeball and enable the eyes to move in all directions of sight.
Superior rectus
The superior rectus muscle is found at the top of the eye and controls upward movement. Movement of the superior rectus muscle is controlled by the oculomotor nerve (CN III).
Inferior rectus
The inferior rectus muscle works with the superior rectus muscle to control vertical eye movements. When the superior rectus contracts to elevate the eye, the inferior rectus relaxes. When the eye is depressed, the inferior rectus contracts and the superior rectus relaxes.
Medial rectus
The medial rectus muscle attaches to the side of the eye closest to the nose and moves the eye inward. Contraction of the medial rectus pulls the eye towards the nose (adduction or medial movement).
Lateral rectus
The lateral rectus muscle works with the medial rectus muscle to control horizontal eye movements. Contraction of the lateral rectus pulls the eye away from the nose (abduction or lateral movement).
Superior oblique
The superior oblique muscle is controlled by the trochlear nerve (CN IV). It works with the inferior oblique muscle to control vertical and torsional eye movements. When the eye is elevated, the superior oblique relaxes as the inferior oblique contracts. When the eye is depressed, the superior oblique contracts and the inferior oblique relaxes.
Inferior oblique
The inferior oblique muscle is controlled by the oculomotor nerve (CN III).
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The three cranial nerves that control the six muscles
Six muscles work together to control the position and movement of the eyes. These muscles are known as extraocular muscles and they are innervated by three cranial nerves. The three nerves that control the six muscles are:
Oculomotor nerve (CN III)
The oculomotor nerve is a nerve pair that carries command signals to the muscles that control eye movement. It is one of three cranial nerve pairs that play a role in eye movement and is the most active of the three. Seven different muscles in and around each eye rely on the oculomotor nerve for signals that tell them what to do. The oculomotor nerve controls all eye movements except for two: rotating the eyeball downward when the eye is pointed inward, and rotating the eyeball outward toward the ear on the same side.
Trochlear nerve (CN IV)
The trochlear nerve controls the movement of rotating each eyeball downward when the eye is pointed inward. A lesion of the trochlear nerve will paralyse the superior oblique muscle. While this will not affect the resting orientation of the eyeball, the patient will experience diplopia (double vision) and may develop a head tilt away from the site of the lesion.
Abducens nerve (CN VI)
The abducens nerve controls the lateral rectus muscle. A lesion of the abducens nerve will paralyse this muscle, causing the affected eye to be adducted by the resting tone of the medial rectus.
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The four recti muscles and their functions
The human eye has six muscles that work together to control eye position and movement. These muscles can be 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 originates at the lateral part of the annulus of Zinn, also known as the annular tendon or
The medial rectus is also a muscle of the eye's orbit. Its only function is to bring the pupil closer to the midline of the body. The word "medial rectus" comes from the Latin "medius", meaning "middle". It is the largest of the extraocular muscles and is innervated by the inferior division of the oculomotor nerve (Cranial Nerve III).
The inferior rectus is also a muscle of the eye's orbit and is located at the bottom of the eye. Its main function is to depress, adduct, and help rotate the eye laterally. It is the only muscle capable of depressing the pupil when it is in a fully abducted position. The word "inferior" comes from the Latin "inferior", meaning "lower".
The superior rectus is located on the top of the eye and its primary function is elevation, helping the eye look up. It also contributes to adduction and medial rotation of the eyeball. The word "superior" comes from the Latin "superior", meaning "above".
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The two oblique muscles and their functions
The two oblique muscles involved in eye movement are the superior oblique and the inferior oblique. They are two of the six extraocular muscles that work together to control the position and movement of the eyeball. The extraocular muscles are innervated by three cranial nerves, and their contractions are controlled by the cranial lower motor neurons.
The superior oblique muscle is involved in depressing, abducting, and laterally rotating the eyeball. A lesion of the trochlear nerve (CN IV) will paralyse the superior oblique muscle, resulting in diplopia, or double vision. The superior oblique also works in conjunction with other muscles to move the eye downward without rotating it. For example, the inferior rectus and superior oblique contract together to pull the eye downward, while the superior rectus and inferior oblique relax.
The inferior oblique muscle is one of the four other extraocular muscles that control vertical eye movements and eye rotation around the mid-orbital axis. To elevate the eye while looking straight ahead, the inferior oblique contracts, along with the superior rectus, while the inferior rectus and superior oblique relax.
Unlike the recti group of muscles, the oblique muscles do not originate from the common tendinous ring. Instead, they take an angular approach to the eyeball, in contrast to the straight approach of the recti muscles, which directly attach to the sclera of the eyeball.
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Eye movement disorders and their causes
Eye movement is controlled by six muscles that work together to control eye position and movement. These muscles are called extraocular muscles and they are innervated by three cranial nerves. The four rectus muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. The two oblique muscles are the superior oblique and inferior oblique.
Eye movement disorders can be present at birth or develop over time and may be associated with other problems, such as injuries. Some examples of eye movement disorders include nystagmus, strabismus, amblyopia, and cranial mononeuropathy. Nystagmus is a condition where the eyes make repetitive movements, which can be constant or intermittent. They can be horizontal, vertical, oblique, torsional (circular), or combinations of these. Strabismus, also known as eye misalignment, can be treated with eye patches, eyeglasses, or contact lenses. Amblyopia, or lazy eye, is treated with eye patches to reduce the risk of amblyopia and loss of sight.
The treatment for eye movement disorders depends on the specific disorder and may include glasses, patches, eye muscle exercises, and surgery. In some cases, no cure exists for certain eye movement disorders, such as most types of nystagmus. When eye movement disorders are suspected to be hereditary, genetic testing and counseling may be recommended. If eye misalignment is believed to be related to a brain issue, an MRI or CT scan of the brain may be performed, along with a lumbar puncture and blood work.
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Frequently asked questions
There are six muscles involved in the control of the eyeball itself.
The four recti muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. The two oblique muscles are the superior oblique and inferior oblique.
The muscles work in pairs. When one muscle moves, its partner in the same eye helps control and balance that movement. The muscles are attached to the sclera of the eye at one end and are anchored to the bony orbit of the eye at their opposite ends. Contraction of the muscles produces movement of the eyes within the orbit.
