Victor Forge
The human eye is a fascinating organ that relies on several muscles to function. These muscles are responsible for the eye's movement and also contribute to our vision. There are six muscles that control the direction in which our eyes point, and they work in pairs to control and balance each other's movements. This is why our eyes can only turn so far. There are also two types of paired movement: conjugate movement, where the eyes move in the same direction, and disjunctive, where they move in opposite directions. The muscles responsible for these movements are called extraocular muscles, and they work in conjunction with three cranial nerves.
| Characteristics | Values |
|---|---|
| Number of eye muscles | 6 |
| Type of eye muscles | Extraocular muscles |
| Extraocular muscles | Four recti muscles, superior and inferior oblique muscles |
| Function of the lateral rectus | Pull the pupil away from the midline of the body |
| Function of the medial rectus | Bring the pupil closer to the midline of the body |
| Function of the superior rectus | Elevation |
| Function of the inferior rectus | Depression, adduction, lateral rotation |
| Function of the superior oblique | Depresses, abducts, medially rotates the eyeball |
| Function of the inferior oblique | Moves the eye upward when the eye is looking in toward the nose |
| Innervation | Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducens nerve (CN VI) |
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What You'll Learn
Superior and inferior oblique muscles
The superior and inferior oblique muscles are two of the six extraocular muscles that control eye movement. These muscles, unlike the rectus muscles, do not originate from the common tendinous ring. Instead, they take an angular approach to the eyeball, attaching to the posterior surface of the sclera.
The superior oblique muscle works like a pulley. It starts at the upper back of the eye and extends forward, threading through a small bony opening on the upper-inner side of the eye socket called the trochlea. After passing through the trochlea, it attaches to the top of the eyeball, just behind the superior rectus. The superior oblique muscle is innervated by the trochlear nerve (CN IV), and its main movement is depression or downward rotation of the eyeball.
The inferior oblique muscle, or obliquus oculi inferior, is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. It is one of the extraocular muscles and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique muscle arises from the orbital surface of the maxilla, lateral to the lacrimal groove. It passes lateralward, backward, and upward, between the inferior rectus and the floor of the orbit, and just underneath the lateral rectus muscle. It then inserts onto the scleral surface between the inferior rectus and the eyeball. The inferior oblique muscle is innervated by the inferior branch of the oculomotor nerve (CN III). Its primary action is to elevate and abduct (laterally move) the eyeball.
The superior and inferior oblique muscles work in synergy with their respective partner muscles, the superior rectus and inferior rectus, to elevate the pupil. At the same time, their rotatory actions oppose and neutralize each other to prevent rotation of the eyeball during its elevation. Additionally, the inferior oblique muscle acts with the check ligaments and the retrobulbar fat to prevent retraction of the eyeball by the rectus muscles.
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Rectus muscles
The rectus muscles, also known as recti muscles, are a group of four muscles that control eye movement and eye alignment. The word "rectus" is derived from the Latin word "straight", indicating that these muscles have a direct path from their origin to their attachment. The four rectus muscles are:
- Superior rectus: This muscle is found at the top of the eye and controls upward movement. The movement of the superior rectus muscle is controlled by the oculomotor nerve (CN III).
- Inferior rectus: Located at the bottom of the eye, this muscle allows the eye to move downward. The inferior rectus muscle's movement is also controlled by the oculomotor nerve (CN III).
- Medial rectus: The medial rectus muscle attaches to the side of the eye closest to the nose and moves the eye inward. Its movement is controlled by the oculomotor nerve (CN III).
- Lateral rectus: This muscle attaches to the side of the eye closest to the temple and enables the eye to move outward. The lateral rectus muscle is controlled by the abducens nerve (CN VI).
These four rectus muscles work together with the two oblique muscles to move the eye up and down, from side to side, and control its rotation. The rectus muscles originate from the common tendinous ring, a fibrous ring of connective tissue that surrounds the optic nerve where it connects to the orbit. They pass anteriorly to attach to the sclera of the eyeball, contributing to the complex coordination of eye movements and vision.
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Cranial nerve system
The human eye contains six muscles that control the direction in which the eyes point, contributing to vision. The movement of the eyeball is dependent on signals that travel through three cranial nerves: the oculomotor nerve (CN III), the trochlear nerve (CN IV), and the abducens nerve (CN VI).
The Cranial Nerve System
The cranial nerve system consists of 12 nerves that emerge from the brain, specifically from the brainstem, which connects the brain and spinal cord. The numbering of the cranial nerves is based on their position from front to back (rostral-caudal) and their exit location on the skull. The olfactory nerve (I) and optic nerve (II) emerge from the forebrain, while the other ten pairs arise from the brainstem.
The oculomotor nerve (CN III) controls the movements of the superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle. The main movement of the superior rectus muscle is elevation, while the inferior rectus muscle's main movement is depression. The medial rectus muscle contributes to adduction and medial rotation of the eyeball. The trochlear nerve (CN IV) controls the superior oblique muscle, which, like the other oblique muscles, takes an angular approach to the eyeball. The abducens nerve (CN VI) controls the lateral rectus muscle, which abducts the eyeball.
Cranial nerves can be purely motor, purely sensory, or mixed, carrying sensory and/or motor information between the body and the brain. If a nerve carries information to smooth muscle, cardiac muscle, or glands, it is a visceral efferent nerve. If it carries information to the skin or skeletal muscle, it is a somatic efferent nerve.
Damage to a cranial nerve can cause specific movement or sensory issues, depending on its underlying function. Conditions affecting the functioning of cranial nerves include head trauma, nervous system disorders, circulatory issues, and autoimmune conditions.
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Voluntary and involuntary control
The human eye is a fascinating organ, with six muscles that control its movement and, consequently, the direction in which we look. These muscles are called the extraocular muscles, four of which are rectus muscles, and the other two are oblique muscles. The four rectus muscles are the superior rectus, lateral rectus, medial rectus, and inferior rectus. The two oblique muscles are the superior oblique and inferior oblique.
The extraocular muscles work in pairs, with one muscle moving and its partner controlling and balancing that movement. This is why human eyes can only turn so far. The six muscles responsible for eye movement depend on signals that travel through three cranial nerves: Cranial nerve III (CN III), also known as the oculomotor nerve, Cranial nerve IV (CN IV) or the trochlear nerve, and Cranial nerve VI (CN VI) or the abducens nerve.
The oculomotor nerve controls the movements of the superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle. The trochlear nerve controls the superior oblique muscle, which works like a pulley, starting at the upper back of the eye and extending forward, then threading through a small bony opening on the upper-inner side of the eye socket. The abducens nerve controls the lateral rectus muscle, which pulls the pupil away from the midline of the body.
While most eye movement is accomplished without conscious effort, the precise integration between voluntary and involuntary control of the eye is a subject of continuing research. The vestibulo-ocular reflex, for example, plays an important role in the involuntary movement of the eye. The levator palpebrae superioris, which raises the upper eyelid, can also be a voluntary or involuntary action.
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Eye muscle disorders
- Superior oblique: This muscle works like a pulley, starting at the upper back of the eye and extending forward, then threading through a small bony opening on the upper-inner side of the eye socket called the trochlea. After passing through the trochlea, it attaches to the top of the eyeball just behind the superior rectus.
- Inferior oblique: This muscle attaches to the lower-inner side of the eye socket and extends laterally, wrapping around the bottom of the eye and attaching just behind the lateral rectus on the far side.
- Superior rectus: This muscle originates from the superior part of the common tendinous ring and attaches to the superior and anterior aspect of the sclera. Its main movement is elevation, but it also contributes to adduction and medial rotation of the eyeball.
- Inferior rectus: This muscle originates from the inferior part of the common tendinous ring and attaches to the inferior and anterior aspect of the sclera. Its main movement is depression, but it also contributes to adduction and lateral rotation of the eyeball.
- Medial rectus: This muscle originates from the medial part of the common tendinous ring and attaches to the anteromedial aspect of the sclera.
- Lateral rectus: This muscle originates from the anterior aspect of the orbital floor and attaches to the sclera of the eye, posterior to the lateral rectus.
Some common eye movement disorders include:
- Strabismus: a disorder in which the two eyes don't line up in the same direction, resulting in "crossed eyes" or "walleye."
- Nystagmus: fast, uncontrollable movements of the eyes, sometimes called "dancing eyes."
- Amblyopia: also known as "lazy eye," this condition results in reduced vision in one or both eyes despite the absence of any pathology in the eye itself.
Treatments for eye movement disorders vary widely and depend on the specific condition. Some conditions may resolve on their own, while others may require medication or surgery. In the case of strabismus, treatment may involve patching, eyeglasses, surgery, or a combination of these therapies.
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Frequently asked questions
There are six muscles that control eye movement, also known as extraocular muscles.
The four rectus muscles are the superior rectus, lateral rectus, medial rectus, and inferior rectus. The two oblique muscles are the superior oblique and inferior oblique.
The six muscles work in pairs, with one muscle moving and its partner controlling and balancing that movement. The muscles also depend on signals from three cranial nerves: the oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI).
