How Do Extraocular Muscles Control Eye Movements?
The extraocular muscles are located within the orbit but are separate from the eyeball. They are in charge of the movements of the eyeball and the superior eyelid.
The seven extraocular muscles are the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique, and superior oblique. They are functionally divided into two groups: those responsible for eye movement (recti and oblique muscles), and those that are not. Levator palpebrae superioris is in charge of superior eyelid movement.
Eye Movements
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Ductions are one-sided eye movements. Adduction refers to nasal eye movement, whereas abduction refers to temporal eye movement. Sursumduction (supraduction) and deorsum auction (infraduction) are terms used to describe elevation and depression of the eye, respectively. Excycloduction (extortion) is the temporal rotation of the vertical meridian; incycloduction (intorsion) is the nasal rotation of the vertical meridian.
Muscles of Eye Movement
The rectus muscles are assisted in their movements by the two oblique muscles of the eye, which rotate the eye. When the eye is facing forward, the superior oblique rotates the eye medially and abducts it, while the inferior oblique rotates the eye laterally and adducts it. The superior oblique depresses the eye when it is adducted, or turned toward the nose, while the inferior oblique elevates it.
The muscles of the eyes help with vision by performing a variety of specialised functions. When viewing a large area, the muscles perform a scanning function called saccades to provide vital information to the brain. The eyes dart between several points in the field of view during saccades to provide information about the scene to the brain. The fovea, a small region of the retina with the highest concentration of cones, produces the most detailed visual images. Saccades enable the fovea to send clear images of the most important parts of an image to the brain for immediate analysis.
The control of the eyeball is accomplished through the use of six muscles. They can be classified into two groups that are the four recti muscles, and the two oblique muscles.
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Six Extraocular Muscles of Eye
Superior rectus muscle.
Inferior rectus muscle.
Lateral rectus muscle.
Medial rectus muscle.
Superior oblique muscle.
Inferior oblique muscle.
Recti Muscles
Superior rectus, inferior rectus, medial rectus, and lateral rectus are the four recti muscles.
The popular tendinous ring is where these muscles get their start. This is a fibrous tissue ring that covers the back of the orbit's optic canal. The muscles migrate anteriorly from their root to connect to the sclera of the eyeball.
The name recti comes from the Latin word rectus, which means "straight" and refers to the fact that the recti muscles have a straight path from origin to attachment. On the other hand, the oblique eye muscles have an angled approach to the eyeball.
Superior Rectus
Attaches to the posterior and anterior aspects of the sclera and originates from the superior part of the typical tendinous ring.
Elevation is the primary movement. Contributes to the eyeball's adduction and medial rotation.
Oculomotor nerve innervation (CN III).
Inferior Rectus
Attaches to the inferior and anterior aspects of the sclera and originates from the inferior part of the typical tendinous ring.
Depression is the main movement. It also helps with eyeball adduction and lateral rotation.
Oculomotor nerve innervation (CN III).
Medial Rectus
Attaches to the anteromedial portion of the sclera and originates from the medial part of the typical tendinous ring.
The eyeball is adducted in this action.
Oculomotor nerve innervation (CN III).
Lateral Rectus
Attaches to the anterolateral side of the sclera and originates from the lateral part of the typical tendinous ring.
Abducts the eyeball from its socket.
Abducens nerve innervation (CN VI).
Extrinsic Eye Muscles
These muscles reside in the eye socket (orbit) and are responsible for moving the eye up, down, side to side, and rotating it. The superior rectus is an extraocular muscle that connects the top of the eye to the rest of the body. It draws the viewer's attention upward.
Oblique Muscles
The superior and inferior obliques are the two oblique muscles. They do not derive from the traditional tendinous ring, unlike the recti group of muscles.
From their point of origin, the oblique muscles approach the eyeball in an angular fashion (in contrast to the straight approach of the recti muscles). They are attached to the posterior surface of the sclera.
Superior Oblique Muscle Action
This muscle is responsible for intorsion, depression, as well as abduction in the neutral role. The superior oblique is responsible for depression, abduction, and intorsion during adduction. This muscle is responsible for intorsion, abduction, as well as depression during abduction. This muscle attaches to the eye's posterior, superior, lateral surface. The Annulus of Zinn is the source (via the trochlea). The superior oblique runs along the orbit's medial surface.
Attachments: The sphenoid bone's body is where it all begins. The superior rectus' tendon passes through a trochlea and connects to the sclera of the eye posterior to the superior rectus.
Actions: Depresses, abducts, and rotates the eyeball medially.
Innervation: Trochlear nerve (CN IV).
Inferior Oblique
This muscle is responsible for extortion, elevation, and abduction in the neutral role. The inferior oblique is responsible for elevation, abduction, and extortion during adduction. This muscle is in control of extortion, abduction, and elevation during abduction. This muscle attaches to the eye's posterior, inferior, lateral surface. The maxillary bone is the source of the problem. The inferior oblique runs from the orbit's medial wall to the eye's inferolateral aspect.
Attachments: Originates from the orbital floor's anterior aspect. Attaches to the eye's sclera, just below the lateral rectus.
Actions: Elevates, abducts, and rotates the eyeball laterally.
Innervation: Oculomotor nerve (CN III).
FAQs on Extraocular Muscles of the Eye: Comprehensive Guide
1. What are the extraocular muscles and what is their primary role?
The extraocular muscles are a set of seven muscles located within the orbit (eye socket) but outside the eyeball itself. Their primary role is to control the precise movements of the eye, such as looking up, down, side-to-side, and rotating the eyeball. They are also responsible for raising the upper eyelid, allowing for a full field of vision.
2. How many extraocular muscles are there, and what are their names?
There are seven extraocular muscles in each eye. Six of these muscles move the eyeball, while one controls the eyelid. They are:
- Four Rectus Muscles: Superior Rectus, Inferior Rectus, Medial Rectus, and Lateral Rectus.
- Two Oblique Muscles: Superior Oblique and Inferior Oblique.
- Eyelid Muscle: Levator Palpebrae Superioris.
3. What is the difference between extraocular and intraocular muscles?
The main difference lies in their location and function. Extraocular muscles are attached to the outside of the eyeball and control its movement and position within the orbit. In contrast, intraocular muscles, such as the ciliary muscle and sphincter pupillae, are located inside the eyeball and control the shape of the lens (for focusing) and the size of the pupil (to regulate light entry).
4. What are the specific actions of the rectus muscles (superior, inferior, medial, and lateral)?
The four rectus muscles have distinct primary actions that move the eye along straight axes:
- Medial Rectus: Moves the eye inward, toward the nose (adduction).
- Lateral Rectus: Moves the eye outward, toward the temple (abduction).
- Superior Rectus: Primarily moves the eye upward (elevation) and also helps with adduction and intorsion.
- Inferior Rectus: Primarily moves the eye downward (depression) and also helps with adduction and extorsion.
5. How do the actions of the superior and inferior oblique muscles differ from the rectus muscles?
While the rectus muscles primarily move the eye up, down, left, and right, the oblique muscles are crucial for rotational and diagonal movements.
- The Superior Oblique muscle primarily causes intorsion (rotating the top of the eye toward the nose) and also helps move the eye downward and outward.
- The Inferior Oblique muscle primarily causes extorsion (rotating the top of the eye away from the nose) and helps move the eye upward and outward.
6. Which cranial nerves are responsible for controlling the extraocular muscles?
The movements of the extraocular muscles are controlled by three specific cranial nerves:
- The Oculomotor Nerve (Cranial Nerve III) innervates the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris.
- The Trochlear Nerve (Cranial Nerve IV) innervates only the superior oblique muscle.
- The Abducens Nerve (Cranial Nerve VI) innervates only the lateral rectus muscle.
7. What is the common mnemonic used to remember the nerve supply for eye muscles?
A popular and easy-to-remember mnemonic is (LR6SO4)3 or LR6(SO4)O3. This formula helps recall which nerve controls which muscle:
- LR6: The Lateral Rectus is supplied by Cranial Nerve VI (Abducens).
- SO4: The Superior Oblique is supplied by Cranial Nerve IV (Trochlear).
- O3: All Other extraocular muscles are supplied by Cranial Nerve III (Oculomotor).
8. How do the extraocular muscles coordinate to produce smooth, precise eye movements for tracking objects?
The brain coordinates the extraocular muscles through a system of agonist-antagonist pairs. For an eye to move in one direction, one muscle (the agonist) contracts while its opposing muscle (the antagonist) relaxes. For example, to look right, the right eye's lateral rectus contracts while its medial rectus relaxes. This precise, synchronised action, controlled by the brainstem, allows for smooth pursuit movements, rapid shifts in gaze (saccades), and keeps both eyes aligned on a single target, ensuring binocular vision.
9. What are intorsion and extorsion, and why are these rotational movements important for stable vision?
Intorsion is the inward rotation of the top of the eye towards the nose, primarily controlled by the superior oblique muscle. Extorsion is the outward rotation of the top of the eye towards the temple, controlled by the inferior oblique muscle. These torsional movements are crucial for maintaining a stable, upright visual field. When you tilt your head, these muscles rotate the eyes in the opposite direction to counteract the tilt, preventing the world from appearing tilted and helping you maintain balance and focus.
10. What is the clinical importance of assessing extraocular muscle function?
Assessing extraocular muscle function is a fundamental part of a neurological exam because it helps doctors diagnose various conditions. Weakness or paralysis of a specific muscle can point to damage to its controlling cranial nerve, as seen in oculomotor, trochlear, or abducens palsy. These issues can be caused by head trauma, stroke, diabetes, or a tumour. Problems with coordination, such as strabismus (misaligned eyes), can also be identified, allowing for timely treatment to prevent long-term issues like double vision (diplopia).
