Extraocular Muscles of Eye

Human Extraocular Muscles

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 (Frequently Asked Questions)

Question 1) What are Intraocular Muscles?

Answer) The ciliary muscle, sphincter pupillae, and dilator pupillae are all intraocular muscles. The ciliary muscle is a smooth muscle ring that regulates accommodation and the flow of aqueous humour into Schlemm's canal by altering the shape of the lens.

Question 2) What is the Human Eye and Its Function?

Answer) The aqueous delivers oxygen to the eye. Its aim is to bring nutrients to the cornea, iris, and lens, as well as to remove waste products excreted from the lens and to maintain intraocular pressure and thus the shape of the eye. The shape of the eye is determined by this. To work properly, it must be simple.