Dominic Stone
The human eye has six muscles that control its movement. These muscles are responsible for directing the eyes side-to-side, up and down, and diagonally. They are also integral to the function and motion of the eyes, with the extraocular muscles controlling the external movement of the eye, and the intraocular muscles responsible for pupil accommodation and reaction to light. The superior rectus muscle, for example, elevates the eye, while the inferior rectus muscle depresses and laterally rotates the eye. The superior oblique muscle, located on the upper medial side of the eye, turns the eye inward. These muscles, along with the nerves that connect them to the brain, play a crucial role in our visual capabilities, including depth perception and three-dimensional vision.
| Characteristics | Values |
|---|---|
| Number of muscles in the human eye | 6 |
| Types of muscles | Extraocular muscles, Intraocular muscles, Protractors and retractors of the eyelids |
| Extraocular muscles | Lateral rectus, Medial rectus, Superior rectus, Inferior rectus, Superior oblique, Inferior oblique |
| Intraocular muscles | Ciliary muscle, Sphincter pupillae, Dilator pupillae |
| Function of the ciliary muscle | Controls the shape of the lens and the flow of aqueous humor into Schlemm's canal |
| Function of the sphincter pupillae | Constricts the pupil's diameter |
| Function of the dilator pupillae | Increases the pupillary diameter |
| Primary retractor of the upper eyelid | Levator palpebrae superioris |
| Primary protractor of the eyelids | Orbicularis oculi muscles |
| Ocular movements | Vertical, Transverse, Anteroposterior |
| Cranial nerves | Cranial nerve III (CN III) or oculomotor nerve, Cranial nerve IV (CN IV) or trochlear nerve, Cranial nerve VI (CN VI) or abducens nerve |
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What You'll Learn
The human eye has six muscles
The four rectus 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 common tendinous ring, and inserts into the temporal side of the eyeball. It pulls the pupil away from the body's midline. The medial rectus is on the side closest to the nose, while the inferior rectus is at the bottom of the eye and helps extort (rotate laterally) the eye. The superior rectus is located at the top of the eye and is responsible for elevating the eye, helping us look up.
The two oblique muscles are the inferior oblique and the superior oblique. The inferior oblique moves the eye upward when looking towards the nose. The superior oblique, located on the upper medial side of the eye, turns the eye inward.
These six muscles work in coordination with three cranial nerves: the oculomotor nerve, the trochlear nerve, and the abducens nerve. They are also known as Cranial Nerve III, Cranial Nerve IV, and Cranial Nerve VI, respectively. These nerves control the movements of the different eye muscles.
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Eye muscles control eye movement
The human eye has six muscles that control eye movement. These muscles are what allow you to direct your eyes side-to-side, up and down, or at diagonal angles. The muscles that control eye movement attach to the outside of the eyeball, which is why they are sometimes referred to as "external" or "extrinsic" muscles. These muscles work in pairs, with one muscle's partner in the same eye helping to control and balance its movement. This is why human eyes can only turn so far.
The six muscles can be divided into two groups: the four recti muscles and the two 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 lateral rectus is a muscle of the eye's orbit, and its main function is to pull the pupil away from the midline of the body. The word "lateral" comes from the Latin "latus", meaning "side". The inferior rectus is also a muscle of the orbit, and its main function is to extort the eye. The superior rectus is mostly in charge of elevation, helping the eye look up. The superior oblique muscle is on the upper medial side of the eye, meaning it is closer to the nose. Its primary function is to turn the eye inward. The inferior oblique has a similar function to the inferior rectus, but it is the muscle that moves the eye upward when the eye is looking in toward the nose, rather than away.
There are also intraocular muscles, which are responsible for pupil accommodation and reaction to light. These include the ciliary muscle, the sphincter pupillae, and the dilator pupillae. The ciliary muscle is a smooth muscle ring that controls accommodation by altering the shape of the lens, as well as controlling the flow of aqueous humour into Schlemm's canal. The sphincter pupillae and dilator pupillae are also composed of smooth muscle. The sphincter pupillae encircles the pupil and is responsible for the constriction of its diameter, while the dilator muscle is arranged radially and increases the pupillary diameter.
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Types of eye muscles: rectus and oblique
The human eye has six muscles that control its movement. These muscles are split into two primary groups: the rectus muscles and the oblique muscles. Each eye has four rectus muscles and two oblique muscles.
The four rectus muscles are the superior rectus, the inferior rectus, the medial rectus, and the lateral rectus. The superior rectus muscle originates from the superior part of the annulus of Zinn and proceeds along the orbital wall to insert into the sclera at a distance of approximately 7.7mm from the limbus. The primary function of this muscle is to elevate the eye, but it also contributes to adduction and intorsion. The word "superior" means "up" or "top", reflecting its position in the eye. The inferior rectus, on the other hand, depresses and laterally rotates the eye, and contributes to adduction and extorsion. The name "inferior" means "down" or "bottom", as it is located at the bottom of the eye. The medial rectus inserts closest to the limbus, around 5.5mm away, with "medial" meaning "middle", as it is the side closest to the nose. The lateral rectus inserts at 6.9mm from the limbus and pulls the pupil away from the body's midline, with "lateral" meaning "to the side".
The two oblique muscles are the superior oblique and the inferior oblique. The superior oblique muscle originates in the posterior orbit and travels medially before inserting into the sclera in the superotemporal globe. It is located on the upper medial side of the eye, closer to the nose. Its primary function is to turn the eye inward, but it also abducts, depresses, and medially rotates the eye. The inferior oblique, meanwhile, originates on the orbital floor and inserts on the sclera in the inferotemporal globe. It has a similar function to the inferior rectus, but it moves the eye upward when looking towards the nose, abducts, elevates, and laterally rotates the eye.
The rectus and oblique muscles work together to control the movement of the eyes and enable vision. They are essential for functions such as depth perception and three-dimensional (3D) vision.
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Intraocular muscles control pupil accommodation and reaction to light
The human eye has six muscles, 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 superior oblique muscle is on the upper medial side of the eye, while the inferior oblique moves the eye upward when the eye is looking in toward the nose. The superior rectus elevates the eye and the inferior rectus depresses and laterally rotates the eye.
The intraocular muscles are a subset of the six muscles of the eye and include the ciliary muscle, the sphincter pupillae, and the dilator pupillae. The ciliary muscle is a smooth muscle ring that controls accommodation by altering the shape of the lens, as well as controlling the flow of aqueous humour into Schlemm's canal. The ciliary muscle is attached to the zonular fibres, which suspend the lens. When the ciliary muscle contracts, the tension on the lens is lessened, causing it to become more spherical to focus on nearby objects. Relaxing the ciliary muscle has the opposite effect, optimising focus on distant objects. The ciliary muscle is also responsible for the lens accommodation response, increasing the curvature of the lens and, in turn, its refractive power.
The sphincter pupillae and dilator pupillae are also composed of smooth muscle. The sphincter pupillae encircles the pupil and constricts its diameter, while the dilator muscle is arranged radially and increases the pupillary diameter. The parasympathetic system controls the constricting action of the sphincter pupillae, while the sympathetic system controls pupil dilation. The iris sphincter muscle is innervated by the postganglionic parasympathetic axons (short ciliary nerve fibres) of the ciliary ganglion.
The intraocular muscles are responsible for pupil accommodation and reaction to light. Pupil accommodation involves the constriction of the pupil when the viewer directs their eyes from a distant object to a nearby object. This process is known as the accommodation response. The depth of focus of the eye is increased during pupil constriction, as the light scattered by the periphery of the cornea is blocked. The opposite process, pupil dilation, occurs in response to emotional stimuli and increased illumination.
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Superior and inferior rectus muscles elevate and depress the eye
The human eye has six muscles, which are split into two groups: the recti muscles and the oblique muscles. The recti muscles are further divided into four types: the lateral rectus, the medial rectus, the inferior rectus, and the superior rectus. The oblique muscles are the inferior oblique and the superior oblique.
The superior rectus muscle is one of the extraocular muscles and is innervated by the superior division of the oculomotor nerve (III). It is the only muscle that can elevate the eye when it is in a fully abducted position. Its primary function is elevation, although it also contributes to intorsion and adduction. The superior rectus originates from the annulus of Zinn and inserts into the anterosuperior surface of the eye.
The inferior rectus is also an extraocular muscle and is primarily responsible for depressing the eye (downgaze). It originates from the annulus of Zinn and courses anteriorly and laterally along the orbital floor, making an angle of 23 degrees with the visual axis. The inferior rectus also has secondary and tertiary actions of adduction and extorsion (excycloduction). It is innervated by the lower division of cranial nerve III (oculomotor).
The superior and inferior rectus muscles, therefore, work together to elevate and depress the eye. However, it is important to note that these muscles also contribute to other eye movements, such as adduction and extorsion, and their functions can be isolated through specific eye movements. For example, abducting the eye isolates the elevating action of the superior rectus and the depressing action of the inferior rectus.
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Frequently asked questions
There are six muscles in the eye, split into two groups: the rectus muscles and the oblique muscles.
The muscles in the eye control eye movement and are integral to its function and motion. They allow the eye to move side-to-side, up and down, and diagonally.
The four rectus 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.
If the eye's muscles are not functioning properly, it could be due to an eye muscle condition or a nervous system-related disorder. This can cause issues with depth perception and three-dimensional (3D) vision.
