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The human eye has six muscles that control eye movement and contribute to vision. These muscles are called extraocular muscles and are located within the orbit but are extrinsic to the eyeball. They can be divided into two groups: the four recti muscles and the two oblique muscles. The recti muscles include the superior rectus, inferior rectus, medial rectus, and lateral rectus, while the oblique muscles include the superior oblique and inferior oblique. The recti muscles originate from the common tendinous ring and attach to the sclera of the eyeball, while the oblique muscles have a more angular approach to the eyeball. The superior oblique, for example, acts like a pulley, threading through a bony opening called the trochlea before attaching to the eyeball. These eye muscles are innervated by cranial nerves, and damage to these nerves can cause paralysis and affect eye movement and positioning.
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What You'll Learn
- The superior oblique muscle attaches behind the eye and loops through the trochlea
- The inferior oblique muscle inserts on the inferior, posterior, and lateral eye portion
- The medial rectus muscle originates from the common tendon and brings the pupil closer to the body's midline
- The lateral rectus muscle originates from the annulus of Zinn and inserts into the eyeball's temporal side
- The levator palpebrae superioris muscle originates from the sphenoid bone and attaches to the superior tarsal plate
The superior oblique muscle attaches behind the eye and loops through the trochlea
The superior oblique muscle is one of the six muscles that control the movements of the eyeball. It is also one of the two oblique muscles, the other being the inferior oblique muscle. The superior oblique muscle originates from the body of the sphenoid bone, medial to the origin of the levator palpebrae superioris muscle and superomedial to the optic canal.
Embryologic studies show that the muscle, the insertion tendon, and the cartilaginous pulley develop together in a straight line in the early stages. At around 12 weeks, the tendon turns around the trochlear cartilage, creating the pulley action. The superior oblique muscle receives its innervation through the trochlear nerve (CN IV), which is the only cranial nerve that emerges from the posterior aspect of the brainstem.
The superior oblique muscle is responsible for abduction (directed laterally from the nose), depression (inferiorly), and internal rotation (movement of the superior pole of the eye medially). These functions are not equally efficient in every position of the eye. For example, internal rotation is most effective when the eye is in the abducted position, while depression is strongest when the eye is in the adducted position.
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The inferior oblique muscle inserts on the inferior, posterior, and lateral eye portion
The human eye has six muscles that control the direction in which the eyes point, thereby contributing to vision. These muscles are known as extraocular muscles (EOMs). The four rectus muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. The two oblique muscles are the superior oblique and the inferior oblique.
The inferior oblique muscle is the shortest of all the eye muscles, measuring approximately 37 mm in length. Unlike the other EOMs, the inferior oblique does not originate from the annulus of Zinn or the common tendinous ring. Instead, it arises from the orbital floor lateral to the nasolacrimal groove. From its origin, the muscle runs along the inferior surface of the eye, passing between the floor of the orbit and the inferior rectus. It then wraps around the bottom of the eye and inserts on the eye's posterior inferolateral surface. The insertion point of the inferior oblique tendon is in the sclera under the lateral rectus. The width of the inferior oblique muscle at the insertion point varies, averaging 9 mm.
The inferior oblique muscle inserts at the posterior quadrant of the eyeball (inferolateral part), between the lateral and inferior recti muscles, and slightly posterior to the insertion of the superior oblique muscle. The inserting tendons of the inferior and superior oblique muscles pass each other and lie in the same oblique vertical plane. The fascial sheath of the inferior oblique blends with the thickened sheath of the inferior rectus muscle. These two then blend with the medial and lateral check ligaments, which are triangular sheet expansions of the medial and lateral recti muscles. This fusion of the inferior rectus, inferior oblique, and the check ligaments forms the suspensory ligament of the eyeball, a hammock-like sling that provides support to the eyeball.
The inferior oblique muscle is responsible for the eye's external rotation. Its secondary and tertiary actions are elevation and abduction, respectively. The contraction of the inferior oblique muscle pulls the eyeball in a direction posterior to its vertical axis, rotating the eye laterally around this axis. Thus, the inferior oblique simultaneously exhibits three actions on the eyeball: it elevates the anterior part of the eyeball, depresses the posterior part of the eyeball, and abducts the eyeball. By elevating and abducting the eyeball, the inferior oblique rotates the visual axis upwards and outwards.
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The medial rectus muscle originates from the common tendon and brings the pupil closer to the body's midline
The human eye has six muscles that control the movement of the eyeball and the superior eyelid. These muscles are called extraocular muscles and are located within the orbit of the eye. The medial rectus is one of these six muscles. It is the shortest but strongest of the four recti muscles. The medial rectus originates from the common tendon, also known as the common tendinous ring, or the anulus of Zinn. This is a ring of fibrous tissue that surrounds the optic canal at the back of the orbit. The medial rectus muscle passes anteriorly from its origin to attach to the sclera of the eyeball.
The medial rectus is innervated by the inferior branch of the oculomotor nerve (CN III). The oculomotor nerve is a somatic motor nerve, which allows for voluntary control over the medial rectus muscle. The medial rectus is supplied with blood from the ophthalmic artery, a branch of the internal carotid artery.
The medial rectus muscle is the only muscle of the eye's orbit that brings the pupil closer to the midline of the body. This is known as adduction of the eyeball. When contracting, the medial recti muscles adduct the eyeball, pulling the eye medially. This action is important in two types of ocular movements: conjugate and disconjugate. Conjugate movements are when both eyeballs move in the same direction. The medial rectus takes part in conjugate movements of the eyes in a horizontal plane, working together with the lateral rectus muscle. For directioning the gaze to one side, the medial and lateral recti must function synchronously.
The medial rectus muscle runs cushioned in the periorbital fat tissue, superior to the floor of the orbit and inferior to the superior oblique muscle, ophthalmic artery, and nasocilia.
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The lateral rectus muscle originates from the annulus of Zinn and inserts into the eyeball's temporal side
The human eye has six muscles that control the direction in which the eyes point, contributing to vision. These muscles are different from other skeletal muscles in the human body, as they consist of a selected variety of fibre types, allowing them to make rapid (saccadic) movements and resist fatigue. The rectus muscles are also more precise than other muscle insertions.
The lateral rectus muscle is one of the four recti muscles, along with the superior rectus, inferior rectus, and medial rectus. The lateral rectus muscle originates from the annulus of Zinn, also known as the common tendinous ring. The annulus of Zinn is a ring of fibrous tissue that surrounds the optic canal at the back of the orbit. The muscle then extends forward (anteriorly) and inserts into the sclera on the lateral side of the eyeball, specifically about 6.9 mm to 7 mm from the limbus of the cornea. The sclera is the white, fibrous outer layer of the eye. The lateral rectus muscle is flat and strap-shaped, and it is wider in its anterior part.
The lateral rectus muscle is responsible for abducting the eyeball, allowing it to move side to side. It works in synergy or opposition with other extrinsic muscles of the eye to produce coordinated movements and direct the gaze. The abducens nerve (cranial nerve VI) innervates the lateral rectus muscle, providing motor control and allowing for voluntary contraction. This nerve exclusively supplies the lateral rectus muscle, so other extraocular muscles are not affected.
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The levator palpebrae superioris muscle originates from the sphenoid bone and attaches to the superior tarsal plate
The levator palpebrae superioris muscle is a thin, triangular muscle that extends along the roof of the orbit, from the apex of the orbit to the superior eyelid. It is the only muscle involved in raising the superior eyelid, allowing for an unhindered upward gaze. The levator palpebrae superioris originates from the sphenoid bone, specifically from the inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen.
As the levator palpebrae superioris muscle fans out, its fibres attach to various structures. The deep fibres attach to the anterior surface of the superior tarsus, while the superficial fibres radiate through the eyelid and orbicularis oculi, attaching to the skin of the superior eyelid. The most lateral fibres of the muscle's aponeurosis attach to the orbital tubercle of the zygomatic bone, while the most medial fibres attach to the medial palpebral ligament.
The levator palpebrae superioris is closely associated with the superior tarsal muscle, a smooth muscle that originates from its undersurface. The superior tarsal muscle is attached to the levator palpebrae superioris and inserts on the superior tarsal plate, a thick plate of connective tissue. The superior tarsal muscle is innervated by the sympathetic nervous system, which elevates the eyelid in states of "fight or flight" response, leading to additional widening of the palpebral fissure during moments of excitement, fear, surprise, and other emotions.
The levator palpebrae superioris muscle receives its blood supply primarily from the internal carotid artery via branches of the ophthalmic artery, including the muscular branches, the supraorbital artery, the lacrimal artery, the supratrochlear artery, and the superior peripheral arcade. Blood is drained into the superior ophthalmic vein. Additionally, the muscle receives motor innervation from the superior division of the oculomotor nerve (CN III), with lesions in CN III resulting in ptosis or eyelid drooping.
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Frequently asked questions
The extraocular muscles are located within the orbit but are extrinsic to the eyeball. They originate from the common tendinous ring and attach to the sclera of the eyeball.
The superior oblique muscle inserts on the superior, lateral, and posterior part of the eye. It originates on the lesser wing of the sphenoid bone and loops through a connective tissue sling called the trochlea.
The inferior oblique muscle inserts on the inferior, posterior, and lateral portion of the eye. It originates on the medial maxillary bone.
