Maximus Gage
The human eye is a fascinating organ, with several parts working together to help us see. One of the key components of our vision is the movement of our eyeballs, which is controlled by a set of muscles. These muscles work in pairs to enable our eyes to move in all directions and focus on objects near and far. In this article, we will explore the specific muscles responsible for moving the eyeball up and how they work in conjunction with other muscles to maintain our vision.
| Characteristics | Values |
|---|---|
| Number of muscles involved in eye movement | 6 |
| Muscles involved in upward eye movement | Superior rectus, inferior oblique |
| Muscles involved in downward eye movement | Inferior rectus, superior oblique |
| Muscles involved in eyelid elevation | Levator palpebrae superioris, superior tarsal muscle |
| Innervation for eyelid elevation | Oculomotor nerve (CN III), sympathetic nervous system |
| Main movement of superior oblique | Elevation |
| Main movement of inferior oblique | Depression |
| Innervation of superior oblique | Trochlear nerve (CN IV) |
| Innervation of inferior oblique | Oculomotor nerve (CN III) |
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Superior rectus
The superior rectus is an extrinsic muscle of the eye, located outside the eyeball but within the orbit. It is one of the extraocular muscles, which work together to move the eyes within the orbit. The superior rectus muscle is innervated by the superior branch of the oculomotor nerve (CN III). This nerve originates from the nucleus of the oculomotor nerve, which is a somatic motor nucleus, thus providing voluntary control over the superior rectus muscle.
The superior rectus muscle originates from the annulus of Zinn, which is a connective tissue ring located at the apex of the orbit, surrounding the optic canal. It inserts into the anterosuperior surface of the eye, with a width of around 11 mm and approximately 8 mm from the corneal limbus. The insertion of the superior rectus muscle is also located around 7.5 mm from the insertion of the medial rectus muscle, 7.1 mm from the insertion of the lateral rectus muscle, and about 7.9 mm from the corneal limbus.
The superior rectus muscle is responsible for elevation, adduction, and internal rotation of the eyeball. When looking straight ahead, it contracts with the inferior oblique muscle to elevate the eye without rotating it. Contraction of the superior rectus causes the eye to move simultaneously in multiple planes: elevation in the transverse plane, adduction in the vertical plane, and internal rotation (intorsion) in the anteroposterior plane. These contrasting movements are achieved due to the muscle fibres coursing obliquely at a 23-degree angle with the median plane of the eye.
The superior rectus muscle is associated with various medical conditions and may exhibit weakness, paralysis, overactivity, or congenital absence in some individuals. Problems with nerve conduction of the oculomotor nerve (CN III) can lead to weakness or paralysis of the muscle, which may be congenital or acquired through head injuries. Treatment options for conditions affecting the superior rectus muscle include eye surgery to weaken or reposition the muscle, generally resulting in positive outcomes.
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Inferior oblique
The inferior oblique is a thin, narrow muscle of the eye. It is one of the six extraocular muscles, also referred to as the extrinsic muscles of the orbit. The inferior oblique is primarily responsible for the eye's external rotation. The muscle's secondary and tertiary actions are elevation and abduction, respectively. The inferior oblique is the only muscle that is capable of elevating the eye when it is in a fully adducted position.
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique 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 is innervated by the inferior branch of the oculomotor nerve. The inferior oblique arises from the orbital surface of the maxilla, lateral to the lacrimal groove.
The inferior oblique is almost entirely muscular, unlike the superior oblique, which is both muscular and tendinous. Inferior oblique overaction is a common cause of vertical strabismus and can be seen in conditions like infantile esotropia. Inferior oblique dysfunction can affect ocular torsion, leading to diplopia. Surgery on the inferior oblique is a common procedure to correct strabismus. Understanding the inferior oblique's anatomy and function is essential for diagnosing and managing various ocular conditions, particularly those involving eye movement and alignment.
The embryological origin of the inferior oblique involves the coordinated action of multiple genes and signalling pathways that regulate the migration, proliferation, and differentiation of myogenic precursor cells from the cranial mesoderm. The inferior oblique is the shortest of all the eye muscles, measuring approximately 37 mm long. The inferior oblique tendon inserts in the sclera under the lateral rectus. The inferior oblique has two surfaces: the superior ocular and the inferior orbital surfaces.
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Superior oblique
The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle that originates in the upper, medial side of the orbit (from beside the nose). It is the only extraocular muscle innervated by the trochlear nerve (the fourth cranial nerve). The superior oblique muscle loops through a pulley-like structure (the trochlea of the superior oblique) and inserts into the eyeball on the posterotemporal surface of the eyeball.
The superior oblique is one of the two noteworthy oblique extraocular muscles. These muscles are unique in that they do not originate from the common tendinous ring, have an angular attachment to the eyeball, and attach to the posterior aspect of the eyeball. The superior oblique functions explicitly to move the eye in the down-and-out position and intort the eye. The superior oblique muscle attaches to the trochlea—a fibrous, cartilaginous pulley attached to the trochlear fovea of the frontal bone.
The primary action of the superior oblique muscle is intorsion (internal rotation), the secondary action is depression (primarily in the adducted position), and the tertiary action is abduction (lateral rotation). The extraocular muscles rotate the eyeball around vertical, horizontal, and antero-posterior axes. The superior oblique is the longest muscle in this group, spanning from the body of the sphenoid bone to the superolateral aspect of the eyeball. The function of the superior oblique muscle is to produce eye movements that direct the gaze inferolaterally by abducting, depressing, and internally rotating the eye.
The superior oblique muscle gets its vascular supply from the lateral muscular branch of the ophthalmic artery, which also supplies blood to the lateral and superior rectus muscles, as well as the levator palpebrae superioris muscle. The innervation of the superior oblique muscle is distinct from the remaining extraocular muscles in that its nerve supply is from the trochlear nerve (CN IV). The trochlear nerve is the only cranial nerve that emerges from the posterior aspect of the brainstem. It takes a long path through the endocranium and enters the orbit via the superior orbital fissure to innervate the superior oblique muscle.
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Trochlear nerve
The trochlear nerve, also known as cranial nerve IV or CN IV, is one of 12 sets of cranial nerves. It is responsible for supplying movement information to the superior oblique muscle, which is connected to the eye near its top. The nerve starts in the brainstem and passes through four areas before reaching the superior oblique muscle: the trochlear nucleus, the ambient cistern, the cavernous sinus, and the orbit.
The trochlear nerve is the smallest cranial nerve by the number of axons, but it has the longest intracranial course. It is the only nerve to have a dorsal exit from the brainstem, originating in the midbrain and extending laterally and anteriorly to the superior oblique muscle. The nerve is named after the Latin word "trochleae", which means "pulley", as the muscle threads through a small bony opening on the upper-inner side of the eye socket called the trochlea.
The trochlear nerve is a motor nerve that sends signals from the brain to the muscles that control eye movement. It allows the superior oblique muscle to move, making it possible to look down and toward and away from the nose. The nerve also controls the abduction and intorsion of the eye.
Damage to the trochlear nerve will likely affect eye movement and vision. Trochlear nerve palsy commonly presents with vertical diplopia, which is exacerbated when looking downwards and inwards, such as when reading or walking downstairs.
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Oculomotor nerve
The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that controls several eye movements and raises the eyelid. It originates in the midbrain of the brainstem, specifically from the oculomotor nucleus located within the midbrain of the brainstem, ventral to the cerebral aqueduct.
The oculomotor nerve has three main motor functions: innervation to the pupil and lens, innervation to the intrinsic eye muscles, and innervation to the majority of the extraocular muscles. These extraocular muscles include the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique. The superior rectus and inferior oblique muscles work together to pull the eye upward without rotating it. The oculomotor nerve also includes axons of type GSE, which innervate the skeletal muscles of the same extraocular muscles.
The oculomotor nerve has both somatic (voluntary) and autonomic (involuntary) fibers. Somatic functions of the oculomotor nerve include the elevation of the upper eyelid and coordination of eye muscles for visual tracking and gaze fixation. Autonomic functions include supplying the sphincter pupillae and ciliary muscles of the eye. The sphincter pupillae constricts the pupil, reducing the amount of light entering the eye, while the contraction of the ciliary muscles alters the curvature of the lens, allowing individuals to focus on near objects.
The oculomotor nerve plays a crucial role in several eye movements, including saccades, smooth pursuit, fixation, accommodation, vestibulo-ocular reflex, and optokinetic reflex. Saccades are rapid, jerky motions of the eye that typically occur when shifting gaze between objects. Smooth pursuit helps keep the eyes focused on a moving object, and fixation occurs when staring at an object. The vestibule-ocular reflex adjusts eye position during fast head movements, while the optokinetic reflex is responsible for tracking moving objects.
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Frequently asked questions
The superior rectus muscle, found at the top of the eye, controls the upward movement of the eye. The superior oblique muscle also contributes to the upward movement of the eyeball.
The superior rectus muscle is one of four recti muscles, which attach to the front half of the eye. The superior oblique muscle, on the other hand, takes an angular approach to the eyeball and attaches to the posterior surface of the sclera.
There are six extraocular muscles that enable the eyes to move in all directions of sight. Four rectus muscles and two oblique muscles work together to move the eye up and down, side to side, and control its rotation.
The eye muscles are controlled by three cranial nerves: the oculomotor nerve, the trochlear nerve, and the abducens nerve. The superior rectus muscle is controlled by the oculomotor nerve, while the superior oblique muscle is controlled by the trochlear nerve.
