Alec Titan
The human eye is a complex organ that relies on several muscles to function. These muscles are responsible for eye movement and position, as well as focusing and controlling how much light enters the eye. There are two types of eye muscles: extrinsic and intrinsic. The extrinsic muscles, also known as extraocular muscles, control eye movement and position. They are attached to the outside of the eyeball and enable the eyes to move in all directions. On the other hand, intrinsic muscles control near focusing and how much light enters the eye. This article will focus on the extrinsic muscles and their role in eye elevation.
| Characteristics | Values |
|---|---|
| Number of eye muscles | 6 extrinsic muscles and 1 muscle controlling the upper eyelid |
| Types | Extrinsic (external) and Intrinsic |
| Function of extrinsic muscles | Control eye movement and position |
| Function of intrinsic muscles | Control near focusing and how much light enters the eye |
| Types of extrinsic muscles | Rectus (4) and Oblique (2) |
| Function of rectus muscles | Control horizontal movement of the eye |
| Function of oblique muscles | Control vertical and torsional movement of the eye |
| Superior rectus | Controls upward movement of the eye |
| Inferior rectus | Controls downward movement of the eye |
| Medial rectus | Controls movement of the eye towards the nose (adduction) |
| Lateral rectus | Controls movement of the eye away from the nose (abduction) |
| Superior oblique | Depresses, abducts, and medially rotates the eyeball |
| Inferior oblique | Elevates, abducts, and rotates the eye |
| Muscle controlling the upper eyelid | Levator palpebrae superioris (LPS) |
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What You'll Learn
The superior rectus elevates the eye
The superior rectus is one of the four rectus muscles, which also include the medial rectus, the lateral rectus, and the inferior rectus. The superior rectus is also one of the seven extraocular muscles, which are located within the orbit but are extrinsic and separate from the eyeball itself. These muscles control the movements of the eyeball and the superior eyelid.
The superior rectus muscle is innervated by the superior division of the oculomotor nerve (CN III). In the primary position (looking straight ahead), its main function is to elevate the eye, causing the cornea to move superiorly. It also contributes to intorsion and adduction. The superior rectus originates from the annulus of Zinn and courses anteriorly and superiorly over the globe, making an angle of 23 degrees with the visual axis.
The extraocular muscles have a functional insertion point, which is the closest point where the muscle first contacts the globe. This point forms a tangential line from the globe to the muscle origin and is known as the arc of contact. The superior rectus has an arc of contact of 6.5 mm, which is also the same as the inferior rectus.
The superior rectus muscle is associated with a number of medical conditions. It may be weak, paralysed, or overreactive, and in some cases, it may even be congenitally absent. Treatment for an overreactive superior rectus may involve eye surgery to weaken or reposition the muscle, which generally has good outcomes.
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The inferior oblique elevates the eye
The human eye is a complex organ that relies on various muscles to function properly. One of these muscles is the inferior oblique, which plays a crucial role in eye movement and vision.
The inferior oblique is an extraocular muscle, meaning it is located within the orbit but is extrinsic and separate from the eyeball itself. It is one of six extraocular muscles that control eye movements, and it is unique in that it does not originate from the apex of the orbit. Instead, it arises from the medial orbital surface of the maxilla, just lateral to the nasolacrimal fossa. From there, it ascends obliquely and posterolaterally, coursing between the lateral rectus muscle and the floor of the orbit.
The primary function of the inferior oblique muscle is to externally rotate the eye. However, it also plays a significant role in elevating the eye. This elevation occurs when the eye is adducted, or turned inward, by the medial rectus muscle. In this position, the optical axis of the eye aligns with the orbital axis, and the inferior oblique produces ocular elevation. This movement is crucial for tasks such as looking up from reading, where the eyes need to move from a state of convergence.
The inferior oblique muscle works in synergy with other muscles, such as the superior rectus muscle, to elevate the pupil. At the same time, their rotatory actions oppose and neutralize each other, ensuring that no rotation of the eyeball occurs during its elevation. This complementary action is essential for maintaining proper eye alignment during elevation.
Any injury or dysfunction of the inferior oblique muscle can have significant consequences on eye movement and vision. Overaction or underaction of this muscle can lead to vertical strabismus, a condition characterized by misalignment of the eyes. Surgical intervention is often required to correct this movement disability, both for cosmetic and functional purposes.
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The levator palpebrae superioris elevates the eyelid
The levator palpebrae superioris is a skeletal muscle of the face that elevates the upper eyelid. It is the only muscle involved in raising the superior eyelid. It is one of the six extraocular muscles in the orbit. Extraocular muscles are located within the orbit but are separate from the eyeball itself. They control the movements of the eyeball and the superior eyelid.
The levator palpebrae superioris originates from the inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen. It broadens and decreases in thickness, becoming the levator aponeurosis. This portion inserts on the skin of the upper eyelid, as well as the superior tarsal plate. The levator palpebrae superioris receives its blood supply from branches of the ophthalmic artery, specifically, muscular branches and the supraorbital artery.
The main actions of the levator palpebrae superioris are the retraction and elevation of the superior eyelid and widening of the palpebral fissure. These actions are limited by several anatomical features of the muscle. For example, the orbital septum, a fibrous part of the eyelid, prevents further retraction of the eyelid when maximally compressed. Additionally, the orbicularis oculi counteracts the levator palpebrae superioris by pulling the eyelid in the opposite direction.
The levator palpebrae superioris is innervated by the sympathetic nervous system. It is controlled by the oculomotor nerve (CN III). Damage to this muscle or its innervation can cause ptosis, or drooping of the eyelid. Ptosis may also be indicative of sympathetic nerve damage in nearby muscles, such as the superior tarsal muscle.
To strengthen the levator palpebrae superioris and relieve bothersome eyelid twitching, targeted eyelid exercises can be performed daily. These include closing the eyelids tightly and holding this position for ten seconds, then opening the eyes as wide as possible and holding for another ten seconds.
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The superior oblique is involved in eye elevation
The superior oblique muscle is one of the two oblique extraocular muscles, which are extrinsic muscles that control eye movement and position. The superior oblique muscle is the longest of the six extrinsic muscles of the eye, which include the superior rectus, lateral rectus, inferior rectus, medial rectus, and inferior oblique muscles.
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. It then runs anteriorly, parallel to the medial wall of the orbit, and inserts into the sclera on the posterotemporal surface of the eyeball. The muscle tendon hooks around a cartilaginous pulley, called the trochlea of superior oblique, which is attached to the nasal part of the frontal bone.
The primary function of the superior oblique muscle is intorsion, or internal rotation, of the eye. It also depresses, abducts, and medially rotates the eyeball, directing the gaze inferolaterally (down and out). This unique path of the superior oblique muscle allows the eye to move down and out, preventing undesired rotatory actions of the inferior and superior recti about the long axis of the eye. The muscle is innervated by 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 involved in eye elevation, although its main action is depression of the eyeball. When the eye is abducted (looking laterally), the contribution of the superior oblique to depression decreases, as the inferior rectus muscle causes this movement more directly and powerfully. However, the superior oblique does contribute to a downwards and lateral eye movement. During neurological examinations, the depressing action of the superior oblique is tested by having the patient look inwards and downwards.
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The oculomotor nerve controls eye elevation
The oculomotor nerve, also known as Cranial Nerve III (CN III), is one of three nerves that control the muscles responsible for eye movement. It is a key component of vision, carrying command signals to the muscles that move the eye and its components. The oculomotor nerve controls the movement of the superior rectus muscle, which is found at the top of the eye and controls upward movement.
The oculomotor nerve also controls the movement of the inferior oblique muscle, which elevates the eye when it is adducted from its primary position. This muscle originates from the front of the orbital floor, close to the nose, and its main function is to extort the eye when looking straight ahead. It also elevates and abducts the eye, moving the direction of gaze upward and outward.
The oculomotor nerve has two main functions. Firstly, it constricts the pupil (miosis) by innervating the smooth muscle (sphincter pupillae) near the pupil. Secondly, it innervates the ciliary muscles, which connect the iris to the choroid. The contraction of the muscle alters the curvature of the lens, allowing the eye to focus on near objects.
The oculomotor nerve is one of the main nerves used to control how the eyes move. Its branches connect to muscles on multiple sides of the eyeballs, delivering movement commands from the brain to those muscles. The nerve helps to adjust and coordinate eye position during movement, including saccades, smooth pursuit, fixation, accommodation, vestibulo-ocular reflex, and optokinetic reflex.
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Frequently asked questions
The levator palpebrae superioris (LPS) is the muscle that raises the upper eyelid and keeps it in position.
The LPS is an extrinsic or extraocular muscle.
There are six extraocular muscles: four rectus muscles and two oblique muscles.
The superior rectus muscle controls upward movement of the eye.
