Victor Forge
The human eyelid is a complex structure that plays a crucial role in protecting the eye and facilitating various functions such as blinking and winking. The movement of the eyelids is made possible by several muscles working in harmony. One of the key muscles involved in eyelid movement is the orbicularis oculi muscle, which is situated just beneath the eyelid skin. This muscle is responsible for closing the eyelids and assisting with tear drainage. It consists of three distinct parts: the palpebral, lacrimal, and orbital parts, each contributing to different aspects of eyelid function. In addition to the orbicularis oculi muscle, other muscles such as the levator palpebrae superioris and superior tarsal muscles are involved in opening the eyelid. These muscles work in coordination with vertical eye movements to ensure the eyelids open and close appropriately. Understanding the anatomy of these muscles is essential not only for cosmetic procedures but also for treating various eye conditions and maintaining ocular health.
| Characteristics | Values |
|---|---|
| Muscle name | Orbicularis oculi |
| Location | Under the eyelid skin |
| Function | Eyelid movement, tear drainage, facial expression |
| Parts | Orbital, palpebral, lacrimal |
| Innervation | Facial nerve (CN VII), temporal and zygomatic branches |
| Levator muscle | Levator palpebrae superioris |
| Levator function | Opens the eyelid |
| Levator innervation | Oculomotor nerve, sympathetic fibres |
| Superior tarsal muscle | Müller muscle |
| Superior tarsal innervation | Oculosympathetic neurons |
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What You'll Learn
The orbicularis oculi muscle
The orbital portion of the orbicularis oculi muscle is responsible for the forceful closure of the eyelids. It attaches to the anterior limb of the medial canthal tendon and connects to the lateral palpebral raphe. This section of the muscle interacts with neighbouring muscles, such as the frontalis, corrugator supercilii, and levator palpebrae superioris.
The palpebral part of the orbicularis oculi muscle is involved in both voluntary and involuntary blinking. It originates from the medial palpebral ligament and inserts into the lateral palpebral raphe at the outer corner of the eye. The palpebral portion consists of the preseptal, pretarsal, and ciliary sections. The preseptal and pretarsal sections play a role in tear drainage by compressing the small channels that drain tears from the eye's surface to the lacrimal sac.
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The levator palpebrae superioris muscle
The levator palpebrae superioris is attached to the check ligament of the superior rectus muscle, and these two muscles contract simultaneously. The levator palpebrae superioris is also connected to the superior tarsal muscle (Müller muscle), a small slip of smooth muscle that attaches to the underside of the levator palpebrae superioris near its insertion point. The superior tarsal muscle is a component of the levator palpebrae superioris according to some authors.
The levator palpebrae superioris receives its blood supply from the ophthalmic and supraorbital arteries, which are branches of the internal carotid artery. The muscle is innervated by the superior branch of the oculomotor nerve (CN III), a cranial nerve that originates in the midbrain. The levator palpebrae superioris is a skeletal muscle, not a smooth muscle.
The levator palpebrae superioris is associated with the Whitnall ligament and levator aponeurosis. The levator aponeurosis inserts into the upper eyelid skin and the upper tarsal plate's anterior surface. The Whitnall ligament is a transverse suspensory ligament that is part of the orbital pulley system, facilitating the transition of the horizontally oriented levator palpebrae superioris into the vertical levator aponeurosis.
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The superior tarsal muscle
The main function of the superior tarsal muscle is to elevate the upper eyelid, particularly in states of sympathetic predominance such as excitement, fear, or surprise. This action enables a wider visual field in acute life-threatening situations, triggering a fight or flight response. In addition to elevating the eyelid, the static tone of the muscle also contributes to maintaining the eyes open and keeping the size of the palpebral fissure constant during wakefulness.
Damage to certain elements of the sympathetic nervous system can impair the function of the superior tarsal muscle, leading to a condition known as partial ptosis, characterised by a drooping eyelid. Horner's syndrome, a similar condition, presents with a triad of symptoms, including partial ptosis, miosis (constricted pupil), and loss of hemifacial sweating (anhidrosis).
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The palpebral, lacrimal and orbital parts of the orbicularis oculi
The orbicularis oculi muscle is a sphincter-like muscle that surrounds the eyes and is located just under the skin of the eyelids. It is responsible for eyelid movement and plays a crucial role in facial expressions. The muscle is divided into three parts: the palpebral, lacrimal, and orbital parts, each with distinct functions and anatomical characteristics.
The palpebral part of the orbicularis oculi muscle is responsible for gently closing the eyelids. It arises from the bifurcation of the medial palpebral ligament and forms a series of concentric curves. This portion of the muscle contains the preseptal and pretarsal muscles, with the latter believed to be responsible for the spontaneous blink. The palpebral part has thinner fibres that continue seamlessly into the orbital part.
The lacrimal part of the orbicularis oculi is involved in tear drainage. It is a small, thin muscle situated behind the medial palpebral ligament and lacrimal sac. This muscle originates from the posterior crest and adjacent parts of the orbital surface of the lacrimal bone. It then divides into two slips, upper and lower, which insert into the superior and inferior tarsi medial to the puncta lacrimalia. The lacrimal part facilitates the tear pump into the lacrimal sac, drawing the eyelids and ends of the lacrimal canals medialward, and compressing them against the surface of the globe of the eye.
The orbital part of the orbicularis oculi is responsible for the forceful closure of the eyelids. It is thicker and reddish in colour, forming a complete ellipse without interruption at the lateral palpebral commissure. The orbital portion forms the bulk of the muscle and can squeeze the eyelids shut tightly. It attaches to the anterior limb of the medial canthal tendon and the surrounding periosteum medially, while connecting to the lateral palpebral raphe laterally. The orbital part interdigitates with neighbouring muscles, such as the frontalis muscle, making it integral to facial expressions.
The orbicularis oculi muscle as a whole is innervated by the seventh cranial nerve, also known as the facial nerve or cranial nerve VII. It exhibits a predominantly type II (fast-twitch) fibre composition, enabling rapid and protective eyelid movements. This muscle is essential not only for eyelid movement but also for maintaining ocular health and conveying non-verbal messages through winks.
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The role of eyelid muscles in facial expressions
The eyelids are moved by a combination of muscles, including the levator palpebrae superioris, superior tarsal, orbicularis oculi, and Muller's muscle. The eyelids are also influenced by the muscles that move the eyeball, known as extraocular muscles, which include the medial rectus, lateral rectus, inferior and superior oblique, and inferior and superior rectus muscles.
The role of these eyelid muscles in facial expressions is significant, particularly in the case of the orbicularis oculi muscle. This muscle is situated just beneath the eyelid skin and is responsible for eyelid movement, including the opening and closing of the eyelids. It is divided into three parts: palpebral, lacrimal, and orbital. The palpebral part gently closes the eyelids, the lacrimal part is involved in tear drainage, and the orbital part tightly closes the eyelids. The palpebral portion also plays a role in winking and blinking.
The orbicularis oculi muscle is a facial expression muscle that contracts and relaxes, causing the skin over it to move. It is attached to the skin through fibre tissues that form the superficial musculoaponeurotic system. This muscle consists of two main parts: the orbital part and the palpebral portion. The orbital part is further divided into pretarsal and preseptal segments and is responsible for tightly shutting the eyelids. The palpebral portion, as mentioned earlier, is involved in blinking and winking.
The orbital part of the orbicularis oculi muscle has a close relationship with other muscles responsible for facial expressions. It is innervated by the facial nerve (CN VII) and its branches, including the temporal and zygomatic branches. The facial nerve supplies the muscle by travelling under it and sending different branches to the various sections of the muscle.
The levator palpebrae superioris muscle is also involved in eyelid movement, specifically in the elevation of the upper eyelid. It is innervated by the oculomotor nerve (CN III) and its superior branch directly influences the levator palpebrae superioris and the superior rectus muscles, allowing synchronous upper eyelid elevation during upward gaze.
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Frequently asked questions
The orbicularis oculi muscle is responsible for closing the eyelids. It has three parts: palpebral, lacrimal, and orbital. The palpebral part gently closes the eyelids, the lacrimal part is involved in draining tears, and the orbital part tightly closes the eyelids.
The levator palpebrae superioris and superior tarsal muscles open the eyelid. They are only present in the upper eyelid.
The orbicularis oculi muscle is a thin layer of muscle situated just beneath the eyelid skin. It circles the eyes and is divided into orbital and palpebral sections, each with specific functions. The orbital part is involved in tightly shutting the eyelids, while the palpebral part plays a role in blinking and winking.
The superior tarsal muscle (also known as Müller's muscle) is a smooth muscle that attaches to the superior tarsal plate. It is innervated by oculosympathetic neurons. The levator palpebrae superioris muscle is also involved in eyelid movement, receiving innervation from the oculomotor nerve (CN III).
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