Logan Steele
The human wink, or the blink of only one eye, is a form of body language. While blinking is automatic and serves to keep the eyes moist, winking is a conscious act of communication. The orbicularis oculi muscle, which circles the eyes, is the main muscle that controls the opening and closing of the eyelids. It is composed of orbital, palpebral, and deep palpebral parts, each with its own specific attachments. The orbital part draws the skin of the forehead and cheek towards the nose, while the palpebral part allows for finer control of the eyelids, pulling the upper eyelids down and raising the lower ones.
| Characteristics | Values |
|---|---|
| Name of muscle | Orbicularis oculi |
| Parts | Orbital, palpebral, deep palpebral |
| Muscle type | Facial muscle |
| Muscle function | Closes the eye |
| Controlled by | Facial nerve (Cranial nerve VII) |
| Muscle shape | Flat, broad and elliptical |
| Muscle location | Under the skin, around the circumference of the orbit |
| Muscle origin | Nasal part of frontal bone, frontal process of maxilla, medial palpebral ligament |
| Involuntary function | Protects the eye from irritants |
| Voluntary function | Used for winking and non-verbal communication |
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What You'll Learn
The orbicularis oculi muscle
Orbicularis oculi is composed of orbital, palpebral, and deep palpebral parts, each with its own specific attachments and functions. The orbital part overlays the orbital rim and originates from the nasal part of the frontal bone, frontal process of the maxilla, and medial palpebral ligament. The fibres encircle the orbit completely and extend into the soft tissues of adjacent regions. The orbital part has no bony insertions but attaches to various soft tissue structures of the periorbital region.
The palpebral part originates from the superficial surface of the medial palpebral ligament. The muscle fibres compose the eyelids as they travel towards the lateral commissure of the eye, where the superior and inferior fibres unite and insert into the lateral palpebral ligament (raphe). The palpebral part is crucial for voluntary and involuntary blinking and is subdivided into the preseptal, pretarsal, and ciliary sections.
The deep palpebral part, also known as the lacrimal part, originates from the lateral surface and lacrimal crest of the lacrimal bone. The fibres course laterally, passing posterior to the lacrimal sac. Some insert into the superior and inferior tarsi of the eyelids, while others continue past the tarsi to insert into the lateral palpebral ligament. The lacrimal part facilitates tear drainage and is involved in the protection of the eye.
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The levator palpebrae superioris muscle
The function of the levator palpebrae superioris muscle is to elevate and retract the upper eyelid, contributing to facial expressions of fear, anger, and shock. Its elevation of the upper eyelid also prevents obstruction of the pupil, ensuring an unhindered upward gaze.
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The palpebral part
The palpebral and orbital portions of the orbicularis oculi muscle can work independently of each other. For example, the orbital portion can contract to reduce glare, while the palpebral portion relaxes to keep the eyes open. Each time the eyelids are closed through the action of the orbicularis, the medial palpebral ligament is tightened, and the wall of the lacrimal sac is drawn forward and lateral, creating a vacuum that sucks tears into the lacrimal sac through the lacrimal canals.
The lacrimial part of the orbicularis oculi, also known as the deep palpebral part, originates from the lateral surface and lacrimal crest (superior part) of the lacrimal bone. The fibres course laterally, passing posterior to the lacrimal sac. Some insert into the superior and inferior tarsi of the eyelids, while others continue past the tarsi to insert into the lateral palpebral ligament. The lacrimal orbicularis facilitates the tear pump into the lacrimal sac.
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The Muller's muscle
The superior tarsal muscle, also known as Müller's muscle, is a smooth muscle that helps to raise the upper eyelid. It was first described by Müller in 1858 as a smooth muscle with many features of a striated muscle. It arises from the striated levator palpebrae superioris (LPS) muscle and extends to insert itself at the superior border of the tarsus.
Müller's muscle has a sympathetic innervation derived from the cervical sympathetic chain via third neuron fibres that pass from the carotid plexus. Its role is not yet fully understood, but it is believed to be an accessory muscle that helps to raise the upper eyelid. It may also serve to adjust the upper eyelid's position in response to changes in light intensity and pupil size. This hypothesis is known as the "eyelid-light reflex".
Isolated Müller's muscle resection is a surgical procedure that has been shown to be effective in correcting ptosis in patients with moderate to good levator function. The procedure involves the resection of Müller's muscle together with the overlying conjunctiva, and it has been found to improve eyelid contour and increase margin reflex distance.
Müller's muscle is also associated with the development of blepharoptosis, a condition characterised by drooping of the upper eyelid. This condition can occur due to damage to the sympathetic nervous system, which can inhibit the function of Müller's muscle, leading to a partial drooping of the eyelid.
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The superior oblique muscle
The function of the superior oblique muscle is to produce eye movements that direct the gaze down and out (inferolaterally) by abducting, depressing, and internally rotating the eye. It does not act in isolation but combines with other extraocular muscles. For example, the depression of the eye is usually the function of the inferior rectus muscle, but when the eye is adducted, the superior oblique muscle combines with the medial rectus to depress the eye.
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Frequently asked questions
The orbicularis oculi muscle is the main muscle that closes the eyelid during a wink. This flat, broad muscle forms an ellipse around the circumference of the eye.
The levator palpebrae superioris muscle opens the eye, while the inferior palpebral muscle and Müller's muscle (or superior tarsal muscle) in the upper eyelid are involved in widening the eyes.
Winking is harder than blinking because it involves the conscious control of a group of muscles that are normally triggered by autonomous reactions. A successful wink also involves some scrunching of the face, which can include the raising or lowering of the mouth.
