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The orbicularis oculi muscle is the main protractor muscle that closes the eyelid. It is a large, thin, circular muscle that is divided into three parts: the pretarsal, preseptal, and orbital segments. The eyelids also feature the levator palpebrae superioris muscle, which, with minor contributions from the frontalis and Muller's muscles, maintains the normal position of the upper eyelid.
| Characteristics | Values |
|---|---|
| Muscle that controls eyelid | Orbicularis oculi muscle |
| Location of the muscle | Beneath the eyelid skin |
| Function | Eyelid movement, opening and <co: 1,3,8,9,12,16,17,18,19>closing the eyelids, and facial expressions |
| Parts | Orbital, palpebral, lacrimal, and marginal |
| Innervation | Facial nerve (CN VII, temporal and zygomatic branches) |
| Attachments | Originates from the medial orbital margin, the medial palpebral ligament, and the lacrimal bone |
| Insertions | Inserts into the skin around the orbit's margin and the superior and inferior tarsal plates |
| Orbital portion | Subject to conscious control and responsible for forceful closure of the eyelids |
| Palpebral portion | Acts involuntarily, closing the eyelids gently during sleep or blinking |
| Marginal portion | Appears as a distinct line along the length of the upper and lower eyelid margins |
| Levator palpebrae superioris muscle | Maintains the normal position of the upper eyelid and raises the upper eyelid |
| Frontalis muscle | Assists in looking up and increasing vision in low light or when objects are far away |
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What You'll Learn
- The levator palpebrae superioris muscle raises the upper eyelid
- The orbicularis oculi muscle closes the eyelids
- The frontalis muscle pulls the eyebrows upward
- The M-group in the midbrain coordinates vertical eye movements and lid position
- The interstitial nucleus of Cajal inhibits the M-group neurons during downgaze, resulting in eyelid lowering
The levator palpebrae superioris muscle raises the upper eyelid
The levator palpebrae superioris muscle originates in the apex of the orbit and travels forward over the eyeball, attaching to the anterior surface and the superior edge of the superior tarsal plate. The superior tarsal plate, composed of dense connective tissue, forms the scaffolding of the upper eyelid and houses the Meibomian glands, which secrete an oily substance to slow the evaporation of the eye's tear film and prevent the eyelids from sticking together when closed.
The levator palpebrae superioris muscle is the direct antagonist of the orbicularis oculi muscle, which is responsible for closing the eyelids. The orbicularis oculi muscle is situated just beneath the eyelid skin and extends from the medial to the lateral canthal region, enhancing the structural integrity and functionality of the eyelids. It has both orbital and palpebral sections, with the orbital portion facilitating voluntary, forceful closure of the eyelids and the palpebral portion acting involuntarily to gently close the eyelids during sleep or blinking.
The orbicularis oculi muscle interacts with the nasolacrimal duct system to facilitate tear drainage. During blinking or eyelid closure, the preseptal and pretarsal parts of the palpebral orbicularis oculi contract, compressing the small channels that drain tears from the eye's surface to the lacrimal sac. This creates a vacuum effect, drawing tears into the lacrimal sac and facilitating their passage down the nasolacrimal duct toward the nasal cavity.
The levator palpebrae superioris muscle and the orbicularis oculi muscle work in coordination to maintain proper eyelid function, with the levator palpebrae superioris muscle raising the upper eyelid during wakefulness and the orbicularis oculi muscle gently closing the eyelids during sleep or blinking to protect and lubricate the eyes.
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The orbicularis oculi muscle closes the eyelids
The orbicularis oculi muscle, situated just beneath the skin of the eyelid, is crucial in eyelid movement. It extends from the medial to the lateral canthal region, enhancing the eyelid's structural integrity and functionality. The muscle is divided into three distinct parts: palpebral, lacrimal, and orbital. The palpebral part is responsible for the gentle closure of the eyelids, such as during sleep or blinking. The lacrimal part is involved in draining tears from the eyes. The orbital part is subject to conscious control and facilitates the voluntary, forceful closure of the eyelids.
The orbicularis oculi muscle interacts with the nasolacrimal duct system to facilitate tear drainage. During blinking or eyelid closure, the preseptal and pretarsal parts of the palpebral orbicularis oculi contract, compressing the small channels that drain tears from the eye's surface to the lacrimal sac. This action simultaneously pulls the lacrimal sac forward and creates a vacuum, drawing tears into the sac and ensuring their passage down the nasolacrimal duct toward the nasal cavity. The lacrimal part of the orbicularis oculi also helps to hold the eyelids together, keeping the lacrimal passage waterproof.
The orbital and palpebral portions of the orbicularis oculi muscle can work independently of each other. For example, the orbital portion can contract to furrow the brows and reduce glare, while the eyelids remain open due to the relaxation of the palpebral portion. The entire muscle is brought into action during forceful eyelid closure, such as in photophobia, resulting in the skin of the forehead, temple, and cheek being drawn toward the medial angle of the orbit.
The orbicularis oculi muscle is a facial expression muscle that may be affected by conditions such as Bell's palsy, resulting in the inability to blink or close the eyelid. Botulinum toxin injections target this muscle to smooth dynamic periorbital wrinkles. Understanding the anatomy and function of the orbicularis oculi muscle is essential in treating various eye and cosmetic conditions.
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The frontalis muscle pulls the eyebrows upward
The frontalis muscle is a pair of large, fan-like muscles that extend from the eyebrow region to the top of the forehead. It is the only muscle that raises the eyebrows, pulling them upward and causing horizontal wrinkles on the forehead when it contracts. This muscle is also responsible for conveying emotions and nonverbal communication. For example, expressions such as surprise, anger, joy, and concern can be demonstrated through the frontalis muscle without the need for words.
The frontalis muscle originates from the galea aponeurotica and inserts at the skin of the eyebrows and nose. The frontal nerve, a branch of the facial nerve, innervates the frontalis muscle. The orbicularis oculi muscles, which are located just under the skin and circle the eyes, intersect with the lateral aspect of the frontalis muscle. The corrugator and procerus muscles are also connected to the frontalis muscle.
The frontalis muscle is considered a weak retractor of the upper eyelids. When the frontalis muscle contracts, the vertical fibers pull the skin of the eyebrows upward, resulting in a maximum of 2 mm of elevation of the upper eyelid. This elevation of the brow can be important in maintaining the normal position of the upper eyelid, along with the levator palpebrae superioris muscle and Müller's muscle.
The frontalis muscle has no bony attachments, and its functionality is limited to raising the eyebrows and causing wrinkles in the forehead skin. Over time, repeated contractions of the frontalis muscle can lead to the formation of persistent horizontal wrinkles in the overlying skin, known as hyperfunctioning facial lines.
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The M-group in the midbrain coordinates vertical eye movements and lid position
The eyelids and the eyes work in tandem, with the eyelids moving with the eyes during both slow and rapid vertical eye movements. The major exception to this is when we blink, during which the eyelids close. The orbicularis oculi muscle, which circles the eyes, is responsible for eyelid closure. The muscle has three distinct 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 muscle, with minor contributions from Müller's and the frontalis muscles, maintains the normal position of the upper eyelid. The levator palpebrae superioris and superior tarsal muscles work together to open the eyelid. They are only present in the upper eyelid. The superior tarsus also acts as the attachment site of the levator palpebrae superioris.
Recent evidence suggests that the M-group in the midbrain coordinates vertical eye movements and lid position. The midbrain, or mesencephalon, is a complex structure with a range of different neuron clusters, neural pathways, and other structures. It is involved in several functions, including motor control, particularly eye movements, and the processing of vision and hearing. The M-group neurons excite the CCN (central caudal nucleus), causing the levator muscles to contract and the eyelids to open. During downgaze, neurons from the interstitial nucleus of Cajal (inC) inhibit the M-group neurons and the CCN, resulting in levator relaxation and eyelid lowering.
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The interstitial nucleus of Cajal inhibits the M-group neurons during downgaze, resulting in eyelid lowering
The eyelids are controlled by a combination of muscles and nerves. The levator palpebrae superioris muscle, with minor contributions from Müller's and the frontalis muscles, maintains the normal position of the upper eyelid. The orbicularis oculi muscle has three distinct parts – palpebral, lacrimal, and orbital – and is responsible for opening and closing the eyelids.
The exact nature of the cortical control of the eyelids is unclear, but evidence suggests that the right hemisphere may play a dominant role in this function. Vertical eye movements and lid position are coordinated through the M-group (supraoculomotor area or supra III) in the midbrain. During upgaze, M-group neurons excite the central caudal nucleus (CCN), causing the levator muscles to contract and the eyelids to open.
The interstitial nucleus of Cajal (INC) is a prominent group of cells within the medial longitudinal fasciculus of the brainstem. It is responsible for maintaining oculomotor control, head posture, and
The INC is essential in integrating velocity signals from the gaze control system into position signals when maintaining eye and head posture. The right INC encodes clockwise-up and clockwise-down eye and head movements, while the left INC encodes counterclockwise-up and counterclockwise-down movements. Lesions in this structure can result in nystagmus in upward or downward gaze.
During downgaze, neurons from the INC inhibit the M-group neurons and the CCN, resulting in levator relaxation and eyelid lowering. This inhibition of the M-group neurons during downgaze is a critical function that leads to the lowering of the eyelids.
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Frequently asked questions
The orbicularis oculi muscle is responsible for eyelid movement and closure.
The orbicularis oculi muscle has three distinct 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 levator palpebrae superioris muscle, along with the superior tarsal muscle, acts to open the eyelid. They are only present in the upper eyelid.
Auxiliary muscles such as the corrugator supercilii, procerus (pyramidalis), and frontalis muscles assist in cooperating with the eyelid muscles.
