Location and borders
The orbicularis oculi muscle belongs to the facial expression muscles, which develop from the 2nd pharyngeal arch. It is located superficially and has the following topographical features:
- In the structure of the eyelids: The muscle is located between the skin and the tarsal plate (eyelid cartilage). Circular bundles of the muscle run near the margin of both the upper and lower eyelids.
- Relation to other muscles: The inferior part of the orbicularis oculi lies most superficially. Beneath it lie the zygomaticus minor and major muscles (mm. zygomatici minor et major), which cover the levator labii superioris muscle (m. levator labii superioris).
What parts does it consist of?
Anatomically and functionally, the muscle is divided into three parts:
- Palpebral part (pars palpebralis) — participates in blinking.
- Orbital part (pars orbitalis) — participates in forceful eyelid closure.
- Lacrimal part (pars lacrimalis) — dilates the lacrimal sac upon contraction.
Blood supply and innervation
- Innervation: Supplied by the facial nerve (n. facialis, CN VII). The zygomatic branch (r. zygomaticus) approaches the muscle, running in the subcutaneous tissue over the anterior third of the zygomatic arch.
- Blood supply: The muscle is supplied by the supratrochlear (a. supratrochlearis), supraorbital (a. supraorbitalis), and angular (a. angularis) arteries. The frontal branch of the superficial temporal artery (r. frontalis a. temporalis superficialis) also participates in its blood supply.
Involvement in reflex arcs
The orbicularis oculi muscle serves as the efferent, effector component of protective reflexes:
- Corneal reflex: Normally, touching the cornea causes both eyes to close. The afferent signal travels from the ocular mucosa via the ophthalmic nerve (V1 branch of the trigeminal nerve) to the pontine nucleus. From there, the impulse is relayed to the facial nerve nucleus, which causes bilateral contraction of the orbicularis oculi muscle.
- Blink reflex: Rapid closure of the eyes in response to strong visual stimuli. The signal descends from the superior colliculi via the tectospinal/tectobulbar tract to the motor nucleus of the facial nerve, causing muscle contraction.
Clinical significance
- Facial nerve palsy: Leads to facial asymmetry and the development of lagophthalmos — the inability to completely close the eyelids due to impaired function of the orbicularis oculi muscle. This also leads to the loss of the corneal reflex.
- Trigeminal neuralgia: During a severe episode of facial pain, a painful tic (tic douloureux) may occur — a reflex contraction of the facial expression muscles on the affected side. The orbicularis oculi muscle is frequently involved in this process.
Class and exam questions
Which muscle prevents eye closure in facial nerve palsy?
In facial nerve palsy, the function of the orbicularis oculi muscle (m. orbicularis oculi) is impaired. This leads to the development of lagophthalmos — the inability to completely close the eyelids on the affected side.
How does the orbicularis oculi muscle participate in the corneal reflex?
It acts as the efferent, effector component. When the cornea is touched, the signal travels via the trigeminal nerve to the brainstem, is relayed to the facial nerve nucleus, which causes bilateral contraction of the orbicularis oculi muscle.
Which arteries supply the orbicularis oculi muscle?
Blood supply is provided by the supratrochlear (a. supratrochlearis), supraorbital (a. supraorbitalis), and angular (a. angularis) arteries, as well as the frontal branch of the superficial temporal artery.
What else to study on this topic
- Facial nerve (n. facialis) and its branches
- Structure of the eyelids and conjunctiva
- Corneal and blink reflexes
- Muscles of facial expression
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