Palpebral part of orbicularis oculi

At a glance

English

Palpebral part of orbicularis oculi

Latin (TA2)

Pars palpebralis musculi orbicularis oculi

System

Muscle

Region

Head

Side

Paired, left and right

About the palpebral part of orbicularis oculi

The orbicularis oculi is the circular muscle of the eyelids and the only muscle that can close the eye. Its palpebral part is the inner portion that lies within the lids themselves, under their very thin skin and in front of the orbital septum and tarsal plates. Compared with the thick, red orbital part around the rim of the orbit, it is thin and pale, and its fibres run in a series of curved arcs through the upper and lower lids. It is often described in two zones: a preseptal part over the orbital septum and a pretarsal part over the tarsus.

It springs from the medial palpebral ligament at the inner corner of the eye, where that ligament splits into upper and lower limbs, and from the bone just above and below it. The fibres curve outwards in concentric arcs, the upper set through the upper lid and the lower set through the lower lid, and meet at the outer corner of the eye in the lateral palpebral raphe, which is anchored by fibrous tissue to the zygomatic bone. The fibres nearest the lid margin, close to the lashes, form a fine bundle known as the ciliary part.

This part works mostly without conscious effort. It sweeps the lids together in the spontaneous blink, which is thought to depend chiefly on the pretarsal fibres, and holds them shut during sleep. Each blink spreads the tear film over the cornea and, by tightening the medial palpebral ligament and the deep lacrimal fibres, helps to draw tears through the lacrimal canaliculi into the sac. It can also relax while the orbital part contracts, so that the brows lower against glare while the eye stays open. Its direct antagonist is levator palpebrae superioris, which raises the upper lid.

Its motor supply is the facial nerve, through the temporal branches above and the zygomatic branches below; blood reaches it from the palpebral arcades of the ophthalmic and facial systems. The corneal reflex, a blink when the cornea is touched, tests this muscle together with the trigeminal nerve and can be checked even in an unconscious patient. When the facial nerve fails, the lids cannot close, the lower lid sags and tears spill over, and the cornea is at risk of drying and ulceration.

Attachments, action and supply

Origin

Medial palpebral ligament and the adjoining bone at the inner corner of the eye.

Insertion

Lateral palpebral raphe, at the eye's outer corner.

Action

Closes the eyelids gently, as in blinking and sleep, and assists the drainage of tears.

Nerve supply

Temporal and zygomatic branches of the facial nerve (cranial nerve VII).

Blood supply

Palpebral arterial arcades from the medial and lateral palpebral arteries, with branches of the facial artery.