Victor Forge
The oculomotor nerve (CN III) is one of three cranial nerves that directly innervate the six extraocular muscles, which are responsible for eye movement. These muscles include the internal rectus, superior rectus, and inferior oblique, as well as the levator palpebrae superioris (LPS), which is the only muscle involved in raising the upper eyelid. The orbicularis oculi muscle is a paired facial muscle that surrounds each orbit and the adjacent periorbital region, forming an ellipse around the circumference of the orbit.
| Characteristics | Values |
|---|---|
| Name | Orbicularis oculi |
| Description | A paired facial muscle that surrounds each orbit and the adjacent periorbital region |
| Shape | Flat and broad, forming an ellipse around the circumference of the orbit |
| Composition | Orbital, palpebral and deep palpebral parts |
| Orbital part origin | Nasal part of frontal bone, frontal process of maxilla and medial palpebral ligament |
| Orbital part attachments | No bony insertions; attaches to soft tissue structures of the periorbital region, including skin and subcutaneous tissue of the eyebrow |
| Orbital part connections | Occipitofrontalis, corrugator supercilii, depressor supercilii, levator labii superioris, levator nasolabialis, and zygomaticus minor muscles |
| Deep palpebral part origin | Lateral surface and lacrimal crest (superior part) of lacrimal bone |
| Deep palpebral part attachments | Superior and inferior tarsi of eyelids, lateral palpebral ligament |
| Deep palpebral part connections | Corrugator supercilii, malaris muscle, levator palpebrae superioris |
| Innervation | Zygomatic and temporal branches of the facial nerve (cranial nerve VII) |
| Arterial blood supply | Maxillary, superficial temporal and facial arteries (branches of the external carotid artery); ophthalmic artery (branch of the internal carotid artery) |
| Function | Involved in facial expression, ocular protection, and reflexes; contraction can partially or completely close the eyelids to protect from bright light or blowing dust |
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What You'll Learn
The Orbicularis oculi muscle
The palpebral part of the Orbicularis oculi muscle is pierced by the levator palpebrae superioris (LPS) muscle, which is the only muscle involved in raising the superior eyelid. The LPS originates from the lesser wing of the sphenoid bone, immediately above the optic foramen, and attaches to the superior tarsal plate of the upper eyelid.
The deep palpebral part of the Orbicularis oculi muscle, or the lacrimal part, originates from the lateral surface and lacrimal crest (superior part) of the lacrimal bone. Its 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.
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The oculomotor nerve
The levator palpebrae superioris (LPS) muscle, responsible for raising the superior eyelid, is innervated by the oculomotor nerve. Additionally, the oculomotor nerve is involved in the abduction of the eyeball and contributes to adduction and medial rotation.
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Extraocular muscles
The extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. They are located within the orbit but are extrinsic and separate from the eyeball itself. They act to control the movements of the eyeball and the superior eyelid. The extraocular muscles are innervated by three cranial nerves. Damage to one of the cranial nerves will cause paralysis of its respective muscles and alter the resting gaze of the affected eye.
The six muscles responsible for eye movement are the four recti (straight) muscles and the two oblique muscles. The four recti muscles are named according to their relative positions of attachment: the superior rectus muscle, lateral rectus muscle, medial rectus muscle, and inferior rectus muscle. The two oblique muscles are the inferior oblique muscle and the superior oblique muscle. The movements of the extraocular muscles take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit.
The seventh extraocular muscle, the levator palpebrae superioris, is responsible for raising the upper eyelid. This can be a voluntary or involuntary action. The levator palpebrae superioris is the only muscle involved in raising the superior eyelid.
The extraocular muscles have a large ratio of nerve fibres to skeletal muscle fibres. They are a specialised skeletal muscle form with various fibre types, including slow tonic types, which resist fatigue, and saccadic (rapid) muscle fibres.
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Superior eyelid muscles
The superior eyelid is maintained in its normal position by the levator palpebrae superioris muscle, with minor contributions from the frontalis and Müller's muscles. The levator palpebrae superioris muscle is an extraocular muscle innervated by the oculomotor nerve (CN III). The contraction of this muscle draws the superior eyelid upward. Paralysis of this muscle leads to a condition called ptosis, where a person is unable to elevate their upper eyelid. The levator palpebrae superioris muscle is attached to the anterior surface and the superior edge of the superior tarsal plate. The tarsal plates are composed of dense connective tissue and form the scaffolding of the eyelid. The superior tarsal muscle (Müller's muscle) is an accessory smooth muscle that provides additional lift to the eyelid beyond what is achieved by the contraction of the levator palpebrae superioris.
The orbicularis oculi muscle is a paired facial muscle that surrounds each orbit and the adjacent periorbital region. It is a muscle of facial expression and is involved in ocular protection and reflexes. It is innervated by the zygomatic and temporal branches of the facial nerve (CN VII). The contraction of the orbital part of the orbicularis oculi muscle draws the skin of the forehead and cheek towards the nose. This protective function can partially or completely close the eyelids, limiting exposure to potential damaging factors such as bright light or blowing dust. 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 the drainage of tears, and the orbital part tightly closes the eyelids.
The superior eyelid muscles and their innervations are important for maintaining the position and function of the upper eyelid. The levator palpebrae superioris muscle is the primary muscle responsible for elevating the upper eyelid, with assistance from the superior tarsal muscle (Müller's muscle). The frontalis muscle also contributes to the maintenance of the normal position of the upper eyelid. The innervation of these muscles is crucial for their proper function. The levator palpebrae superioris muscle is innervated by the oculomotor nerve (CN III), the superior tarsal muscle by oculosympathetic neurons, and the frontalis muscle by the facial nerve.
The orbicularis oculi muscle also plays a significant role in the superior eyelid. It is involved in facial expression and ocular protection. The contraction of the orbital part of this muscle helps to close the eyelids, protecting the eyes from potential damage. The palpebral and lacrimal parts of the orbicularis oculi muscle are also involved in eyelid closure and tear drainage, respectively. The innervation of the orbicularis oculi muscle is provided by the zygomatic and temporal branches of the facial nerve (CN VII).
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The orbital region
The palpebral part, also known as the orbitalis oculi, originates from the frontal bone and maxilla and inserts into the eyelids. The deep palpebral part, or lacrimal part, originates from the lateral surface and lacrimal crest of the lacrimal bone. Its fibres pass posteriorly to the lacrimal sac, with some inserting into the superior and inferior tarsi of the eyelids and others continuing past the tarsi to insert into the lateral palpebral ligament.
The orbicularis oculi is pierced by two major neurovasculature structures: the supraorbital vein and the zygomaticofacial nerve. It is innervated by the zygomatic and temporal branches of the facial nerve (cranial nerve VII) and receives arterial blood from three branches of the external carotid artery: the maxillary, superficial temporal, and facial arteries. The ophthalmic artery, a branch of the internal carotid artery, also supplies the muscle.
The orbicularis oculi is considered the sphincter of the eyelids and is involved in facial expression, ocular protection, and reflexes. Contraction of the orbital part draws the skin of the forehead and cheek towards the nose, providing a protective function that can partially or completely close the eyelids to limit exposure to potential damage from bright light or blowing dust.
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Frequently asked questions
The oculo-motor nerve is one of the three cranial nerves that directly innervate the three pairs of extra-ocular muscles that move the eyeball.
Extra-ocular muscles are the six muscles (excluding the levator) that are attached to the globe and control the eyeball.
The orbicularis oculi muscle is a paired facial muscle that surrounds each orbit and the adjacent periorbital region. It is considered the sphincter of the eyelids and is involved in facial expression, ocular protection and reflexes.
The LPS is the only muscle involved in raising the superior eyelid. It originates from the lesser wing of the sphenoid bone and attaches to the superior tarsal plate of the upper eyelid.
The oculomotor nerve (CN III) is involved in the innervation of the extra-ocular muscles. A lesion of the oculomotor nerve affects most of the extra-ocular muscles, causing the affected eye to be displaced laterally and inferiorly.
