The muscles of facial expression, are generally localized around the facial orifices, and their contraction leads to changes in facial expression such as when smiling, laughing, frowning, grimacing or squinting etc .
The orbicularis oculi muscle belongs to the orbital group of the muscles of facial expression. This muscle encircles the orbit and is a primary sphincter muscle. It is comprised of three parts: the orbital part, the palpebral part and the lacrimal part.
These three parts of the orbicularis oculi muscle all have different points of origin and insertion.
The orbital part of the muscle has its origins on the frontal process of the maxilla, the nasal part of the frontal bone and the medial palpebral ligament. The fibers of the orbital part of this muscle, encircle the eye as an uninterrupted loop and insert around the orbit.
The palpebral part of orbicularis oculi arises from the medial palpebral ligament and inserts on the lateral palpebral raphae. This part of the orbicularis oculi muscle is not as broad as the orbital part, however, it does surround the lacrimal part of the muscle.
Finally, the lacrimal part of the orbicularis oculi muscle has its origin on the lacrimal bone and inserts on the lacrimal fascia around the lacrimal canaliculi.
In addition to having different points of origin and insertion, the three parts of the orbicularis oculi muscle also perform different functions. The orbital part of the muscle facilitates the forcible closure of the eyelids, while the palpebral part is responsible for the gentle closure of the eyelids, for example during blinking. The lacrimal part of this muscle aids or supports the flow of tear fluid.
The orbicularis oculi muscle is innervated by the temporal and zygomatic branches of the facial nerve (CN VII).
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