Orbicularis oris muscle

Location and anatomy

The orbicularis oris muscle is part of the muscular layer of the lips. The lips form the anterior wall of the oral cavity, and their free margins border the oral fissure and form the angles of the mouth (anguli oris).

Topography of the lips (layered structure from outside to inside):

• Skin — thin, contains numerous sebaceous and sweat glands. The skin is fused with the orbicularis oris muscle, making it relatively immobile.
• Red vermilion border — transitional zone.
• Mucous membrane — continuous with the buccal mucosa laterally and the gingival mucosa superiorly and inferiorly. In the midline, it forms the frenulum of the upper and lower lip.
• Submucosa — loose connective tissue. Contains mucous glands, superior and inferior labial arteries, veins, and nerves.
• Muscular layer — orbicularis oris muscle (m. orbicularis oris).

What is its function?

The orbicularis oris muscle performs the following functions:

• Closes the lips.
• Protrudes the lips forward, forming a "pout".
• Participates in facial expression: the muscle tightens when smiling.
• Helps maintain oral seal integrity; impairment may lead to drooling.
• Damage to the lips impairs the pronunciation of labial sounds.

Blood supply and innervation

• Blood supply: provided by branches of the facial artery (a. facialis), specifically the superior and inferior labial arteries (aa. labiales superiores et inferiores) and the angular artery (a. angularis). Additional blood supply comes from the infraorbital (a. infraorbitalis), mental (a. mentalis), and buccal (a. buccalis) arteries.
• Innervation: the muscle is innervated by the facial nerve (n. facialis). These facial muscles are supplied by rr. buccales, rr. zygomatici, and r. marginalis mandibulae.
• Central regulation: central motor neurons responsible for voluntary movements of facial muscles are located in the lower part of the precentral gyrus.

Clinical significance in surgery and orthodontics

• Traumatology: a deep wound of the lower lip involving the muscular layer presents with marked wound gaping. This is caused by the transection and retraction of m. orbicularis oris fibers.
• Reconstructive surgery: during lower lip reconstruction using a Filatov tube flap, a lip created solely from the flap sags and fails to provide an oral seal. To restore mobility, N. M. Michelson's technique is used: the orbicularis oris muscle of the upper lip is split longitudinally into two parts, and the lower part is implanted into the adipose tissue of the lower lip constructed from the Filatov flap.
• Orthodontics: preventive appliances, including preorthodontic trainers and Hinter's plates, normalize lip closure and strengthen the orbicularis oris muscle, providing myofunctional training.
• Congenital anomalies: in double lip, which represents hypertrophy of the mucous membrane, submucosa, and mucous glands, the pathology becomes apparent during speech and especially smiling: the orbicularis oris muscle tightens, causing the excess submucosa to protrude outward.

Neurological diagnosis

Contraction of the orbicularis oris muscle forms the basis of the snout reflex, which belongs to the primitive oral reflexes.

A light tap with a neurological hammer on the upper lip causes the lips to pucker due to the contraction of m. orbicularis oris. These reflexes indicate disinhibition of subcortical structures and are characteristic of pseudobulbar syndrome.

Pseudobulbar paralysis occurs due to lesions of the corticonuclear pathways. Possible lesion localizations: pons, bilateral subcortical basal ganglia, and bilateral frontal lobes.

Class and exam questions

What else to study on this topic

• Facial nerve (n. facialis) and its branches
• Topographic anatomy of the lips and oral cavity
• Muscles of facial expression
• Blood supply of the maxillofacial region

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.