Muscles of facial expression

Topography of facial muscles in the buccal region

The buccal region has a distinct layered structure. Facial muscles lie in the second layer—within the loose subcutaneous adipose tissue, which also contains the initial segment of the facial artery (a. facialis).

The main representative of the facial musculature here is the buccinator muscle (m. buccinator). Partially located in this same zone are:

• zygomaticus major and minor muscles;
• risorius muscle;
• levator anguli oris muscle.

Externally, the buccinator muscle is covered by the dense buccopharyngeal fascia (fascia buccopharyngea). Deeper lies the buccal fat pad (Bichat's fat pad), enclosed in its own capsule. The parotid duct (ductus parotideus) pierces its path through the buccinator muscle and the fat pad. It opens onto the mucous membrane of the oral vestibule at the level of the second upper molar. The duct is accompanied by the buccal branches of the facial nerve and the transverse facial artery.

Features of the infraorbital region

The infraorbital region (regio infraorbitalis) is bounded superiorly by the infraorbital margin, medially by the lateral nasal wall, inferiorly by the alveolar process of the maxilla, and laterally by the zygomaticomaxillary suture.

Here, facial muscles attach directly to the anterior wall of the maxilla. A crucial anatomical feature is that each muscle is surrounded by a loose fascial sheath. Intercommunicating layers of adipose tissue lie between these muscle sheaths.

Clinical significance: This structure explains the development of significant soft tissue edema during purulent-inflammatory processes. Infection (often odontogenic, originating from the upper incisors, canines, or premolars) can easily spread through the adipose tissue. From the canine fossa, where the nasolabial lymph node is located, pus can penetrate into the orbit via the infraorbital canal. Involvement of the facial and angular veins creates a risk of severe intracranial complications, such as cavernous sinus thrombosis or meningitis.

Innervation and cortical representation (Penfield's Homunculus)

Motor activity of the facial muscles is entirely controlled by the facial nerve (n. facialis, cranial nerve VII). Sensory innervation of the overlying skin is provided by branches of the trigeminal nerve (n. trigeminus, cranial nerve V): the ophthalmic, maxillary, and mandibular nerves.

In the cerebral cortex, a colossal area is allotted to the facial muscles, as described by the concept of "Penfield's Homunculus". The core principle of this somatotopic organization is that the size of the cortical area is proportional not to the physical size of the body part, but to its functional significance.

1. In the primary motor cortex (precentral gyrus), the head and face region occupies a vast territory. This is necessary to ensure highly complex, finely coordinated motor acts: emotional expression, articulation, chewing, and phonation.
2. In the primary somatosensory cortex (postcentral gyrus), the face, lips, and mouth also have an extensive representation due to the highest density of receptors and maximal tactile sensitivity.

Class and exam questions

What else to study on this topic

• Layered topography of the buccal region and anatomy of the buccal fat pad (Bichat's fat pad).
• Topography and path of the parotid duct.
• Zones of sensory innervation of the head and neck (branches of the trigeminal nerve and cervical plexus).
• Pathways of spread of odontogenic infection from the infraorbital region into the cranial cavity.
• Somatotopic organization of the cerebral cortex (Sensory and Motor Homunculus).

Other topics in the "Additional Topics" section

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