Lips--Anatomy and Function

 Updated 3/2017 -- photos and all links removed as many no longer active and it was easier than checking each one.

Our lips are very important in many ways:

• Visual look of face
• Food intake, drool prevention
• Speech articulation
• Playing musical instruments
• Tactile sensory organ

There are many phrases related to the lips. Here are a few:
Read my lips--meaning "pay close attention to my words" (link)
Lip service--meaning "minimal compliance only" (link)
Hot Lips -- usually a nick name ; Major Margaret J. "Hot Lips" Houlihan (MASH); Oran Thaddeus Page (jazz trumpeter known as Hot Lips Page by the public and Lips Page by his fellow musicians).
Fat Lip--(idiom) A swelling on the lip
Don't give me any lip --meaning "insolent talk" (link)
My lips are sealed --meaning "one will reveal nothing, especially about a secret" (link)

There are many emotions invoked just by looking at someone's lips/mouth. By the look and by the movements. "Thin-lipped" is most often used to describe someone who is strict or stern. In general, fuller and thicker lips are seen as more youthful and more attractive. So I hope I don't ruin the sensual, pleasurable aspect of lip psychology for you by delving into the anatomy of lips. (It hasn't for me.) I want to cover the anatomy prior to moving on to future posts on lip reconstruction and augmentation. The picture above is of Louis Armstrong blowing his trumpet. You can hear him here (A Kiss to Build a Dream On).

ANATOMY
The Upper (Labium superioris) extends from the base of the nose superiorly, to the nasolabial folds laterally, and to the free edge of the vermilion border inferiorly.

The lower lip (Labium inferioris) extends from the superior free vermilion edge superiorly, to the commissures laterally, and to the mandible inferiorly. The lower lip is usually somewhat larger (for youthful lips approximately twice as full as the upper).

The vermilion is the "colored" portion of the lips. The skin here is very thin. In light-skin people, the underlying blood vessels appear more readily through the skin which leads to their notable red coloring. With darker skin color, this effect is less prominent.

Around the circumferential vermilion-skin border, a fine line of pale skin "(the white roll") accentuates the color difference between the vermilion and normal skin. When repairing lacerations, it is crucial to match this "roll". A 1-mm discrepancy can be noticed at a distance of 3 feet.

Cupid's bow is formed by the two "peaks" of vermilion of the upper lip. The philtrum is located between the two raised vertical columns of tissue, from the vermilion to the columella above.

The labiomental (lip-chin)crease passes horizontally in an inverted u-shape across the lower lip, which intraorally corresponds to the depth of the gingivolabial sulcus

BLOOD SUPPLY

The inferior and a superior labial artery are branches of the facial artery. They follow a course beneath the orbicularis oris muscle and anastomose with the contralateral vessel. The superior labial artery usually branches from the facial artery 1.1 cm lateral and 0.9 cm superior to the oral commissure. The inferior labial artery branches from the facial artery 2.6 cm lateral and 1.5 cm inferior to the oral commissure. The facial artery then ascends in the nasolabial groove as the angular artery, forming branches to the nasal ala and anastomosing with the dorsal nasal artery.

LYMPHATIC DRAINAGE

Lymphatic drainage from the upper lip is unilateral except for the midline. The lymphatics coalesce and drain mainly to the ipsilateral submandibular nodes, with some drainage also going to the periparotid lymph nodes. Occasionally, some drainage may be available to the ipsilateral submental lymph nodes.

The lower lip lymphatics also coalesce and drain into bilateral submental nodes from the central lip and unilateral submandibular lymph nodes from the lateral lip.

The submental, submandibular, and parotid lymph nodes are the first level of lymph drainage for the lips. Submental nodes secondarily drain to ipsilateral submandibular nodes, and both submandibular and parotid nodes secondarily drain to ipsilateral jugulodigastric lymph nodes.

SENSORY INNERVATION
The upper lip is innervated by the terminal branch of the maxillary nerve. It supplies sensation to the lateral nasal sidewall, ala, columella, medial cheek, and upper lip.

The lower lip and chin receive sensory innervation from branches of the mandibular nerve. The mental nerve supplies sensation to the lower lip skin down to the labiomental fold and, occasionally, down the chin as well. The nerve is located in the submucosa as it exits the foramen and frequently is visible in this location. The inferior alveolar nerve, a branch of the mandibular nerve, inconsistently supplies the chin and region immediately lateral to it.

MOTOR (MUSCLE) INNERVATION

The motor innervation to the perioral musculature uniformly is from the seventh cranial nerve (CN VII). It is the buccal and marginal branches of the facial nerve that primarily supply innervation to the perioral musculature.

MUSCLES
The perioral musculature (link shows muscles and discusses phonetics) can be classified into 3 groups based on insertion.

• Group I -- insert into the modiolus (a tendinous thickening at each commissure that serves as an attachment site for several of the upper and lower lip muscles)
• Orbicularis oris --forms a sphincter around the mouth. This muscle purses the lips and presses them against the teeth upon contraction.
• Buccinator --functions to press the lips and cheek against the teeth
• Levator anguli oris -- acts to superiorly elevate the commissure
• Depressor anguli oris -- functions to depress and laterally move the commissure
• Zygomaticus major -- elevates and laterally moves the commissure
• Risorius -- draws the commissure laterally and produces the sardonic smile (Warren Oates, 1928-1982)

• Group II -- insert into the upper lip
  • Levator labii superioris -- elevates the upper lip
  • Levator labii superioris alaeque nasi -- dilates the nostril and elevates the upper lip
  • Zygomaticus minor -- elevates and pulls the commissure laterally. Its contraction contributes to the nasolabial fold.
• Group III -- insert into the lower lip
• Depressor labii inferioris -- depress the lower lip and pulls it slightly laterally (outward)
• Mentalis is a paired central muscle of the lower lip. Since its muscle fibers pass in an inferior direction, the action of the mentalis upon contraction is to elevate the lower lip. The insertion site of the mentalis fibers into the dermis can be observed in the pout expression.
• Platysma is a lip depressor.

The picture below is from the second reference article. If you begin with the upper muscle beside the nose as A, then they are as follows: A – m. levator labii superioris, B – m. zygomaticus minor, C - m. zygomaticus major, D - m. risorius, E - m. depressor anguli oris, F - m. labii inferioris, G - m. orbicularis oris

The picture shows the muscles which are important for movement of lips with the vectors of muscle action. The article begins a discussion of relating the 1) implementation of the function of facial muscles and 2) the interconnection with the voice synthesis application in the world of Animation. Isn't it disconcerting to have the sound and picture of a television show not synchronized? It is for me. I have to just listen and not watch when that happens.

It is important to all the functions of the lips/mouth that these muscle work well. I know this first hand from my episode of Bell's Palsy. With poor control over the right side of my mouth, some words were not easy to pronounce (plosive constant's need a good lip seal). You may know it somewhat from the lingering (temporary) effects of local numbing at the dentist office and the lack of drool control.

REFERENCES
Lips and Perioral Region Anatomy; Babak Jahn-Oarwar MD, Keith Blackwell MD; eMedicine Article, October 9, 2007
Visualization of Talking Human Head; Martin Simunek; Department of Computer Science and Engineering, Czech Technical University, Prague / Czech Republic