RISORIA MUSCLE: FUNCTIONS, INSERTIONS, RELATIONSHIPS - ANATOMY AND PHYSIOLOGY - 2025

The risorio muscle is considered a muscle of facial expression or mimicry, and it is responsible for manifesting (not producing) the smile on the face. It is a small, bilateral muscle, triangular in shape and made up of several bundles of muscle fibers. It is part of the group of muscles called muscles of facial expression.

They have three important characteristics; The first is that everyone has at least one insertion in the dermis or skin. This is the main characteristic and that also gives them the name of cutaneous muscles.

The insertion at the skin level must exist in order to perform its function of showing different gestures on the face. The second characteristic is that, based on their location, all the muscles of facial expression are arranged around facial cavities. This characteristic classifies the risorio muscle as a periorificial muscle of the mouth.

The third characteristic is that, as its name indicates, these are facial muscles and all are motorly innervated by branches of the facial nerve (CN VII) and supplied by branches of the facial artery.

Function

The main function of the risorio muscle is to retract the labial commissures on both sides, bringing them up and out, increasing the transverse diameter of the mouth (dilating the buccal orifice laterally).

Within the classification according to the location in the periorificial muscles of the mouth, there are two groups that are classified according to their function: the constrictor muscles and the levator muscles.

The constrictor muscles are responsible for pressing or squeezing the oral orifice and are represented by the orbicularis oculi muscle.

For their part, the levator muscles are responsible for raising or dilating the mouth opening. They have inserts that allow superior mobility of the upper lip, lateral mobility through the labial commissures, and lower mobility for the lower lip.

So, according to this classification, the risorio muscle is found within the group of muscles with lateral mobility functions.

Origin and insertion of the risorio muscle

The muscle can originate from one or more bundles that insert into the cellular tissue or the fascia of the parotid region.

Rather, some of these bundles may originate from the sternocleidomastoid muscle and the masseter muscle, and even from the skin over the masseter muscle.

Its bundles of fibers of various origins are directed medially and superficially to insert into the dermis and the mucosa of the labial commissure.

However, there are few details about the exact origin and limits of the risorio muscle in the medical literature. In specialties such as plastic surgery, where surgical interventions for face lifting are performed, the need to know the precise anatomical origin of the muscle is imperative.

For this reason, in 2014 the Aesthetic Surgery Journal published a study carried out at the University of Chulalongkorn, in Korea, on 46 cadaveric specimens, performing dissection of the left perioral cavities to discern the origin of the risorio with respect to the superficial musculoaponeurotic system.

The results obtained showed that 58.7% of the studied laughing muscles had their origin only in the superficial fascial layer of the musculoaponeurotic system.

34.8% had their origin in both the superficial and deep fascial layers of the superficial musculoaponeurotic system, and in 6.5% the fibers originated only from the tendon of the masseter muscle.

Relations

Superficial face

It is intimately related to the dermis in its entirety

Deep face

It is related to the body of the parotid gland, the masseter muscle -which it covers mostly- and the bucinator muscle.

Top edge

It has an almost completely horizontal direction. It is related to the zygomaticus major muscle, from which it is separated by a small triangular space.

Bottom edge

Obliquely ascending it corresponds to the platysma, which closely follows the same direction and with which it is often a bit confused.

Vascularization

The common carotid artery divides to form the internal carotid artery and the external carotid artery.

The external carotid artery has 8 branches. One of these branches is the facial artery, which is directly responsible for the vascularization of the risorio muscle.

Innervation

The risorio muscle receives both sensory and motor nerve information from the facial nerve through its maxillary branch, which also innervates the buccinator and orbicularis muscles of the lips.

References

1. Illustrated Anatomy of the Head and Neck - E-Book. Muscular System. Chapter 4. P 101. Recovered from: books.google.pt
2. Lais Garcia Capel Wenceslau et al. Peripheral facial palsy: muscle activity in different onset times. (2005) Recovered from: scielo.br
3. Jung-Hee Bae, et al. Aesthetic Surgery Journal 2014, Vol. 34 (7) NP43 – NP49 © 2014 The American Society for Aesthetic Plastic Surgery, Inc. Surgical Consideration of the Anatomic Origin of the Risorius in Relation to Facial Planes. Recovered from: watermark.silverchair.com
4. Mimic muscles. Risor and triangular muscle. November 1, 2016. Recovered from: musculosdelamimica.blogspot.pt
5. Facial Weakness. (2016). com. Recovered from: pediatricneuro.com