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Risorius

Facial muscle

Field	Value
Name	Risorius
Latin	musculus risorius
Image	Sobo 1909 260 - Risorius.png
Caption	Superficial muscles of the head and neck, showing the risorius in red. This version of the muscle does not match that shown in most sources.
Image2	Musculusrisorius.png
Caption2	Muscles of the head, face, and neck. Risorius shown in red. This is the most standard version of the direction and origin of the muscle.
Origin	Parotid fascia
Insertion	Modiolus
Blood	Facial artery
Nerve	Buccal branch of the facial nerve
Action	Draws back angle of mouth

The risorius muscle is a highly variable muscle of facial expression. It has numerous and very variable origins, and inserts into the angle of the mouth. It receives motor innervation from branches of facial nerve (CN VII). It may be absent or asymmetrical in some people. It pulls the angle of the mouth sidewise, such as during smiling.

Structure

The risorius muscle is highly variable.

Attachments

Its peripheral attachments may include (some or all of): the parotid fascia, masseteric fascia, the fascia enveloping the pars modiolaris of the platysma muscle, fascia overlying the mastoid part of temporal bone, and/or the zygomatic arch.

Its apical and subapical (i.e. convergent) attachment is at the modiolus.

Innervation

The risorius receives motor innervation from the buccal branch of the facial nerve (CN VII).

Vasculature

The risorius receives arterial supply mostly from the superior labial artery.

Variation

The risorius muscle is highly variable. It ranges in form from one or more slender bundles to a wide (yet thin) fan. It may be absent in a significant minority of people, and may be asymmetrical.

Relations

It is superficial to the masseter muscle, partially overlying it.

Function

The risorius muscle draws the angle of the mouth lateral-ward. It participates in producing facial expressions like a smile, grin, or laugh.

Clinical significance

Because it partially overlies the masseter muscle, it may be unintentionally affected during botox injections, resulting in unnatural facial expressions.

Other animals

It has been suggested that the risorius muscle is only found in Homininae (African great apes and humans).

Etymology

From the Latin rīsor (“laugher, mocker”) + -ius (adjectival suffix), literally, "the laughing muscle".

Additional images

File:Risorius animation small.gif|Position of risorius.

References

Standring, Susan. (2020). "Gray's Anatomy: The Anatomical Basis of Clinical Practice".
(2008). "Selection for universal facial emotion". Emotion.
(December 2014). "The Risorius Muscle: Anatomic Considerations With Reference to Botulinum Neurotoxin Injection for Masseteric Hypertrophy". Dermatologic Surgery.
Wilson, P. D.. (2014). "Reference Module in Biomedical Sciences". [[Elsevier]].
(2011). "Soft-tissue anatomy of the primates: Phylogenetic analyses based on the muscles of the head, neck, pectoral region and upper limb, with notes on the evolution of these muscles". Journal of Anatomy.

Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

muscles-of-the-head-and-neck

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