The Muscles of Facial Expression

Introduction to Muscles of Facial Expression

In this section, Dr. Connor Boylan introduces the topic of muscles of facial expression and explains how they are innervated by the facial nerve.

Facial Nerve

• The facial nerve is the seventh cranial nerve that supplies the muscles of facial expression.

• It arises from the ventrolateral ponto medullary junction of the brain stem and passes through various structures before exiting through the stylomastoid foramen.

• The facial nerve has six terminal branches that supply different regions of the face, including posterior auricular, temporal, zygomatic, buccal, marginal mandibular, and cervical nerves.

Muscles of Facial Expression

• The muscles of facial expression move small or large parts of the face to express emotions and perform specific actions like speaking or chewing.

• Most muscles originate from bones in the viscero cranium and insert directly into overlying skin.

• Only a few muscles are innervated by one nerve only; most have dual supply from two adjacent nerves.

Posterior Auricular Nerve

In this section, Dr. Boylan discusses the posterior auricular nerve and its three associated muscles.

Auricularis Muscles

• The three muscles associated with the posterior auricular nerve are auricularis posterior (pulls ear backwards), auricularis superior (pulls ear upwards), and auricularis anterior (pulls ear forwards).

Temporal Nerve

In this section, Dr. Boylan discusses the temporal nerve and its associated muscles.

Temporal Branch

• The temporal branch of the facial nerve splits into two more branches that supply the frontalis muscle (raises eyebrows) and orbicularis oculi muscle (closes eyelids).

Zygomatic Nerve

In this section, Dr. Boylan discusses the zygomatic nerve and its associated muscles.

Zygomatic Branch

• The zygomatic branch of the facial nerve supplies the zygomaticus major (raises corner of mouth), zygomaticus minor (raises upper lip), and levator labii superioris (raises upper lip).

Buccal Nerve

In this section, Dr. Boylan discusses the buccal nerve and its associated muscles.

Buccal Branch

• The buccal branch of the facial nerve supplies the buccinator muscle (compresses cheek), orbicularis oris muscle (closes lips), and risorius muscle (retracts corner of mouth).

Marginal Mandibular Nerve

In this section, Dr. Boylan discusses the marginal mandibular nerve and its associated muscles.

Marginal Mandibular Branch

• The marginal mandibular branch of the facial nerve supplies the depressor anguli oris muscle (pulls corners of mouth downwards), depressor labii inferioris muscle (pulls lower lip downwards), mentalis muscle (protrudes lower lip), and platysma muscle (depresses mandible).

Cervical Nerve

In this section, Dr. Boylan discusses the cervical nerve and its associated muscles.

Cervical Branch

• The cervical branch of the facial nerve supplies the platysma muscle (depresses mandible).

Muscles of Facial Expression

This video discusses the muscles of facial expression, their innervation, and functions.

Frontalis Muscle

• The frontalis muscle is located in the forehead.

• It raises the eyebrows and tensions the scalp.

• Innervated entirely by the temporal nerve.

Corrugator Supercilia Muscles

• These small thin muscles sit under the eyebrows on both sides.

• They draw the eyebrows inferior medially.

• Innervated purely by the temporal nerve.

Depressor Supercilii Muscles

• These two triangular shaped muscles pull the eyebrows downwards.

• Innervated solely by the temporal nerve.

Procerus Muscle

• The procerus muscle goes from fascia over nasal bone to skin of forehead and pulls medial eyebrow downwards.

• Receives innervation from both temporal and zygomatic nerves.

Orbicularis Oculi Muscle

• The orbicularis oculi muscle surrounds the eye.

• It can be divided into a palpable part which forms inner ring and an orbital part which forms outer ring.

• Palpable part periodically involuntarily contracts to aid blinking reflex whilst orbital part can contract to more forcefully close eye when whole orbicularis oculi contracts together it holds eye tightly closed.

Levator Nasolabialis Muscle

• This has a medial and lateral part that connects to ayla cartilage of nose and upper lip respectively.

• Pulls corners of nose and upper lip superiorly.

• Innervated by zygomatic and buccal nerves together.

Depressor Septem Muscles

• These tiny muscles attach to septum and ailer of nose to pull them downwards.

• Innervated by zygomatic and buccal nerves together.

Levator Labi Superioris Muscle

• Acts in a similar way to the levator nasolabialis to lift the upper lip.

• Innervated by zygomatic and buccal nerves together.

Levator Anguli Oris Muscle

• Attaches to the corner of the mouth to lift it upwards.

• Innervated by zygomatic and buccal nerves together.

Zygomaticus Major and Minor Muscles

• These muscles originate from the zygomatic bone of the facial skeleton.

• They act with levator anguli oris to lift the upper lip and corners of the mouth superiorly as well as a little bit laterally.

• Innervated by zygomatic and buccal nerves together.

Nasalis Muscle

• This muscle acts solely on the nares or nostrils.

• Can be divided into a transverse part which constricts nostrils and an ayla part which dilates them.

• Innervated by buccal nerve only.

Buccinator Muscle

• Sits deep inside cheek and attaches to corners of mouth.

• Acts mostly to compress cheeks and thus helps move food around mouth when chewing.

• Innervated by buccal nerve only.

Risorius Muscle

• Pulls side of mouth laterally protruding lips and pushing them together for example when laughing

• Innervated by marginal mandibular branch of facial nerve.

Anatomy of Facial Muscles

This video covers the anatomy of facial muscles, their actions, and the nerves that innervate them.

Muscles of Facial Expression

• The muscles of facial expression are responsible for producing a wide range of facial expressions.

• There are five main groups of muscles: the epicranius muscle, orbicularis oculi muscle, zygomaticus muscle, buccinator muscle, and platysma muscle.

• Each group is innervated by a different nerve or set of nerves.

• The depressor anguli oris muscle pulls the corners of the mouth downwards into a frown. It shares an innervation with levator anguli oris.

• Depressor labii inferioris inserts into the middle portion of the lower lip and acts to pull it downwards.

• Mentalis muscle originates from the mandible and inserts directly into the skin overlying the chin or mental region. It protrudes the lower lip and produces dimpling effect seen in some people when they're very sad or crying.

• Platysma originates all the way down in the chest from pectoral fascia and deltoid fascia overlying pectoralis major and deltoid muscles. Its action is to tense skin on neck as well as depress mandible slightly.

Conclusion

This video provides a comprehensive overview of every single muscle involved in facial expression along with their actions and innervations.