16.muscles Of The Mimic.docx

Muscles of the mimic  The muscles of facial expression are located in the subcutaneous tissue, originating from bone / fascia, and inserting onto the skin.  By contracting, the muscles pull on the skin and exert their effects.  They are the only group of muscles that insert into skin.  These muscles have a common embryonic origin – the 2nd pharyngeal arch.  They migrate from the arch, taking their nerve supply with them.  As such, all the muscles of facial expression are innervated by the facial nerve.  The facial muscles can broadly be split into the following groups: forehead & epicranium, orbital, nasal, oral, others, auricular. Forehead and Epicranium

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Occipitofrontal muscle

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Venter frontalis (frontal muscle)

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Venter occipitalis (occipital muscle)

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Temporoparietal muscle

Orbital group 

The orbital group of facial muscles contains 3 muscles: Orbicularis oculi muscle; Corrugator supercilii muscle; Depressor supercilii muscle

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These muscles control the movements of the eyelids, important in protecting the cornea from damage.

Fig 1.0 - Posterior view of the orbital muscles of facial expression

Orbicularis Oculi  This muscle surrounds the eye socket and extends into the eyelid. It can be functionally split into two parts; the outer orbital part and inner palpebral part. Origin: Insertion: Innervation: Facial nerve Vascularization: Actions: The palpebral part of the muscle performs gentle closure of the eyelid, whereas the orbital portion closes more forcefully. Relations: Corrugator Supercilii

The corrugator supercilii is a much smaller muscle, and is located posteriorly to the orbicularis oculi muscle.

Attachments: It originates from the superciliary arch, running in a superolateral direction. It inserts into the skin of the eyebrow. Actions: It acts to draw the eyebrows together, creating vertical wrinkles on the bridge of the nose. Innervation: Facial nerve. Depressor supercilii The depressor supercilii muscle is a small, two-headed muscle in the region of the palpebral fissure. It counts among the mimic muscles.

Note: Some authors consider the depressor supercilii musce not an independent muscle, but they attribute it to the orbicularis oculi muscle, or to the corrugator supercilii muscle. 2 Devolution The depressor supercilii muscle has its origin at the frontal process of the maxilla and at the superciliary arch of the frontal bone. Based on recent findings, the muscle has two heads, and the artery and angular vein pass between them. Its fibers go straight into cranial direction. There, they insert into the skin of the medial eyebrow. 3 Innervation The depressor supercilii muscle is innervated by the temporal branches of the VIIth cranial nerve (facial nerve). 4 Function The depressor supercilii muscle draws the eyebrow downwards. The muscle has grown together with the corium, which causes the skin to follow the muscle movements. Thereby, together with the procerus musle, it creates a horizontal wrinkle in the glabellar region, the so-called glabellar frown line.

Nose

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Nasal muscle

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Depressor septi muscle

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Procerus muscle

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Levator labii superioris alaeque nasi muscle 3.4 Mouth

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Superficial layer

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Orbicularis ori muscle

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Depressor anguli oris muscle

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Risorius muscle

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Mentalis muscle

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Levator labii superioris muscle

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Greater zygomatic muscle

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Lesser zygomatic muscle

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Deep layer

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Buccinator muscle

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Levator labii inferioris muscle

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Levator anguli oris muscle The levator labii superioris alaeque nasi muscle and the lesser zygomatic muscle are also attributed to the levator labii superioris muscle in anatomic literature, and there, they are called the Caput angulare, respectively Caput zygomaticum, of this muscle. 3.5 Others

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Platysma 3.6 Muscles of the ear In a broader sense, you can also count the muscles of the ear among the mimic muscles. They comprise:

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Anterior auricular muscle

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Posterior auricular muscle

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Superior auricular muscle

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Helicis minor muscle

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Helicis major muscle

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Tragicus muscle

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Antitragicus muscle

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Transversus auricularis muscle

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Obliquus auricularis muscle

4 Innervation The innervation of the mimic muscles is provided by branches of the facial nerve (nerve VII).

5 Function On the one hand, the mimic muscles enable important physiological functions such as the eyelid closure. On the other hand, it forms the base of human mimics and thereby the most important instrument of non-verbal communication.

6 Clinical presentation The function of the mimic muscles is alternated in a characteristic way in different diseases, such as a facial nerve paralysis, where the affected half of the face has a flappy palsy. Tetanus manifests itslef in mimics as Risus sardonicus.

Clinical Relevance: Paralysis to the Orbital Muscles By TeachMeSeries Ltd (2018)Fig 1.2 - Drooping of the lower eyelid, ectropion. Fig 1.1 – Drooping of the lower eyelid, ectropion. If the facial nerve becomes damaged, the orbital muscles will cease to function. As they are the only muscles that can close the eyelids, this has some serious clinical consequences.

The eye cannot shut – this can cause the cornea to dry out. This is known as exposure keratitis. The lower eyelid droops, called ectropion. Lacrimal fluid pools in the lower eyelid, and cannot be spread across the surface of the eye. This can result in a failure to remove debris, and ulceration of the corneal surface. The test for facial nerve palsy involves raising the eyebrows and closing the eyelids